Chemokine antagonist infusion promotes axonal sparing after spinal cord contusion injury in rat

Spinal cord injury produced by mechanical contusion causes the onset of acute and chronic degradative events. These include blood brain barrier disruption, edema, demyelination, axonal damage and neuronal cell death. Posttraumatic inflammation after spinal cord injury has been implicated in the secondary injury that ultimately leads to neurologic dysfunction. Studies after spinal cord contusion have shown expression of several chemokines early after injury and suggested a role for them in the ordered recruitment of inflammatory cells at the lesion site (McTigue et al. [1998] J. Neurosci. Res. 53:368-376; Lee et al., [2000] Neurochem Int). We have demonstrated previously that infusion of the broad-spectrum chemokine receptor antagonist (vMIPII) in the contused spinal cord initially attenuates leukocyte infiltration, suppresses' gliotic reaction and reduces neuronal damage after injury. These changes are accompanied by increased expression of bcl-2, the endogenous apoptosis inhibitor, and reduced neuronal apoptosis (Ghirnikar et al. [2000] J. Neurosci. Res. 59:63-73). We demonstrate that 2 and 4 weeks of vMIPII infusion in the contusion-injured spinal cord also results in decreased hematogenous infiltration and is accompanied by reduced axonal degeneration in the gray matter. Luxol fast blue and MBP immunoreactivity indicated reduced myelin breakdown in the dorsal and ventral funiculi. Increased neuronal survival in the ventral horns of vMIPII infused cords was seen along with increased bcl-2 staining in them. Immunohistochemical identification of fiber phenotypes showed increased presence of calcitonin gene related peptide, choline acetyl transferase and tyrosine hydroxylase positive fibers as well as increased GAP43 staining in treated cords. These results suggest that sustained reduction in posttraumatic cellular infiltration is beneficial for tissue survival. A preliminary report of this study has been published (Eng et al. [2000] J. Neurochem. 74(Suppl):S67B). In contrast to vMIPII, infusion of MCP-1 (9-76), a N-terminal analog of the MCP-1 chemokine showed only a modest reduction in cellular infiltration at 14 and 21 dpi without significant tissue survival after spinal cord contusion injury. Comparing data on tissue survival obtained with vMIPII and MCP-1 (9-76) further validate the importance of the use of broad-spectrum antagonists in the treatment of spinal cord injury. Controlling the inflammatory reaction and providing a growth permissive environment would enhance regeneration and ultimately lead to neurological recovery after spinal cord injury. J. Neurosci. Res. 64:582-589, 2001. Published 2001 Wiley-Liss, Inc.

Glial fibrillary acidic protein: GFAP-thirty-one years (1969-2000)

It is now well established that the glial fibrillary acidic protein (GFAP) is the principal 8-9 nm intermediate filament in mature astrocytes of the central nervous system (CNS). Over a decade ago, the value of GFAP as a prototype antigen in nervous tissue identification and as a standard marker for fundamental and applied research at an interdisciplinary level was recognized (Raine, 135). As a member of the cytoskeletal protein family, GFAP is thought to be important in modulating astrocyte motility and shape by providing structural stability to astrocytic processes. In the CNS of higher vertebrates, following injury, either as a result of trauma, disease, genetic disorders, or chemical insult, astrocytes become reactive and respond in a typical manner, termed astrogliosis. Astrogliosis is characterized by rapid synthesis of GFAP and is demonstrated by increase in protein content or by immunostaining with GFAP antibody. In addition to the major application of GFAP antisera for routine use in astrocyte identification in the CNS, the molecular cloning of the mouse gene in 1985 has opened a new and rich realm for GFAP studies. These include antisense, null mice, and numerous promoter studies. Studies showing that mice lacking GFAP are hypersensitive to cervical spinal cord injury caused by sudden acceleration of the head have provided more direct evidence for a structural role of GFAP. While the structural function of GFAP has become more acceptable, the use of GFAP antibodies and promoters continue to be valuable in studying CNS injury, disease, and development.

Cytokine chemokine expression in contused rat spinal cord

Spinal cord injury within the first few hours, is complicated by inflammatory mechanisms, including the influx of monocyte/macrophages as well as the activation of resident spinal microglia and astrocytes. Numerous studies have suggested that the initial infiltration of the hematogenous cells may be due to the secretion of cytokines and chemokines in the injured CNS. In order to elucidate which chemotactic factors may be expressed following traumatic spinal cord contusion, the presence of mRNA for a number of cytokines, chemokines and growth factors was examined in contused rat spinal cord by reverse transcriptase-polymerase chain reaction and immunohistochemistry. Spinal injury was accompanied by an increase in glial fibrillary acidic protein mRNA suggesting astrocyte activation and astrogliosis. TNFalpha message levels were upregulated as early as 1 h post injury and returned to baseline levels by 3 days post injury (DPI). By immunocytochemistry, staining for TNFalpha increased at 1 and 3 dpi and was predominantly diffuse in the necrotic tissue. The chemokines IP-10, MCP-1, and MIP-1alpha were also detected in the injured spinal cord. mRNA levels of IP-10 peaked around 6 h post injury and were upregulated up to 7 dpi. MCP-1 mRNA was detected at 1 h post injury and its levels returned to baseline by 14 dpi. An increase in MCP-1 staining was observed from 1 to 7 dpi. The staining was also diffuse in the necrotic tissue and also localized to cells near the site of injury. The presence of aFGF and bFGF was also detected in the injured spinal cord. mRNA for aFGF was detected at 0 time, increased at 6 h post injury, peaked at 3 days, and remained elevated up to 21 days. bFGF mRNA was initially detected at 1 h post injury, increased between 6 h and 3 days, declined thereafter and returned to baseline levels by 21 days.

Chemokine antagonist infusion attenuates cellular infiltration following spinal cord contusion injury in rat

Spinal cord injury is accompanied by an initial inflammatory reaction followed by secondary injury that is caused, in part, by apoptosis. Recruitment of leukocytes from the blood compartment to the site of inflammation in the injured spinal cord has been attributed to locally generated chemotactic agents (cytokines and chemokines). In addition to upregulation in the message levels of a number of chemokines, we have found up-regulation in the message levels of several chemokine receptors following spinal cord contusion injury. To reduce the inflammatory response after spinal cord injury, we have blocked the interaction of chemokine receptors with their ligands using the vMIPII chemokine antagonist. Using a rat model of spinal cord contusion injury, we show that continuous infusion of the antagonist for up to 7 days results in a decrease in infiltrating hematogenous cells at the site of injury. Histological evaluation ofthe tissue showed fewer activated macrophages at the site of injury. Concomitantly, reduced neuronal loss and gliosis were observed in the antagonist infused spinal cord. In addition, increased expression of Bcl-2 gene, an endogenous inhibitor of apoptosis, was seen in the antagonist infused spinal cord at 7 days post injury. Morphologically, staining with the bisbenzamide dye Hoechst 33342 showed significantly more apoptotic bodies in the vehicle compared to antagonist infused spinal cord. Our data suggest that chemokine antagonist infusion post-injury results in limiting the inflammatory response following spinal cord contusion injury, thereby attenuating neuronal loss, possibly due to decreased apoptosis. These findings support the contention that disrupting chemokine interactions with their receptors may be an effective approach in reducing the secondary damage after spinal cord injury.

Chemokine inhibition in rat stab wound brain injury using antisense oligodeoxynucleotides

Traumatic injury to the central nervous system (CNS) results in the breakdown of the blood-brain barrier and recruitment of hematogenous cells at the site of injury. The role of chemokines in this process has been well recognized and they have been regarded as promising targets for development of anti-inflammatory therapies. The expression of monocyte chemoattractant protein (MCP-1), in particular, has been closely linked to macrophage infiltration following trauma in rat brain. In this study we determined whether inhibition of MCP-1 following stab wound injury would reduce macrophage infiltration. Stab wound injured Sprague-Dawley rats were infused with MCP-1 sense or antisense oligonucleotides using an Alzet miniosmotic pump (1 microl/h for 3 days). Three days following injury, widespread gliosis was observed in both groups of rats as judged by glial fibrillary acidic protein (GFAP) immunoreactivity. Immunohistochemistry showed significantly less staining for MCP-1 in antisense treated animals. In addition, the number of macrophages were reduced by 30% in the antisense compared to the sense treated animals (P < 0.05). These results demonstrate that modulation of MCP-1 expression in stab wound injury directly affects monocytic infiltration and provide a basis for MCP-1 inhibition as a therapeutic strategy for controlling inflammatory events of traumatic brain injury.

Inflammation in traumatic brain injury: role of cytokines and chemokines

A traumatic injury to the adult mammalian central nervous system (CNS), such as a stab wound lesion, results in reactive astrogliosis and the migration of hematogenous cells into the damaged neural tissue. The roles of cytokines and growth factors released locally by the damaged endogenous cells are recognized in controlling the cellular changes that occur following CNS injury. However, the role of chemokines, a novel class of chemoattractant cytokines, is only recently being studied in regulating inflammatory cell invasion in the injured/diseased CNS (1). The mRNAs for several chemokines have been shown to be upregulated in experimental allergic encephalomyelitis (EAE), an inflammatory demyelinating disease of the CNS, but chemokine expression in traumatic brain injury has not been studied in detail. Astrocytes have been demonstrated to participate in numerous processes that occur following injury to the CNS. In particular, astrocytic expression of cytokines and growth factors in the injured CNS has been well reviewed (2). Recently a few studies have detected the presence of chemokines in astrocytes following traumatic brain injury (3,4). These studies have suggested that chemokines may represent a promising target for future therapy of inflammatory conditions. This review summarizes the events that occur in traumatic brain injury and discusses the roles of resident and non-resident cells in the expression of growth factors, cytokines and chemokines in the injured CNS.

Chemokine expression in rat stab wound brain injury

A traumatic injury to the adult mammalian central nervous system (CNS) results in reactive astrogliosis and the migration of hematogenous cells into the damaged neural tissue. Chemokines, a novel class of chemoattractant cytokines, are now being recognized as mediators of the inflammatory changes that occur following injury. The expression of MCP-1 (macrophage chemotactic peptide-1), a member of the beta family of chemokines, has recently been demonstrated in trauma in the rat brain (Berman et al.: J Immunol 156:3017-3023, 1996). Using a stab wound model for mechanical injury, we studied the expression of two other beta chemokines: RANTES (Regulated on Activation, Normal T cell Expressed and Secreted) and MIP-1 beta (macrophage inflammatory protein-1 beta) in the rat brain. The stab wound injury was characterized by widespread gliosis and infiltration of hematogenous cells. Immunohistochemical staining revealed the presence of RANTES and MIP-1 beta in the injured brain. RANTES and MIP-1 beta were both diffusely expressed in the necrotic tissue and were detected as early as 1 day post-injury (dpi). Double-labeling studies showed that MIP-1 beta, but not RANTES, was expressed by reactive astrocytes near the lesion site. In addition, MIP-1 beta staining was also detected on macrophages at the site of injury. The initial expression of the chemokines closely correlated with the appearance of inflammatory cells in the injured CNS, suggesting that RANTES and MIP-1 beta may play a role in the inflammatory events of traumatic brain injury. This study also demonstrates for the first time MIP-1 beta expression in reactive astrocytes following trauma to the rat CNS.

Astrocytoma and Schwann cells in coculture

Glial fibrillary acidic protein (GFAP) is the principal intermediate filament protein found in mature astrocytes. Although the exact function of GFAP is poorly understood, it is presumed to stabilize the astrocyte's cytoskeleton and help in maintaining cell shape. Previous studies from our laboratory have shown that when astrocytes were cocultured with primary Schwann cells (pSCs), astrocytes became hypertrophied and fibrous with intensely positive GFAP staining and segregated Schwann cells (SCs) into pockets. In order to understand the functional role of GFAP in this already established astrocyte-SC coculture model, we generated GFAP-negative cell lines from a GFAP-positive astrocytoma cell line and cocultured both the cell lines with pSCs. Our studies demonstrate that the GFAP-positive cell line put out processes toward the SCs, whereas the GFAP-negative cells did not form processes and the majority of the cells remained round. The most significant and interesting finding of this study, however, is the formation of elaborate processes by SCs when grown in coculture with the astrocytoma cells, unlike SCs cultured alone, which showed their typical bipolar spindle-shaped morphology. The extent of processes did not seem to be dependent of GFAP, since SCs cultured with both the cell lines formed similar processes. This coculture model may be useful in elucidating the factor(s) responsible for the formation of processes by SCs and can be further help in our understanding of the mechanism of morphological transformation of SCs.

Astrocyte-astrocytoma cell line interactions in culture

Astrocytomas are the most common brain tumors arising in the CNS and account for 65% of all primary brain tumors. Astrocytes have been shown to have the highest predisposition to malignant transformation compared to any other CNS cell type. The majority of astrocytomas are histologically malignant neoplasm. Previous studies have shown that resident astrocytes are the first cell type to react to tumors and surround them. However, the role of these astrocytes in tumor formation and progression has not been determined. In the present study, we have co-cultured astrocytes with a permanent cell line S635c15 (derived from anaplastic astrocytoma) in order to understand the cellular interactions between astrocytes and astrocytoma cells. Our studies demonstrate that astrocytes in contact with the tumor cells become reactive and fibrous with an increase in glial fibrillary acidic protein (GFAP) immunoreactivity as early as 4 days in culture. By 8 days, astrocytes formed glial boundaries around the tumor cells which grew as round colonies. The astrocytic processes surrounding the tumor cells were also intensely GFAP positive. Since the behavior of these cells observed in culture is very similar to their interaction seen in vivo, this co-culture system may serve as an in vitro model for astrocyte and astrocytoma cell line interaction and aid in our understanding of the molecular and cellular mechanisms during early stages of tumor formation and cell interactions.

Inflammation in EAE: role of chemokine/cytokine expression by resident and infiltrating cells

Experimental allergic encephalomyelitis (EAE) is an inflammatory demyelinating disease of the central nervous system (CNS) which has many clinical and pathological features in common with multiple sclerosis (MS). Comparison of the histopathology of EAE and MS reveals a close similarity suggesting that these two diseases share common pathogenetic mechanisms. Immunologic processes are widely accepted to contribute to the initiation and continuation of the diseases and recent studies have indicated that microglia, astrocytes and the infiltrating immune cells have separate roles in the pathogenesis of the MS lesion. The role of cytokines as important regulatory elements in these immune processes has been well established in EAE and the presence of cytokines in cells at the edge of MS lesions has also been observed. However, the role of chemokines in the initial inflammatory process as well as in the unique demyelinating event associated with MS and EAE has only recently been examined. A few studies have detected the transient presence of selected chemokines at the earliest sign of leukocyte infiltration of CNS tissue and have suggested astrocytes as their cellular source. Based on these studies, chemokines have been postulated as a promising target for future therapy of CNS inflammation. This review summarized the events that occur during the inflammatory process in EAE and discusses the roles of cytokine and chemokine expression by the resident and infiltrating cells participating in the process.

Chondroitin sulfate proteoglycan staining in astrocyte-Schwann cell co-cultures

Transplantation of Schwann cells (SCs) in the central nervous system (CNS) for remyelination in pathological situations has been considered a promising approach. However, numerous studies have indicated that astrocytes have a restrictive effect on SC migration within the CNS. We have previously established an in vitro model which demonstrates the restrictive effect of astrocytes on SCs (Ghirnikar and Eng, Glia 4:367-377, 1994). Using this culture model, in the present study, we have characterized the molecular basis underlying astrocyte-SC interaction and demonstrated chondroitin sulfate proteoglycan (CSP) staining in the co-cultures. Following 1-2 weeks of incubation, CSP staining was specifically associated with SCs co-cultured with astrocytes. Staining with antibodies specific for the different chondroitin sulfate isomers revealed the presence of both, chondroitin-4- and 6-sulfates in SCs. In contrast, SCs when cultured alone, or in the presence of astrocytes conditioned medium did not show CSP staining. These data suggest that CSP staining is associated with SCs following co-culture with astrocytes and mediated by cell to cell contact. We hypothesize that the CSP, alone or in combination with other molecules expressed by astrocytes and/or SCs, may be involved in the restrictive effects of astrocytes on SCs. Identification of molecules involved in the unfavorable interaction between astrocytes and SCs will have an important bearing on efforts to remyelinate demyelinated axons by SC transplantation within the damaged CNS.

Astrocyte-Schwann cell interactions in culture

After injury, either as a result of trauma or degenerating/demyelinating diseases, axons of the central nervous system (CNS) normally fail to regenerate. Transplantation of glial cells, particularly Schwann cells, into areas of injury or demyelination has been considered a promising approach to promote recovery. However, the extent of Schwann cell interaction with CNS axons is greatly influenced by the presence of astrocytes which redefine the CNS-PNS (peripheral nervous system) boundary in a lesioned CNS, thereby preventing invasion of Schwann cells. The molecular basis for this restrictive effect of astrocytes on Schwann cells is not known. In the present study, we have cocultured astrocytes and Schwann cells to develop an in vitro model to characterize this interaction. Astrocytes in contact with Schwann cells appeared hypertrophied and showed increased staining for glial fibrillary acidic protein (GFAP). In cocultures maintained for 2-3 weeks, segregation of the two cell types was observed, Schwann cells appeared in groups, and each group was surrounded and separated from one another by astrocytic processes. Since the behavior of these two cell types observed in culture is very similar to their interaction seen in vivo, this coculture model may be useful in further studying the relationship between astrocytes and Schwann cells.

Astrogliosis in culture: III. Effect of recombinant retrovirus expressing antisense glial fibrillary acidic protein RNA

Injury to the central nervous system (CNS) either from trauma or due to demyelinating/degenerating diseases results in a typical response of astrocytes, termed astrogliosis. This reaction is characterized by astrocyte proliferation, extensive hypertrophy of nuclei, cell body, and cytoplasmic processes and an increase in immunodetectable glial fibrillary acidic protein (GFAP). GFAP accumulation may cause a physical barrier preventing the reestablishment of a functional environment. Our studies have aimed at modulating astrogliosis by inhibiting or delaying GFAP synthesis in damaged and reactive astrocytes. The present study investigates the use of a recombinant retrovirus expressing antisense GFAP RNA in controlling the response of mechanically injured astrocytes. A 650 bp fragment from the coding region of mouse GFAP cDNA was cloned in the antisense orientation under the control of long terminal repeat (LTR) promoter of Moloney murine leukemia virus. Increase in GFAP as detected by immunocytochemical staining in injured astrocytes was inhibited by treatment with retrovirus expressing antisense GFAP RNA. Also, astrocytes at the site of injury in these scratched cultures did not show cell body hypertrophy compared to control cultures. These observations demonstrate that the increase in GFAP at the site of injury can be inhibited using retroviral treatment and indicate the potential of retrovirus-mediated gene transfer in modulating scar formation in the CNS in vivo. These studies also shed light on the role of GFAP in maintaining the morphology of astrocytes.

GFAP and astrogliosis

One of the most remarkable characteristics of astrocytes is their vigorous response to diverse neurologic insults, a feature that is well conserved across a variety of different species. The astroglial response occurs rapidly and can be detected within one hour of a focal mechanical trauma (Mucke et al., 1991). Prominent reactive astrogliosis is seen; in AIDS dementia; a variety of other viral infections; prion associated spongiform encephalopathies; inflammatory demyelinating diseases; acute traumatic brain injury; neurodegenerative diseases such as Alzheimer's disease. The prominence of astroglial reactions in various diseases, the rapidity of the astroglial response and the evolutionary conservation of reactive astrogliosis indicate that reactive astrocytes fulfill important functions of the central nervous system (CNS). Yet, the exact role reactive astrocytes play in the injured CNS has so far remained elusive. This chapter summaries the various experimental models and diseases that exhibit astrogliosis and increase in glial fibrillary acidic protein (GFAP). Recent in vitro studies to inhibit GFAP synthesis are also presented.