Temporal changes in gene expression following cryogenic rat brain injury

Role and Importance of IGF-1 in Traumatic Brain Injuries

It is increasingly affirmed that most of the long-term consequences of TBI are due to molecular and cellular changes occurring during the acute phase of the injury and which may, afterwards, persist or progress. Understanding how to prevent secondary damage and improve outcome in trauma patients, has been always a target of scientific interest. Plans of studies focused their attention on the posttraumatic neuroendocrine dysfunction in order to achieve a correlation between hormone blood level and TBI outcomes. The somatotropic axis (GH and IGF-1) seems to be the most affected, with different alterations between the acute and late phases. IGF-1 plays an important role in brain growth and development, and it is related to repair responses to damage for both the central and peripheral nervous system. The IGF-1 blood levels result prone to decrease during both the early and late phases after TBI. Despite this, experimental studies on animals have shown that the CNS responds to the injury upregulating the expression of IGF-1; thus it appears to be related to the secondary mechanisms of response to posttraumatic damage. We review the mechanisms involving IGF-1 in TBI, analyzing how its expression and metabolism may affect prognosis and outcome in head trauma patients.

Endogenous repair signaling after brain injury and complementary bioengineering approaches to enhance neural regeneration

Traumatic brain injury (TBI) affects 5.3 million Americans annually. Despite the many long-term deficits associated with TBI, there currently are no clinically available therapies that directly address the underlying pathologies contributing to these deficits. Preclinical studies have investigated various therapeutic approaches for TBI: two such approaches are stem cell transplantation and delivery of bioactive factors to mitigate the biochemical insult affiliated with TBI. However, success with either of these approaches has been limited largely due to the complexity of the injury microenvironment. As such, this review outlines the many factors of the injury microenvironment that mediate endogenous neural regeneration after TBI and the corresponding bioengineering approaches that harness these inherent signaling mechanisms to further amplify regenerative efforts.

Blood-brain barrier pathophysiology in traumatic brain injury

The blood-brain barrier (BBB) is formed by tightly connected cerebrovascular endothelial cells, but its normal function also depends on paracrine interactions between the brain endothelium and closely located glia. There is a growing consensus that brain injury, whether it is ischemic, hemorrhagic, or traumatic, leads to dysfunction of the BBB. Changes in BBB function observed after injury are thought to contribute to the loss of neural tissue and to affect the response to neuroprotective drugs. New discoveries suggest that considering the entire gliovascular unit, rather than the BBB alone, will expand our understanding of the cellular and molecular responses to traumatic brain injury (TBI). This review will address the BBB breakdown in TBI, the role of blood-borne factors in affecting the function of the gliovascular unit, changes in BBB permeability and post-traumatic edema formation, and the major pathophysiological factors associated with TBI that may contribute to post-traumatic dysfunction of the BBB. The key role of neuroinflammation and the possible effect of injury on transport mechanisms at the BBB will also be described. Finally, the potential role of the BBB as a target for therapeutic intervention through restoration of normal BBB function after injury and/or by harnessing the cerebrovascular endothelium to produce neurotrophic growth factors will be discussed.

Simulated microgravity maintains the undifferentiated state and enhances the neural repair potential of bone marrow stromal cells

Recently, regenerative medicine with bone marrow stromal cells (BMSCs) has gained significant attention for the treatment of central nervous system diseases. Here, we investigated the activity of BMSCs under simulated microgravity conditions. Mouse BMSCs (mBMSCs) were isolated from C57BL/6 mice and harvested in 1G condition. Subjects were divided into 4 groups: cultured under simulated microgravity and 1G condition in growth medium and neural differentiation medium. After 7 days of culture, the mBMSCs were used for morphological analysis, reverse transcription (RT)-polymerase chain reaction, immunostaining analysis, and grafting. Neural-induced mBMSCs cultured under 1G conditions exhibited neural differentiation, whereas those cultured under simulated microgravity did not. Moreover, under simulated microgravity conditions, mBMSCs could be cultured in an undifferentiated state. Next, we intravenously injected cells into a mouse model of cerebral contusion. Graft mBMSCs cultured under simulated microgravity exhibited greater survival in the damaged region, and the motor function of the grafted mice improved significantly. mBMSCs cultured under simulated microgravity expressed CXCR4 on their cell membrane. Our study indicates that culturing cells under simulated microgravity enhances their survival rate by maintaining an undifferentiated state of cells, making this a potentially attractive method for culturing donor cells to be used in grafting.

Type IV collagen induces expression of thrombospondin-1 that is mediated by integrin alpha1beta1 in astrocytes

Following brain injury, thrombospondin-1 (TSP-1) is involved in angiogenesis and synaptic recovery. In this study, we used a cold injury-model and found that TSP-1 mRNA was markedly upregulated after brain injury. Immunohistochemistry showed that TSP-1 was upregulated in both the core of the lesion and in the perilesional area of injured brain tissue. Numerous astrocytes immunopositive for glial fibrillary acidic protein (GFAP) were found in the perilesional area, and TSP-1 was also expressed in almost all astrocytes surrounding blood vessels at 4 days after injury. Next, we examined the influence of vascular basement membrane components on TSP-1 expression. When astrocytes were cultured on type IV collagen, TSP-1 was significantly upregulated compared with the expression when cells were grown on laminin, fibronectin, or poly-L-lysine. This increase occurred exclusively when astrocytes were grown on the native form of type IV collagen but not on the heat-denatured form or the non-collagenous 1 domain. Further, integrin alpha1 and beta1 mRNAs were upregulated concomitantly with GFAP mRNA, and integrin alpha1 protein was localized to the endfeet of astrocytes that surrounded blood vessels in the injured brain. Using function-blocking antibodies, we found that the effect of type IV collagen was attributed to integrin alpha1beta1 in primary astrocytes. Collectively, our results suggest that vascular basement membrane components substantially impact gene expression in astrocytes during brain tissue repair.

Tendon healing in vivo: gene expression and production of multiple growth factors in early tendon healing period

PURPOSE

The actions of growth factors during healing of injured flexor tendons are not well characterized, although information pertinent to some individual growth factors is available. We studied gene expression and protein production of a number of growth factors at several time points during the early healing period in a chicken model.

METHODS

Seventy-four long toes of 37 white Leghorn chickens were used. The flexor digitorum profundus tendons of 60 toes were surgically repaired after complete transection and were harvested for analysis 3, 5, 7, 9, 14, and 21 days after surgery. The expression of 6 growth factors was studied at 4 time points after surgery with real-time quantitative polymerase chain reactions, and production and distribution of 3 growth factors at all 6 time points were studied by immunohistochemical staining with antibodies. Fourteen tendons that had no surgery served as day 0 controls. Tendon healing status was also assessed histologically.

RESULTS

Throughout the early tendon healing period, connective tissue growth factor (CTGF) and transforming growth factor beta (TGF-beta) showed high levels of gene expression. Levels of gene expression of vascular endothelial growth factor (VEGF) and insulin-like growth factor 1 (IGF-1) were high or moderately high. Expression of the TGF-beta gene was upregulated after injury, whereas the basic fibroblast growth factor (bFGF) gene was downregulated at all postsurgical time points and expressed at the lowest levels among 6 growth factor genes 2 to 3 weeks after surgery. The platelet-derived growth factor B (PDGF-B) gene was also minimally expressed. Findings of immunohistochemistry corresponded to TGF-beta, bFGF, and IGF-1 gene expression.

CONCLUSIONS

In this model, up to 3 weeks after surgery, gene expression and production of TGF-beta are high and are upregulated in this healing period. However, expression of the bFGF gene and protein is low and decreases in the healing tendon. The CTGF, VEGF, and IGF-1 genes are expressed at high or moderately high levels, but PDGF-B is minimally expressed.

Diverging mechanisms for TNF-alpha receptors in normal mouse brains and in functional recovery after injury: From gene to behavior

Cytokines, such as tumour necrosis factor (TNF)-alpha and lymphotoxin-alpha, have been described widely to play important roles in the brain in physiologic conditions and after traumatic injury. However, the exact mechanisms involved in their function have not been fully elucidated. We give some insight on their role by using animals lacking either Type 1 receptor (TNFR1KO) or Type 2 (TNFR2KO) and their controls (C57Bl/6). Both TNFR1KO and to a greater extent TNFR2KO mice showed increased exploration/activity neurobehavioral traits in the hole board test, such as rearings, head dippings, and ambulations, compared with wild-type mice, suggesting an inhibitory role of TNFR1/TNFR2 signaling. In contrast, no significant differences were observed in the elevated plus maze test, ruling out a major role of these receptors in the control of anxiety. We next evaluated the response to a freeze injury to the somatosensorial cortex. The effect of the cryolesion on motor function was evaluated with the horizontal ladder beam test, and the results showed that both TNFR1KO and TNFR2KO mice made fewer errors, suggesting a detrimental role for TNFR1/TNFR2 signaling for coping with brain damage. Expression of approximately 22600 genes was analyzed using an Affymetrix chip (MOE430A) at 0 (unlesioned), 1, or 4 days post-lesion in the three strains. The results show a unique and major role of both TNF receptors on the pattern of gene expression elicited by the injury but also in normal conditions, and suggest that blocking of TNFR1/TNFR2 receptors may be beneficial after a traumatic brain injury.

Somatostatin in the dentate gyrus

The neuropeptide somatostatin (SST) is expressed in a discrete population of interneurons in the dentate gyrus. These interneurons have their soma in the hilus and project to the outer molecular layer onto dendrites of dentate granule cells, adjacent to perforant path input. SST-containing interneurons are very sensitive to excitotoxicty, and thus are vulnerable to a variety of neurological diseases and insults, including epilepsy, Alzheimer's disease, traumatic brain injury, and ischemia. The SST gene contains a prototypical cyclic AMP response element (CRE) site. Such a regulatory site confers activity-dependence to the gene, such that it is turned on when neuronal activity is high. Thus SST expression is increased by pathological conditions such as seizures and by natural stimulation such as environmental enrichment. SST may play an important role in cognition by modulating the response of neurons to synaptic input. In the dentate, SST and the related peptide cortistatin (CST) reduce the likelihood of generating long-term potentiation, a cellular process involved in learning and memory. Thus these neuropeptides would increase the threshold of input required for acquisition of new memories, increasing "signal to noise" to filter out irrelevant environmental cues. The major mechanism through which SST inhibits LTP is likely through inhibition of voltage-gated Ca(2+) channels on dentate granule cell dendrites. Transgenic overexpression of CST in the dentate leads to profound deficits in spatial learning and memory, validating its role in cognitive processing. A reduction of synaptic potentiation by SST and CST in dentate may also contribute to the well-characterized antiepileptic properties of these neuropeptides. Thus SST and CST are important neuromodulators in the dentate gyrus, and disruption of this signaling system may have major impact on hippocampal function.

Novel roles for metallothionein-I + II (MT-I + II) in defense responses, neurogenesis, and tissue restoration after traumatic brain injury: Insights from global gene expression profiling in wild-type and MT-I + II knockout mice

Traumatic injury to the brain is one of the leading causes of injury-related death or disability, especially among young people. Inflammatory processes and oxidative stress likely underlie much of the damage elicited by injury, but the full repertoire of responses involved is not well known. A genomic approach, such as the use of microarrays, provides much insight in this regard, especially if combined with the use of gene-targeted animals. We report here the results of one of these studies comparing wild-type and metallothionein-I + II knockout mice subjected to a cryolesion of the somatosensorial cortex and killed at 0, 1, 4, 8, and 16 days postlesion (dpl) using Affymetrix genechips/oligonucleotide arrays interrogating approximately 10,000 different murine genes (MG_U74Av2). Hierarchical clustering analysis of these genes readily shows an orderly pattern of gene responses at specific times consistent with the processes involved in the initial tissue injury and later regeneration of the parenchyma, as well as a prominent effect of MT-I + II deficiency. The results thoroughly confirmed the importance of the antioxidant proteins MT-I + II in the response of the brain to injury and opened new avenues that were confirmed by immunohistochemistry. Data in KO, MT-I-overexpressing, and MT-II-injected mice strongly suggest a role of these proteins in postlesional activation of neural stem cells.

Increased growth factor expression and cell proliferation after contusive spinal cord injury

The damage caused by traumatic central nervous system (CNS) injury can be divided into two phases: primary and secondary. The initial injury destroys many of the local neurons and glia and triggers secondary mechanisms that result in further cell loss. Approximately 50% of the astrocytes and oligodendrocytes in the spared white matter of the epicenter die by 24 h after spinal cord injury (SCI), but their densities return to normal levels by 6 weeks. This repopulation is largely due to the proliferation of local progenitors that divide in response of CNS injury. Previous studies indicate that the secondary events that cause cell death after SCI also increase the local levels of several growth factors that stimulate the proliferation of these endogenous progenitors. We compared the spatial pattern of the post-injury up-regulation of the pro-mitotic growth factors with that of 5-bromodeoxyuridine (BrdU) incorporation to determine if each could play a role in proliferation. Three days after a standard contusive SCI or laminectomy, animals received intraperitoneal BrdU injections to label dividing cells and were perfused 2 h after the last injection. Immunohistochemistry for BrdU and basic fibroblast growth factor (FGF2) and in situ hybridization for ciliary neurotrophic factor (CNTF) and glial growth factor (GGF2) mRNA were used to compare the number of dividing cells with growth factor levels in sections 2 and 4 mm from the epicenter. All three growth factors are significantly up-regulated 3 days after SCI, when cell proliferation is maximal. The increase in GGF2 and FGF2 levels is highest in sections 2 mm rostral to the epicenter, mimicking BrdU incorporation. Addition of rhGGF2 to cultured cells isolated from the spinal cord 3 days after SCI increased the number of NG2+ glial progenitors. These data suggest that FGF2 and GGF2 may contribute to the spontaneous recovery observed after SCI by stimulating the proliferation of local progenitors that help repopulate the injured cord.

Future trends in neurovirology: neuronal survival during virus infection and analysis of virus-specific T cells in central nervous system tissues

The recent ability to quantitate and localize the interaction of antigen-specific T cells in the central nervous system during infectious and autoimmune diseases will greatly enhance our understanding of the molecular and biologic basis of virus-induced diseases of the nervous and other systems.

Laser microdissection reveals regional and cellular differences in GFAP mRNA upregulation following brain injury, axonal denervation, and amyloid plaque deposition

Astrocytes are one of the major cell types responding to central nervous system injury. Upregulation of the astrocytic intermediate filament molecule glial fibrillary acidic protein (GFAP) is a key event associated with this reaction. To study the response of astrocytes to different types of brain lesions, GFAP mRNA expression was analyzed by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) in mouse brain following injury, axonal denervation (entorhinal cortex lesion), and amyloid plaque deposition (APP23 transgenic mice). Analysis of tissue areas surrounding a lesion revealed a 21-fold increase of GFAP mRNA in tissue surrounding an injury site, a 6-fold increase in denervated tissue areas, and a 5-fold increase in plaque containing tissue. To this GFAP mRNA increase, astrocytic proliferation and migration as well as an increase of cellular GFAP mRNA expression within astrocytes could have contributed. To determine the degree of GFAP mRNA upregulation in individual astrocytes, an immunofluorescence protocol was developed to harvest astrocytes selectively by laser microdissection and preserve intact RNA. qRT-PCR analysis of GFAP mRNA in microdissected astrocytes revealed an 82-fold increase in astrocytes surrounding an injury site, a 30-fold increase in astrocytes located in a denervation zone, and an 18-fold increase in astrocytes surrounding an amyloid plaque. These data demonstrate that GFAP mRNA is strongly upregulated within individual reactive astrocytes in response to a lesion. Because astrocytic GFAP mRNA upregulation differs among the three lesioning paradigms, we conclude that the lesion type is an important determinant of postlesional astrocytic reactivity.

Transplantation of motoneurons derived from MASH1-transfected mouse ES cells reconstitutes neural networks and improves motor function in hemiplegic mice

Mouse embryonic stem (ES) cells were transfected with a MASH1 expression vector and G418-resistant cells were selected. The MASH1-transfected cells became neuron-like appearance and expressed betaIIItubulin and panNCAM. Glial fibrillary acidic protein (GFAP) and galactocerebroside (GalC)-expressing cells were rarely detected. Half of the neural cells differentiated into the Islet1+ motoneuron lineage. Thus, we obtained motoneuron lineage-enriched neuronal cells by transfection of ES cells with MASH1. A hemiplegic model of mice was developed by cryogenic injury of the motor cortex, and motoneuron lineage-enriched neuronal cells were transplanted underneath the injured motor cortex neighboring the periventricular region. The motor function of the recipients was assessed by a beam walking and rotarod tests, whereby the results gradually improved, but little improvement was observed in vehicle injected control mice. We found that the grafted cells not only remained close to the implantation site, but also exhibited substantial migration, penetrating into the damaged lesion in a directed manner up to the cortical region. Grafted neuronal cells that had migrated into the cortex were elongated axon-positive for neurofilament middle chain (NFM). Synaptophysin immunostaining showed a positive staining pattern around the graft, suggesting that the transplanted neurons interacted with the recipient neurons to form a neural network. Our study suggests that the motoneuron lineage can be induced from ES cells, and grafted cells adapt to the host environment and can reconstitute a neural network to improve motor function of a paralyzed limb.

Anatomical and functional recovery by embryonic stem cell-derived neural tissue of a mouse model of brain damage

We have treated undifferentiated mouse embryonic stem (ES) cells with all-trans retinoic acid (RA) to induce differentiation in vitro into neuron-like cells with good cell viability for use as a graft. Furthermore, we asked whether the RA-induced neuron-like cells restored neurological dysfunction. To this end, the cells were transplanted into right hemiplegia model of mice, developed by a cryogenic injury of motor cortex. Motor function of the recipients was gradually improved, whereas little improvement was observed in control mice. The lesion showed clustering of mature and almost mature neuron-like cells in mice transplanted with the RA-treated cells. The grafted cells had synaptic vesicles. This finding may suggest their maturation and synaptic connection in the recipient brain. Even though further study is necessary to elucidate molecular and cellular mechanisms responsible for the functional recovery, we consider that the ES cells may have advantage for use as a donor source in various neurological disorders including motor dysfunction.

Transplantation of motoneuron-enriched neural cells derived from mouse embryonic stem cells improves motor function of hemiplegic mice

Embryonic stem (ES) cells are expected to be a potential donor source for neural transplantation. We have obtained motoneuron-enriched neural progenitor cells by culturing mouse ES cells with retinoic acid (RA). The cells also expressed mRNA of a neurotrophic factor, neurotrophin-3 (NT-3). The left motor cortex area of mice was damaged by cryogenic brain injury, and the neural cells were transplanted underneath the injured motor cortex, neighboring to the paraventricular region. We found that the cells expressing neuronal phenotypes not only remained close to the implantation site, but also exhibited substantial migration penetrating into the damaged lesion, in a seemingly directed manner up to cortical region. We found that some of the neural cells differentiated into Islet1-positive motoneurons. It seems likely that the ability of the ES cell-derived neural progenitor cells to respond in vivo to guidance cues and signals that can direct their migration and differentiation may contribute to functional recovery of the recipient mice. We found that an "island of the mature neuronal cells" of recipient origin emerged in the damaged motor cortex. This may be associated with the neuroprotective effects of the ES cell-derived neural cells. The ES cells differentiated into CD31+ vasculoendothelial cells with the RA treatment in vitro. Furthermore, the grafted cells may provide sufficient neurotrophic factors such as NT-3 for neuroprotection and regeneration. The grafted neural cells that migrated into residual cortex and differentiated into neurons had purposefully elongated axons that were stained with anti-neurofilament middle chain (NFM) antibody. Our study suggests that motoneurons can be induced from ES cells, and ES cells become virtually an unlimited source of cells for experimental and clinical neural cell transplantation.

Role of metallothionein-III following central nervous system damage

We evaluated the physiological relevance of metallothionein-III (MT-III) in the central nervous system following damage caused by a focal cryolesion onto the cortex by studying Mt3-null mice. In normal mice, dramatic astrogliosis and microgliosis and T-cell infiltration were observed in the area surrounding the lesioned tissue, along with signs of increased oxidative stress and apoptosis. There was also significant upregulation of cytokines/growth factors such as tumor necrosis factor-alpha, interleukin (IL)-1 alpha/beta, and IL-6 as measured by ribonuclease protection assay. Mt3-null mice did not differ from control mice in these responses, in sharp contrast to results obtained in Mt1- Mt2-null mice. In contrast, Mt3-null mice showed increased expression of several neurotrophins as well as of the neuronal sprouting factor GAP-43. Thus, unlike MT-I and MT-II, MT-III does not affect the inflammatory response elicited in the central nervous system by a cryoinjury, nor does it serve an important antioxidant role, but it may influence neuronal regeneration during the recovery process.

Patterns of immunocytochemical staining for ferritin and transferrin in the human spinal cord following traumatic injury

Normally Fe(2+) is strictly controlled within the central nervous system (CNS) because of its potential to react with oxygen and form free radicals.(1,2) Traumatic spinal cord injury (TSCI) leads to cell damage and haemorrhage, both of which may increase the pool of free iron.(3) The aim of this study was to examine the response to TSCI of the iron storage protein ferritin (Ft) and the iron transport protein transferrin (Tf). The study found a significant increase in Ft positive cells compared to controls and a significant correlation between the number of Ft positive cells and the severity of injury. Significantly fewer Tf positive cells were seen in the trauma cases compared to the control and there was no relation with the severity of injury. These observations suggest a disturbance in normal iron metabolism within the spinal cord following injury, with possible implications for free radical mediated secondary damage.

Genes preferentially induced by depolarization after concussive brain injury: effects of age and injury severity

Fluid percussion (FP) brain injury leads to immediate indiscriminate depolarization and massive potassium efflux from neurons. Using Northern blotting, we examined the post-FP expression of primary response/immediate early genes previously described as induced by depolarization in brain. RNA from ipsilateral and contralateral hippocampus was harvested from immature and adult rats 1 h following mild, moderate, or severe lateral fluid percussion injury and compared against age-matched sham animals. C-fos gene expression was used as a positive control and showed marked induction in both pups (6-25-fold with increasing severity) and adults (9.7-17.1-fold). Kinase-induced-by-depolarization-1 (KID-1) and salt-inducible kinase (SIK) gene expression was increased in adult (KID-1 1.5-1.6-fold; SIK 1.3-3.9-fold) but not developing rats. NGFI-b RNA was elevated after injury in both ages (pups 1.8-6.1-fold; adults 3.5-5-fold), in a pattern similar to that seen for c-fos. Secretogranin I (sec I) demonstrated no significant changes. Synaptotagmin IV (syt IV) was induced only following severe injury in the immature rats (1.4-fold). Our results reveal specific severity- and age-dependent patterns of hippocampal immediate early gene expression for these depolarization-induced genes following traumatic brain injury. Differential expression of these genes may be an important determinant of the distinct molecular responses of the brain to varying severities of trauma experienced at different ages.

Interleukin-6 promotes post-traumatic healing in the central nervous system

The central nervous system (CNS) is an immune-privileged site where the role of immune cells and mediators in traumatic brain injury is poorly understood. Previously we have demonstrated that interleukin (IL)-6, a cytokine that acts on a wide range of tissues influencing cell growth and differentiation, is an agonist for vascular endothelial growth factor (VEGF), in in vitro vascularization assays for brain microvessel endothelial cells. In this present work we focus on the role of IL-6 in promoting tissue repair in the CNS in vivo. An aseptic cerebral injury (ACI) was created in the right parietal cortex, using both wild type (C57Bl/6J) and IL-6-deficient (C57Bl/6J-IL-6-/-) mice to study the consequences of the absence of IL-6 on the pathology of brain injuries. We monitored the immediate, early, and late responses to this traumatic injury by characterizing several histologic features in the CNS at days 1, 4, 7 and 14 following injury. Acellular necrosis, cellular infiltration, and re-vascularization were characterized in the injured tissues, and each of these histologic features was individually graded and totaled to assign a healing index. IL-6-deficient mice were found to have a comparatively slower rate of recovery and healing. Furthermore, fluorescein isothiocyanate (FITC)-dextran intravenous injection demonstrated leaky vessels in IL-6-deficient but not in wild type animals following ACI. Additionally, chronic expression of IL-6 in the CNS using transgenic GFAP-IL-6 mice resulted in more rapid healing following ACI. The accelerated tissue repair in GFAP-IL-6 transgenic animals is primarily due to extensive re-vascularization as detected by endothelial cell markers. Combined, this data suggests an important role of IL-6 in tissue repair processes following traumatic injury in the CNS.

Increase in wound breaking strength in rats in the presence of positively charged dextran beads correlates with an increase in endogenous transforming growth factor-beta1 and its receptor TGF-betaRI in close proximity to the wound

We have previously shown that positively charged beads (DEAE A25) increase wound breaking strength in linear incisions in rats and nonhuman primates at days 10-14 post-wounding. The increased wound strength may result in part from a stimulation of cells adjacent to the DEAE A25 beads to produce growth factors important for wound healing. In this report, we investigate this hypothesis by comparing the relative expression levels of transforming growth factor-beta1 and its receptor transforming growth factor-beta receptor type I in DEAE A25-treated and contralateral untreated rat linear incisions. DEAE A25-treated incisions were stronger than untreated control wounds at 3 days post-wounding, and the difference in breaking strength reached statistical significance at days 5, 7 and 10. Immunohistochemical analysis revealed a significant increase in transforming growth factor-beta1 and transforming growth factor-beta receptor type I expression in DEAE A25-treated incisions, up to 7 days post-wounding, as compared to untreated control wounds. FACS analysis revealed that macrophage cell lines exposed to DEAE A25 in vitro upregulate transforming growth factor-beta1 and transforming growth factor-beta receptor type I expression by 2-3 fold. Therefore, the increase in expression of transforming growth factor-beta1 and transforming growth factor-beta receptor type I in DEAE A25-treated incisions may be due to an increase in the concentration of macrophages adjacent to DEAE A25 beads, as well as the stimulation of individual macrophages to produce greater amounts of transforming growth factor-beta1 and transforming growth factor-beta receptor type I. This study also supports the significance of transforming growth factor-beta1 in wound healing.

The megencephaly mouse has disturbances in the insulin-like growth factor (IGF) system

Megencephaly, enlarged brain, is a major sign in several human neurological diseases. The mouse model for megencephaly, mceph/mceph, has an enlarged brain and a lowered body weight. In addition, it displays several neurological and motoric disturbances. Previous studies suggest that the brain enlargement results from hypertrophy of the brain cells, rather than hyperplasia. No structural abnormalities, edema or increased myelination have been found. In this study, a major imbalance in the mRNA expression of molecules in the insulin-like growth factor (IGF) system was found in brains of 9-10 weeks old mceph/mceph mice compared to +/+ wild-type mice. In mceph/mceph brains, we found upregulation of IGF binding proteins (BP)-2, -4, -5, and -6 mRNA, the regulating hormone transforming growth factor (TGF)beta1 mRNA and also a local downregulation of IGFBP-5 mRNA compared to wild-type brains by in situ hybridization. The altered expression of these mRNA species is colocalized in cerebral cortex, hippocampus, amygdala and piriform/entorhinal cortex. The mceph/mceph mice express less of the myelin component proteolipid protein (PLP) mRNA in corpus callosum. No expression difference of the housekeeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in brain or IGF system components in liver was found between mceph/mceph and wild-type mice. These data suggest that the IGF system has an important role in the excessive growth of the mceph/mceph brains.

Glial fibrillary acidic protein (GFAP): modulation by growth factors and its implication in astrocyte differentiation

Intermediate filament (IF) proteins constitute an extremely large multigene family of developmentally and tissue-regulated cytoskeleton proteins abundant in most vertebrate cell types. Astrocyte precursors of the CNS usually express vimentin as the major IF. Astrocyte maturation is followed by a switch between vimentin and glial fibrillary acidic protein (GFAP) expression, with the latter being recognized as an astrocyte maturation marker. Levels of GFAP are regulated under developmental and pathological conditions. Upregulation of GFAP expression is one of the main characteristics of the astrocytic reaction commonly observed after CNS lesion. In this way, studies on GFAP regulation have been shown to be useful to understand not only brain physiology but also neurological disease. Modulators of GFAP expression include several hormones such as thyroid hormone, glucocorticoids and several growth factors such as FGF, CNTF and TGF beta, among others. Studies of the GFAP gene have already identified several putative growth factor binding domains in its promoter region. Data obtained from transgenic and knockout mice have provided new insights into IF protein functions. This review highlights the most recent studies on the regulation of IF function by growth factors and hormones.

Simultaneous analysis of multiple gene expression patterns as a function of development, injury or senescence

Concurrent changes in expression of eight genes were examined following cryogenic rat brain injury. Cortical RNA levels were catalogued at time 0, and at 1 h and 1 week following injury. The genes include thymidine kinase (TK), c-fos, renin, myelin basic protein (MBP), proteolipid protein (PLP), glial fibrillary acidic protein (GFAP), insulin-like growth factor-1 (IGF-1), and somatostatin. All demonstrate increased expression following injury. Renin and c-fos exhibit detectable changes as early as 1 h post-injury.