Quality assessment of Rheum species cultivated in Japan by focusing on M2 polarization of microglia.

In traditional Japanese medicine, Rhei Rhizoma is used as a purgative, blood stasis-resolving and antipsychotic drug. The latter two properties are possibly related to anti-inflammatory effects. Microglia regulate inflammation in the central nervous system. M1 microglia induce inflammation, while M2 microglia inhibit inflammation and show neurotrophic effects. This study investigated the effects from water extracts of roots of cultivated Rheum species in Nagano Prefecture, Japan (strain C, a related strain to a Japanese cultivar, 'Shinshu-Daio'; and strain 29, a Chinese strain) and 3 kinds of Rhei Rhizoma available in the Japanese market, and also examined their constituents on the polarization of cultured microglia. All extracts significantly decreased M1 microglia, and strains C and 29 significantly increased M2 microglia. Furthermore, the extracts of both strains significantly increased the M2/M1 ratio. Among the constituents of Rhei Rhizoma, ( +)-catechin (2), resveratrol 4'-O-ß-D-(6″-O-galloyl) glucopyranoside (5), isolindleyin (8), and physcion (15) significantly increased the M2/M1 ratio. The contents of the constituents in water extract of each strain were quantified using HPLC. The extracts of strains C and 29 contained relatively large amounts of 2 and 5; and 2, 8, and 15, respectively. This study showed the water extracts of roots of cultivated Rheum strains in Japan had the effects of M2 polarization of microglia, suggesting that these strains become the candidate to develop anti-inflammatory Rhei Rhizoma. Moreover, the suitable chemical composition to possess anti-inflammatory activity in the brain was clarified for the future development of new type of Rhei Rhizoma.

Shati/Nat8l Overexpression Improves Cognitive Decline by Upregulating Neuronal Trophic Factor in Alzheimer's Disease Model Mice.

Alzheimer's disease (AD) is a type of dementia characterized by the deposition of amyloid ß, a causative protein of AD, in the brain. Shati/Nat8l, identified as a psychiatric disease related molecule, is a responsive enzyme of N-acetylaspartate (NAA) synthesis. In the hippocampi of AD patients and model mice, the NAA content and Shati/Nat8l expression were reported to be reduced. Having recently clarified the involvement of Shati/Nat8l in cognitive function, we examined the recovery effect of the hippocampal overexpression of Shati/Nat8l in AD model mice (5XFAD). Shati/Nat8l overexpression suppressed cognitive dysfunction without affecting the Aß burden or number of NeuN-positive neurons. In addition, brain-derived neurotrophic factor mRNA was upregulated by Shati/Nat8l overexpression in 5XFAD mice. These results suggest that Shati/Nat8l overexpression prevents cognitive dysfunction in 5XFAD mice, indicating that Shati/Nat8l could be a therapeutic target for AD.

Recovery from spinal cord injury via M2 microglial polarization induced by Polygalae Radix.

BACKGROUND: Spinal cord injury (SCI) is a refractory neurodegenerative disease caused by inflammation. M1 microglia induce inflammation, whereas M2 suppress inflammation and exhibit neuroprotective effects. Following SCI, M1 cells are more predominant than M2 cells, and hence, increasing the predominance of M2 microglia may improve SCI. PURPOSE: We aimed to evaluate the active constituents of herbal medicine that induce M2 predominance and to investigate their effects using SCI model mice. METHODS: Herbal medicine inducing M2 were screened using cultured microglia. After orally administering the active herbal medicine, Polygalae Radix (PR), to SCI model mice, motor function was evaluated. Compounds in the spinal cord following treatment were assessed using liquid chromatography-mass spectrometry. The effects of compounds detected in the spinal cord were investigated in cultured microglia. RESULTS: PR induced M2 predominance in cultured microglia, improved motor function in SCI model mice, and showed a tendency to increase M2 microglia and protect against axonal degeneration in the inured spinal cord. Sibiricose A5 and 3,6'-disinapoyl sucrose were identified as active constituents in PR. CONCLUSION: PR may be a promising candidate for the treatment of SCI by inducing M2 predominance.

Trigonelline recovers memory function in Alzheimer's disease model mice: evidence of brain penetration and target molecule.

Trigonelline (TGN; 1-methylpyridin-1-ium-3-carboxylate) is a widely distributed alkaloid derived from plants. Since we previously found a neurite outgrowth effect of TGN, we hypothesised that TGN might help to improve memory deficits. Here, the efficacy of TGN in restoring amyloid ß (Aß)-induced axonal degeneration and in improving memory function was investigated in Alzheimer's disease 5XFAD model mice that overexpress mutated APP and PS1 genes. Exposure of Aß25-35 for 3 days induced atrophy of axons and dendrites. Post treatment of TGN recovered the lengths of axons and dendrites. Following oral administration of TGN in mice, TGN itself was detected in the plasma and cerebral cortex. Oral administration of TGN to 5XFAD mice for 14 days showed significant improvement in object recognition memory (P < 0.001) and object location memory (P < 0.01). TGN administration also normalised neurofilament light levels in the cerebral cortex (P < 0.05), which is an axonal damage-associated biomarker. Analysis of target proteins of TGN in neurons by a drug affinity responsive target stability (DARTS) method identified that creatine kinase B-type (CKB) is a direct binding protein of TGN. Treatment with a CKB inhibitor cancelled the TGN-induced axonal and dendritic growth. In conclusion, we found for the first time that TGN penetrates the brain and may activate CKB, leading to axonal formation. This study shows the potential of TGN as a new drug candidate, and a new target molecule, CKB, in memory recovery signalling.

Natural Medicines and Their Underlying Mechanisms of Prevention and Recovery from Amyloid Β-Induced Axonal Degeneration in Alzheimer's Disease.

In Alzheimer's disease (AD), amyloid ß (Aß) induces axonal degeneration, neuronal network disruption, and memory impairment. Although many candidate drugs to reduce Aß have been clinically investigated, they failed to recover the memory function in AD patients. Reportedly, Aß deposition occurred before the onset of AD. Once neuronal networks were disrupted by Aß, they could hardly be recovered. Therefore, we speculated that only removal of Aß was not enough for AD therapy, and prevention and recovery from neuronal network disruption were also needed. This review describes the challenges related to the condition of axons for AD therapy. We established novel in vitro models of Aß-induced axonal degeneration. Using these models, we found that several traditional medicines and their constituents prevented or helped recover from Aß-induced axonal degeneration. These drugs also prevented or helped recover from memory impairment in in vivo models of AD. One of these drugs ameliorated memory decline in AD patients in a clinical study. These results indicate that prevention and recovery from axonal degeneration are possible strategies for AD therapy.

GRP78-Mediated Signaling Contributes to Axonal Growth Resulting in Motor Function Recovery in Spinal Cord-Injured Mice.

Promoting axonal growth is essential for repairing damaged neuronal connections and motor function in spinal cord injury (SCI). Neuroleukin (NLK) exerts axonal growth activity in vitro and in vivo, but the mechanism remains unclear. This study reveals that the 78-kDa glucose-regulated protein (GRP78) is a NLK neuronal receptor that contributes to recovery from SCI. Binding and immunoprecipitation assays indicated that NLK binds to GRP78. Pretreatment to cultured neurons with a GRP78-neutralizing antibody suppressed NLK-induced axonal growth. Blocking cell surface GRP78 inhibited neuronal NLK-induced Akt activation. Treatment with an Akt inhibitor suppressed NLK-induced axonal growth. Continuous administration of NLK into the lateral ventricle of SCI mice increased axonal density in the injured region and restored motor function, which was not observed when NLK was simultaneously administered with a GRP78-neutralizing antibody. These results indicate that GRP78 regulates the NLK-induced axonal growth activity; NLK-GRP78 signaling promotes motor function recovery in SCI, presenting as a potential therapeutic target.

Combined Treatment with Two Water Extracts of Eleutherococcus senticosus Leaf and Rhizome of Drynaria fortunei Enhances Cognitive Function: A Placebo-Controlled, Randomized, Double-Blind Study in Healthy Adults.

We previously found that the water extract of Eleutherococcus senticosus leaves (ES extract) enhanced cognitive function in normal mice. Our study also revealed that the water extract of rhizomes of Drynaria fortunei (DR extract) enhanced memory function in Alzheimer's disease model mice. In addition, our previous experiments suggested that a combined treatment of ES and DR extracts synergistically improved memory and anti-stress response in mice. Although those two botanical extracts are expected to be beneficial for neuropsychological function, no clinical data has ever been reported. Therefore, we performed a placebo-controlled, randomized, double-blind study to evaluate cognitive enhancement and anti-stress effects by the intake of a combined extract in healthy volunteers. The intake period was 12 weeks. The Japanese version of the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) test was used for neurocognitive assessment. The combined treatment of ES and DR extracts significantly increased the figure recall subscore of RBANS (p = 0.045) in an intergroup comparison. Potentiation of language domain ((p = 0.040), semantic fluency (p = 0.021) and figure recall (p = 0.052) was shown by the extracts (in intragroup comparison). In anti-stress response, the anxiety/uncertainly score was improved by the extract in an intragroup comparison (p = 0.022). No adverse effects were observed. The combined treatment of ES and DR extracts appear to safely enhance a part of cognitive function in healthy adults.

Cistanche tubulosa (Schenk) Wight Extract Enhances Hindlimb Performance and Attenuates Myosin Heavy Chain IId/IIx Expression in Cast-Immobilized Mice.

Skeletal muscle atrophy is encountered in many clinical conditions, but a pharmacological treatment has not yet been established. Cistanche tubulosa (Schenk) Wight is an herbal medicine used in traditional Japanese and Chinese medicine. In the current study, we investigated the effect of C. tubulosa extract (CTE) on atrophied muscle in vivo. We also investigated hindlimb cast immobilization in mice and devised a novel type of hindlimb-immobilizing cast, consisting of sponge-like tape and a thin plastic tube. Using this method, 3 out of 4 groups of mice (n = 11 for each group) were cast-immobilized in the hindlimbs and administered CTE or vehicle for 13 days. A sham procedure was performed in the mice of the fourth group to which the vehicle was administered. Next, the triceps surae muscles (TS) were excised. To analyze the effect of the novel cast system and CTE administration on muscle atrophy, we evaluated TS wet weight and myofiber cross-sectional area (CSA). We also determined MyHC IId/IIx expression levels by western blotting, since their increase is a hallmark of disuse muscle atrophy, suggesting slow-to-fast myofiber type shift. Moreover, we performed two tests of hindlimb performance. The novel cast immobilization method significantly reduced TS wet weight and myofiber CSA. This was accompanied by deterioration of hindlimb function and an increase in MyHC IId/IIx expression. CTE administration did not alter TS wet weight or myofiber CSA; however, it showed a trend of amelioration of the loss of hindlimb function and of suppression of the increased MyHC IId/IIx expression in cast-immobilized mice. Our novel hindlimb cast immobilization method effectively induced muscle atrophy. CTE did not affect muscle mass, but suppressed the shift from slow to fast myofiber type in cast-immobilized mice, ameliorating hindlimb function deterioration.

[Development of New Therapies for Neurodegenerative Diseases via Axonal Growth].

In neurodegenerative diseases, such as Alzheimer's disease (AD) and spinal cord injury (SCI), inhibited axonal regeneration lead to irreversible functional impairment. Although many agents that eliminate axonal growth impediments have been clinically investigated, none induced functional recovery. I hypothesized that the removal of impediments alone was not enough and that promoting axonal growth and neuronal network reconstruction were needed for recovery from neurodegenerative diseases. To promote axonal growth, I have focused on neurons and microglia. In vitro models of AD and SCI were developed by culturing neurons in the presence of amyloid ß (Aß) and chondroitin sulfate proteoglycan, respectively. These were then used to identify several extracts of herbal medicines and their constituents that promoted axonal growth. Oral administration of these extracts and their constituents improved memory and motor function in in vivo mouse models of AD and SCI, respectively. The bioactive compounds in these extracts were identified by analyzing brain and spinal cord samples from the mice. Their protein targets were identified using the drug affinity responsive target stability method. Analysis of early events in the axons after culture with Aß revealed that the inhibition of endocytosis was sufficient to prevent the axonal atrophy and memory deficits caused by Aß. The compounds that increased M2 microglia were observed to promote axonal normalization and growth; they were also found to recover memory and motor function in mice models of AD and SCI, respectively. The above results indicate that axonal growth plays important roles in the recovery from AD and SCI.

Matrine promotes neural circuit remodeling to regulate motor function in a mouse model of chronic spinal cord injury.

In chronic phase of spinal cord injury, functional recovery is more untreatable compared with early intervention in acute phase of spinal cord injury. In the last decade, several combination therapies successfully improved motor dysfunction in chronic spinal cord injury. However, their effectiveness is not sufficient. We previously found a new effective compound for spinal cord injury, matrine, which induced axonal growth and functional recovery in acute spinal cord injury mice via direct activation of extracellular heat shock protein 90. Although our previous study clarified that matrine was an activator of extracellular heat shock protein 90, the potential of matrine for spinal cord injury in chronic phase has not been sufficiently evaluated. Thus, this study aimed to investigate whether matrine ameliorates chronic spinal cord injury in mice. Once daily intragastric administration of matrine (100 µmol/kg per day) to spinal cord injury mice were starte at 28 days after injury, and continued for 154 days. Continuous matrine treatment improved hindlimb motor function in chronic spinal cord injury mice. In injured spinal cords of the matrine-treated mice, the density of neurofilament-H-positive axons was increased. Moreover, matrine treatment increased the density of bassoon-positive presynapses in contact with choline acetyltransferase-positive motor neurons in the lumbar spinal cord. These findings suggest that matrine promotes remodeling and reconnection of neural circuits to regulate hindlimb movement. All protocols were approved by the Committee for Animal Care and Use of the Sugitani Campus of the University of Toyama (approval No. A2013INM-1 and A2016INM-3) on May 7, 2013 and May 17, 2016, respectively.

Memory Enhancement by Oral Administration of Extract of Eleutherococcus senticosus Leaves and Active Compounds Transferred in the Brain.

The pharmacological properties of Eleutherococcus senticosus leaf have not been clarified although it is taken as a food item. In this study, the effects of water extract of Eleutherococcus senticosus leaves on memory function were investigated in normal mice. Oral administration of the extract for 17 days significantly enhanced object recognition memory. Compounds absorbed in blood and the brain after oral administration of the leaf extract were detected by LC-MS/MS analyses. Primarily detected compounds in plasma and the cerebral cortex were ciwujianoside C3, eleutheroside M, ciwujianoside B, and ciwujianoside A1. Pure compounds except for ciwujianoside A1 were administered orally for 17 days to normal mice. Ciwujianoside C3, eleutheroside M, and ciwujianoside B significantly enhanced object recognition memory. These results demonstrated that oral administration of the leaf extract of E. senticosus enhances memory function, and that active ingredients in the extract, such as ciwujianoside C3, eleutheroside M, and ciwujianoside B, were able to penetrate and work in the brain. Those three compounds as well as the leaf extract had dendrite extension activity against primary cultured cortical neurons. The effect might relate to memory enhancement.

Naringenin promotes microglial M2 polarization and Aß degradation enzyme expression.

Two kinds of microglia are known, classical M1 and alternative M2 phenotypes. Amyloid ß (Aß), a critical cause of Alzheimer's disease (AD), promotes M1 microglial polarization, leading to neuroinflammation and neuronal death. M2 microglia play important roles in anti-inflammatory effects, Aß clearance, and memory recovery in AD. Therefore, increasing of M2 microglia is expected to recover from AD. We previously found that naringenin, a blood-brain barrier penetrating compound, decreased Aß deposits and recovers memory function in transgenic AD model mice. Naringenin reportedly showed anti-inflammatory properties. Here, we aim to investigate potential effects of naringenin on microglial polarization and to reveal the underlying mechanisms of Aß reduction. Primary cultured cortical microglia were treated with Aß1-42 , following administration of naringenin. Naringenin remarkably promoted M2 microglia polarization and inhibited Aß1-42 -induced M1 microglia activation. Because microglia reportedly played a critical role in cerebral Aß clearance through Aß degradation enzymes after phagocytosis, we investigated the expression of Aß degradation enzymes, such as neprilysin and insulin degradation enzyme. After naringenin treatment, these Aß degradation enzymes were downregulated in M1 microglia and upregulated in M2 microglia. Taken together, our results showed that naringenin increased Aß degradation enzymes in M2 microglia, probably leading to Aß plaque reduction.

Visualizing Axonal Growth Cone Collapse and Early Amyloid ß Effects in Cultured Mouse Neurons.

Amyloid-ß (Aß) causes memory impairments in Alzheimer's disease (AD). Although therapeutics have been shown to reduce Aß levels in the brains of AD patients, these do not improve memory functions. Since Aß aggregates in the brain before the appearance of memory impairments, targeting Aß may be inefficient for treating AD patients who already exhibit memory deficits. Therefore, downstream signaling due to Aß deposition should be blocked before AD development. Aß induces axonal degeneration, leading to the disruption of neuronal networks and memory impairments. Although there are many studies on the mechanisms of Aß toxicity, the source of Aß toxicity remains unknown. To help identify the source, we propose a novel protocol that uses microscopy, gene transfection, and live cell imaging to investigate early changes caused by Aß in axonal growth cones of cultured neurons. This protocol revealed that Aß induced clathrin-mediated endocytosis in axonal growth cones followed by growth cone collapse, demonstrating that inhibition of endocytosis prevents Aß toxicity. This protocol will be useful in studying the early effects of Aß and may lead to more efficient and preventative AD treatment.

Extracellular Neuroleukin Enhances Neuroleukin Secretion From Astrocytes and Promotes Axonal Growth in vitro and in vivo.

Under pathological conditions in the central nervous system (CNS), including spinal cord injury, astrocytes show detrimental effects against neurons. It is also known that astrocytes sometimes exert beneficial effects, such as neuroprotection and secretion of axonal growth factors. If beneficial effects of astrocytes after injury could be induced, dysfunction of the injured CNS may improve. However, a way of promoting beneficial functions in astrocytes has not been elucidated. In the current study, we focused on neuroleukin (NLK), which is known to have axonal growth activities in neurons. Although NLK is secreted from astrocytes, the function of NLK in astrocytes is poorly understood. We aimed to clarify the mechanism of NLK secretion in astrocytes and the functional significance of secreted NLK from astrocytes. Stimulation of cultured astrocytes with recombinant NLK significantly elevated the secretion of NLK from astrocytes. Furthermore, astrocyte conditioned medium treated with NLK increased axonal density in cultured cortical neurons. Recombinant NLK itself directly increased axonal density in cultured neurons. These results indicated that NLK secreted from astrocytes acted as an axonal growth factor and that secretion was stimulated by extracellular NLK. To elucidate a direct binding molecule of NLK on astrocytes, drug affinity responsive target stability (DARTS) analysis was performed. A 78 kDa glucose regulated protein (GRP78) was identified as a receptor for NLK, which was related to the secretion of NLK from astrocytes. When NLK was injected into the lesion site of spinal cord injured mice, axonal density in the injured region was significantly increased and hindlimb motor function improved. These results suggested that NLK-GRP78 signalling was important for the beneficial effects of astrocytes. This study strengthens the potential of astrocytes for use as therapeutic targets in CNS traumatic injury.

Matrine Directly Activates Extracellular Heat Shock Protein 90, Resulting in Axonal Growth and Functional Recovery in Spinal Cord Injured-Mice.

After spinal cord injury (SCI), reconstruction of neuronal tracts is very difficult because an inhibitory scar is formed at the lesion site, in which several axonal growth inhibitors, such as chondroitin sulfate proteoglycans (CSPG), accumulate. We previously found that matrine, a major alkaloid in Sophora flavescens, enhanced axonal growth in neurons seeded on CSPG coating. The aims of this study were to investigate therapeutic effects of matrine in SCI mice and to clarify the underlying mechanism. Matrine was orally administered to contusion SCI mice. In the matrine-treated mice, motor dysfunction of the hindlimbs was improved, and the density of 5-HT-positive tracts was increased in the injured spinal cord. We explored putative direct binding proteins of matrine in cultured neurons using drug affinity responsive target stability (DARTS). As a result, heat shock protein 90 (HSP90) was identified, and matrine enhanced HSP90 chaperon activity. We then presumed that extracellular HSP90 is a matrine-targeting signaling molecule, and found that specific blocking of extracellular HSP90 by a neutralizing antibody completely diminished matrine-induced axonal growth and SCI amelioration. Our results suggest that matrine enhances axonal growth and functional recovery in SCI mice by direct activation of extracellular HSP90. Matrine could be a significant candidate for therapeutic drugs for SCI with a novel mechanism.

Author Correction: HDAC3 inhibition ameliorates spinal cord injury by immunomodulation.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Polygalae Radix Extract Prevents Axonal Degeneration and Memory Deficits in a Transgenic Mouse Model of Alzheimer's Disease.

Memory impairments in Alzheimer's disease (AD) occur due to degenerated axons and disrupted neural networks. Since only limited recovery is possible after the destruction of neural networks, preventing axonal degeneration during the early stages of disease progression is necessary to prevent AD. Polygalae Radix (roots of Polygala tenuifolia; PR) is a traditional herbal medicine used for sedation and amnesia. In this study, we aimed to clarify and analyze the preventive effects of PR against memory deficits in a transgenic AD mouse model, 5XFAD. 5XFAD mice demonstrated memory deficits at the age of 5 months. Thus, the water extract of Polygalae Radix (PR extract) was orally administered to 4-month-old 5XFAD mice that did not show signs of memory impairment. After consecutive administrations for 56 days, the PR extract prevented cognitive deficit and axon degeneration associated with the accumulation of amyloid ß (Aß) plaques in the perirhinal cortex of the 5XFAD mice. PR extract did not influence the formation of Aß plaques in the brain of the 5XFAD mice. In cultured neurons, the PR extract prevented axonal growth cone collapse and axonal atrophy induced by Aß. Additionally, it prevented Aß-induced endocytosis at the growth cone of cultured neurons. Our previous study reported that endocytosis inhibition was enough to prevent Aß-induced growth cone collapse, axonal degeneration, and memory impairments. Therefore, the PR extract possibly prevented axonal degeneration and memory impairment by inhibiting endocytosis. PR is the first preventive drug candidate for AD that inhibits endocytosis in neurons.

HDAC3 inhibition ameliorates spinal cord injury by immunomodulation.

Following spinal cord injury (SCI), the innate immune response of microglia and infiltrating macrophages clears up cellular debris and promotes tissue repair, but it also inflicts secondary injury from inflammatory responses. Immunomodulation aimed at maximizing the beneficial effects while minimizing the detrimental roles of the innate immunity may aid functional recovery after SCI. However, intracellular drivers of global reprogramming of the inflammatory gene networks in the innate immune cells are poorly understood. Here we show that SCI resulted in an upregulation of histone deacetylase 3 (HDAC3) in the innate immune cells at the injury site. Remarkably, blocking HDAC3 with a selective small molecule inhibitor shifted microglia/macrophage responses towards inflammatory suppression, resulting in neuroprotective phenotypes and improved functional recovery in SCI model. Mechanistically, HDAC3 activity is largely responsible for histone deacetylation and inflammatory responses of primary microglia to classic inflammatory stimuli. Our results reveal a novel function of HDAC3 inhibitor in promoting functional recovery after SCI by dampening inflammatory cytokines, thus pointing towards a new direction of immunomodulation for SCI repair.

A Systematic Strategy for Discovering a Therapeutic Drug for Alzheimer's Disease and Its Target Molecule.

Natural medicines are attractive sources of leading compounds that can be used as interventions for neurodegenerative disorders. The complexity of their chemical components and undetermined bio-metabolism have greatly hindered both the use of natural medicines and the identification of their active constituents. Here, we report a systematic strategy for evaluating the bioactive candidates in natural medicines used for Alzheimer's disease (AD). We found that Drynaria Rhizome could enhance memory function and ameliorate AD pathologies in 5XFAD mice. Biochemical analysis led to the identification of the bio-effective metabolites that are transferred to the brain, namely, naringenin and its glucuronides. To explore the mechanism of action, we combined the drug affinity responsive target stability with immunoprecipitation-liquid chromatography/mass spectrometry analysis, identifying the collapsin response mediator protein 2 protein as a target of naringenin. Our study indicates that biochemical analysis coupled with pharmacological methods can be used in the search for new targets for AD intervention.

A Novel Rac1-GSPT1 Signaling Pathway Controls Astrogliosis Following Central Nervous System Injury.

Astrogliosis (i.e. glial scar), which is comprised primarily of proliferated astrocytes at the lesion site and migrated astrocytes from neighboring regions, is one of the key reactions in determining outcomes after CNS injury. In an effort to identify potential molecules/pathways that regulate astrogliosis, we sought to determine whether Rac/Rac-mediated signaling in astrocytes represents a novel candidate for therapeutic intervention following CNS injury. For these studies, we generated mice with Rac1 deletion under the control of the GFAP (glial fibrillary acidic protein) promoter (GFAP-Cre;Rac1flox/flox). GFAP-Cre;Rac1flox/flox (Rac1-KO) mice exhibited better recovery after spinal cord injury and exhibited reduced astrogliosis at the lesion site relative to control. Reduced astrogliosis was also observed in Rac1-KO mice following microbeam irradiation-induced injury. Moreover, knockdown (KD) or KO of Rac1 in astrocytes (LN229 cells, primary astrocytes, or primary astrocytes from Rac1-KO mice) led to delayed cell cycle progression and reduced cell migration. Rac1-KD or Rac1-KO astrocytes additionally had decreased levels of GSPT1 (G1 to S phase transition 1) expression and reduced responses of IL-1ß and GSPT1 to LPS treatment, indicating that IL-1ß and GSPT1 are downstream molecules of Rac1 associated with inflammatory condition. Furthermore, GSPT1-KD astrocytes had cell cycle delay, with no effect on cell migration. The cell cycle delay induced by Rac1-KD was rescued by overexpression of GSPT1. Based on these results, we propose that Rac1-GSPT1 represents a novel signaling axis in astrocytes that accelerates proliferation in response to inflammation, which is one important factor in the development of astrogliosis/glial scar following CNS injury.