Caloric restriction suppresses microglial activation and prevents neuroapoptosis following cortical injury in rats

Traumatic brain injury (TBI) is a widespread cause of death and a major source of adult disability. Subsequent pathological events occurring in the brain after TBI, referred to as secondary injury, continue to damage surrounding tissue resulting in substantial neuronal loss. One of the hallmarks of the secondary injury process is microglial activation resulting in increased cytokine production. Notwithstanding that recent studies demonstrated that caloric restriction (CR) lasting several months prior to an acute TBI exhibits neuroprotective properties, understanding how exactly CR influences secondary injury is still unclear. The goal of the present study was to examine whether CR (50% of daily food intake for 3 months) alleviates the effects of secondary injury on neuronal loss following cortical stab injury (CSI). To this end, we examined the effects of CR on the microglial activation, tumor necrosis factor-α (TNF-α) and caspase-3 expression in the ipsilateral (injured) cortex of the adult rats during the recovery period (from 2 to 28 days) after injury. Our results demonstrate that CR prior to CSI suppresses microglial activation, induction of TNF-α and caspase-3, as well as neurodegeneration following injury. These results indicate that CR strongly attenuates the effects of secondary injury, thus suggesting that CR may increase the successful outcome following TBI.     

Oxidative stress,DNA damage,and the telomeric complex as therapeutic targets in acute neurodegeneration

Oxidative stress has been identified as an important contributor to neurodegeneration associated with acute CNS injuries and diseases such as spinal cord injury (SCI), traumatic brain injury (TBI), and ischemic stroke. In this review, we briefly detail the damaging effects of oxidative stress (lipid peroxidation, protein oxidation, etc.) with a particular emphasis on DNA damage. Evidence for DNA damage in acute CNS injuries is presented along with its downstream effects on neuronal viability. In particular, unchecked oxidative DNA damage initiates a series of signaling events (e.g. activation of p53 and PARP-1, cell cycle re-activation) which have been shown to promote neuronal loss following CNS injury. These findings suggest that preventing DNA damage might be an effective way to promote neuronal survival and enhance neurological recovery in these conditions. Finally, we identify the telomere and telomere-associated proteins (e.g. telomerase) as novel therapeutic targets in the treatment of neurodegeneration due to their ability to modulate the neuronal response to both oxidative stress and DNA damage.     

Systemic inflammation modulates Fc receptor expression on microglia during chronic neurodegeneration

Chronic neurodegeneration is a major worldwide health problem, and it has been suggested that systemic inflammation can accelerate the onset and progression of clinical symptoms. A possible explanation is that systemic inflammation "switches" the phenotype of microglia from a relatively benign to a highly aggressive and tissue-damaging phenotype. The current study investigated the molecular mechanism underlying this microglia phenotype "switching." We show in mice with chronic neurodegeneration (ME7 prion model) that there is increased expression of receptors that have a key role in macrophage activation and associated signaling pathways, including TREM-2, Siglec-F, CD200R, and FcγRs. Systemic inflammation induced by LPS further increased protein levels of the activating FcγRIII and FcγRIV, but not of other microglial receptors, including the inhibitory FcγRII. In addition to these changes in receptor expression, IgG levels in the brain parenchyma were increased during chronic neurodegeneration, and these IgG levels further increased after systemic inflammation. γ-Chain-deficient mice show modified proinflammatory cytokine expression in the brain after systemic inflammation. We conclude that systemic inflammation during chronic neurodegeneration increases the expression levels of activating FcγR on microglia and thereby lowers the signaling threshold for Ab-mediated cell activation. At the same time, IgG influx into the brain could provide a cross-linking ligand resulting in excessive microglia activation that is detrimental to neurons already under threat by misfolded protein.     

Regulation of Microglial Phagocytosis by RhoA/ROCK-Inhibiting Drugs

Inflammation within the central nervous system (CNS) is a major component of many neurodegenerative diseases. The underlying mechanisms of neuronal loss are not fully understood, but the activation of CNS resident phagocytic microglia seems to be a significant element contributing to neurodegeneration. At the onset of inflammation, high levels of microglial phagocytosis may serve as an essential prerequisite for creating a favorable environment for neuronal regeneration. However, the excessive and long-lasting activation of microglia and the augmented engulfment of neurons have been suggested to eventually govern widespread neurodegeneration. Here, we investigated in a functional assay of acute inflammation how the small GTPase RhoA and its main target the Rho kinase (ROCK) influence microglial phagocytosis of neuronal debris. Using BV-2 microglia and human NT2 model neurons, we demonstrate that the pain reliever Ibuprofen decreases RhoA activation and microglial phagocytosis of neuronal cell fragments. Inhibition of the downstream effector ROCK with the small-molecule agents Y-27632 and Fasudil reduces the engulfment of neuronal debris and attenuates the production of the inflammatory mediator nitric oxide during stimulation with lipopolysaccharide. Our results support a therapeutic potential for RhoA/ROCK-inhibiting agents as an effective treatment of excessive inflammation and the resulting progression of microglia-mediated neurodegeneration in the CNS.     

In Vivo Dynamics of Retinal Microglial Activation During Neurodegeneration: Confocal Ophthalmoscopic Imaging and Cell Morphometry in Mouse Glaucoma

Microglia, which are CNS-resident neuroimmune cells, transform their morphology and size in response to CNS damage, switching to an activated state with distinct functions and gene expression profiles. The roles of microglial activation in health, injury and disease remain incompletely understood due to their dynamic and complex regulation in response to changes in their microenvironment. Thus, it is critical to non-invasively monitor and analyze changes in microglial activation over time in the intact organism. In vivo studies of microglial activation have been delayed by technical limitations to tracking microglial behavior without altering the CNS environment. This has been particularly challenging during chronic neurodegeneration, where long-term changes must be tracked. The retina, a CNS organ amenable to non-invasive live imaging, offers a powerful system to visualize and characterize the dynamics of microglia activation during chronic disorders.This protocol outlines methods for long-term, in vivo imaging of retinal microglia, using confocal ophthalmoscopy (cSLO) and CX3CR1^GFP/+ reporter mice, to visualize microglia with cellular resolution. Also, we describe methods to quantify monthly changes in cell activation and density in large cell subsets (200-300 cells per retina). We confirm the use of somal area as a useful metric for live tracking of microglial activation in the retina by applying automated threshold-based morphometric analysis of in vivo images. We use these live image acquisition and analyses strategies to monitor the dynamic changes in microglial activation and microgliosis during early stages of retinal neurodegeneration in a mouse model of chronic glaucoma. This approach should be useful to investigate the contributions of microglia to neuronal and axonal decline in chronic CNS disorders that affect the retina and optic nerve.     

Long-Term Upregulation of Inflammation and Suppression of Cell Proliferation in the Brain of Adult Rats Exposed to Traumatic Brain Injury Using the Controlled Cortical Impact Model

The long-term consequences of traumatic brain injury (TBI), specifically the detrimental effects of inflammation on the neurogenic niches, are not very well understood. In the present in vivo study, we examined the prolonged pathological outcomes of experimental TBI in different parts of the rat brain with special emphasis on inflammation and neurogenesis. Sixty days after moderate controlled cortical impact injury, adult Sprague-Dawley male rats were euthanized and brain tissues harvested. Antibodies against the activated microglial marker, OX6, the cell cycle-regulating protein marker, Ki67, and the immature neuronal marker, doublecortin, DCX, were used to estimate microglial activation, cell proliferation, and neuronal differentiation, respectively, in the subventricular zone (SVZ), subgranular zone (SGZ), striatum, thalamus, and cerebral peduncle. Stereology-based analyses revealed significant exacerbation of OX6-positive activated microglial cells in the striatum, thalamus, and cerebral peduncle. In parallel, significant decrements in Ki67-positive proliferating cells in SVZ and SGZ, but only trends of reduced DCX-positive immature neuronal cells in SVZ and SGZ were detected relative to sham control group. These results indicate a progressive deterioration of the TBI brain over time characterized by elevated inflammation and suppressed neurogenesis. Therapeutic intervention at the chronic stage of TBI may confer abrogation of these deleterious cell death processes.     

Tamoxifen attenuates inflammatory-mediated damage and improves functional outcome after spinal cord injury in rats

Tamoxifen has been found to be neuroprotective in both transient and permanent experimental ischemic stroke. However, it remains unknown whether this agent shows a similar beneficial effect after spinal cord injury (SCI), and what are its underlying mechanisms. In this study, we investigated the efficacy of tamoxifen treatment in attenuating SCI-induced pathology. Blood–spinal cord barrier (BSCB) permeability, tissue edema formation, microglial activation, neuronal cell death and myelin loss were determined in rats subjected to spinal cord contusion. The results showed that tamoxifen, administered at 30 min post-injury, significantly decreased interleukin-1β (IL-1β) production induced by microglial activation, alleviated the amount of Evans blue leakage and edema formation. In addition, tamoxifen treatment clearly reduced the number of apoptotic neurons post-SCI. The myelin loss and the increase in production of myelin-associated axonal growth inhibitors were also found to be significantly attenuated at day 3 post-injury. Furthermore, rats treated with tamoxifen scored much higher on the locomotor rating scale after SCI than did vehicle-treated rats, suggesting improved functional outcome after SCI. Together, these results demonstrate that tamoxifen provides neuroprotective effects for treatment of SCI-related pathology and disability, and is therefore a potential neuroprotectant for human spinal cord injury therapy.     

Peripheral inflammatory mechanisms modulate microglial activation in response to mild impairment of oxidative metabolism

Thiamine deficiency (TD) models the selective neurodegeneration that accompanies the mild impairment of oxidative metabolism, which is observed in a variety of neurodegenerative diseases. Several markers of inflammation accompany neuronal death in TD and in these diseases. Studies in the submedial thalamic nucleus (SmTN), the region most sensitive to TD, have begun to define the temporal response of inflammation, immune response and neurodegeneration. Our previous studies show that the immune response is involved in TD-induced neurodegeneration. The current experiments tested the roles of other inflammatory cascades in TD-induced neuronal death. Deletion of genes for CD4, or CD8 (the co-receptors for T-cells), IFN-gamma (the cytokine produced by T-cell), or NADPH oxidase (the inflammation related oxidase) were tested. None protected against neuronal death in late stages of TD. On the other hand, deletion of the genes for CD4, CD8 and IFN-gamma increased the microglial activation, and deletion of the gene for NADPH oxidase decreased microglial activation when compared to control mice. In wild type mice, TD caused hypertrophy of CD68 positive microglia without increasing the number of microglia. However, TD induced hypertrophy and proliferation of CD68-positive microglia in the CD4 (97%), CD8 (57%) or IFN-gamma (96%) genetic knockout mice. In the genetic knockout mice for NADPH oxidase, the microglial activation was 65% less than the wild type mice. The results demonstrate that mice deficient in specific T cells (CD4-/-, CD8-/-) or activated T cell product, (IFN-gamma-/-) have increased microglia activation, but mice deficient in NADPH oxidase have decreased microglial activation. However, at the time point tested, the deletions were not neuroprotective. The results suggest that inflammatory responses play a role in TD-induced pathological changes in the brain, and the inflammation appears to be a late event that reflects a response to neuronal damage, which may spread the damage to other brain regions.     

Microglial activation and recruitment,but not proliferation,suffice to mediate neurodegeneration

Microglial activation occurs during excitotoxin-induced neurodegeneration. We have reported that microglia can exhibit neurotoxic behaviors after injection of excitotoxins into the hippocampus. It is not known, however, whether microglial proliferation, which is part of the activation response, is required for neurodegeneration to be observed, or whether activation of the pre-existing resident microglia suffices. Using osteopetrotic (op/op) mice, in which injury-induced microglial proliferation does not take place, we demonstrate that only the microglia initially residing in the CNS are adequate to promote neurodegeneration. Our data suggest that there is a threshold at which a maximal microglial contribution to neurotoxicity is observed. This threshold appears to be sufficiently low, such that activation of just 40% of the microglia present in wild-type mice serves to trigger neurodegeneration. Furthermore, since the decrease in microglial numbers coincides with a decrease in tissue plasminogen activator's activity, we suggest that tissue plasminogen activator can be used as a marker for microglial proliferation.     

Microglial AGE-Albumin Is Critical in Promoting Alcohol-Induced Neurodegeneration in Rats and Humans

Alcohol is a neurotoxic agent, since long-term heavy ingestion of alcohol can cause various neural diseases including fetal alcohol syndrome, cerebellar degeneracy and alcoholic dementia. However, the molecular mechanisms of alcohol-induced neurotoxicity are still poorly understood despite numerous studies. Thus, we hypothesized that activated microglial cells with elevated AGE-albumin levels play an important role in promoting alcohol-induced neurodegeneration. Our results revealed that microglial activation and neuronal damage were found in the hippocampus and entorhinal cortex following alcohol treatment in a rat model. Increased AGE-albumin synthesis and secretion were also observed in activated microglial cells after alcohol exposure. The expressed levels of receptor for AGE (RAGE)-positive neurons and RAGE-dependent neuronal death were markedly elevated by AGE-albumin through the mitogen activated protein kinase pathway. Treatment with soluble RAGE or AGE inhibitors significantly diminished neuronal damage in the animal model. Furthermore, the levels of activated microglial cells, AGE-albumin and neuronal loss were significantly elevated in human brains from alcoholic indivisuals compared to normal controls. Taken together, our data suggest that increased AGE-albumin from activated microglial cells induces neuronal death, and that efficient regulation of its synthesis and secretion is a therapeutic target for preventing alcohol-induced neurodegeneration.     

Microglial LOX-1 reacts with extracellular HSP60 to bridge neuroinflammation and neurotoxicity

Chronic neurodegeneration is in part caused by a vicious cycle of persistent microglial activation and progressive neuronal cell loss. However, the driving force behind this cycle remains poorly understood. In this study, we used medium conditioned by necrotic differentiated-PC12 cells to confirm that damaged neurons can release soluble injury signals, including heat shock protein 60 (HSP60), to efficiently promote the neurotoxic cycle involving microglia. Since lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) has previously been identified as a novel receptor for HSP60, we hypothesize that LOX-1 through binding to extracellular HSP60 promotes microglia-mediated neuroinflammation. In this study, we observed that LOX-1 expression is induced upon toxic microglial activation, and discovered that LOX-1 is necessary in microglia for sensing soluble neuronal injury signal(s) in the conditioned medium to induce generation of pro-inflammatory mediators (IL-1β, TNF-α, NO and ROS) that promote neurotoxicity. Employing a unique eukaryotic HSP60-overexpression method, we further demonstrated that extracellular HSP60 acts on microglial LOX-1 to boost the production of pro-inflammatory factors (IL-1β, NO and ROS) in microglia and to propagate neuronal damage. These results indicate that LOX-1 is essential in microglia for promoting an inflammatory response in the presence of soluble neuronal-injury signals such as extracellular HSP60, thereby linking neuroinflammation and neurotoxicity.     

Altered Spontaneous Brain Activity in Patients with Acute Spinal Cord Injury Revealed by Resting-State Functional MRI

Background

Previous neuroimaging studies have provided evidence of structural and functional reorganization of brain in patients with chronic spinal cord injury (SCI). However, it remains unknown whether the spontaneous brain activity changes in acute SCI. In this study, we investigated intrinsic brain activity in acute SCI patients using a regional homogeneity (ReHo) analysis based on resting-state functional magnetic resonance imaging.

Methods

A total of 15 patients with acute SCI and 16 healthy controls participated in the study. The ReHo value was used to evaluate spontaneous brain activity, and voxel-wise comparisons of ReHo were performed to identify brain regions with altered spontaneous brain activity between groups. We also assessed the associations between ReHo and the clinical scores in brain regions showing changed spontaneous brain activity.

Results

Compared with the controls, the acute SCI patients showed decreased ReHo in the bilateral primary motor cortex/primary somatosensory cortex, bilateral supplementary motor area/dorsal lateral prefrontal cortex, right inferior frontal gyrus, bilateral dorsal anterior cingulate cortex and bilateral caudate; and increased ReHo in bilateral precuneus, the left inferior parietal lobe, the left brainstem/hippocampus, the left cingulate motor area, bilateral insula, bilateral thalamus and bilateral cerebellum. The average ReHo values of the left thalamus and right insula were negatively correlated with the international standards for the neurological classification of spinal cord injury motor scores.

Conclusion

Our findings indicate that acute distant neuronal damage has an immediate impact on spontaneous brain activity. In acute SCI patients, the ReHo was prominently altered in brain regions involved in motor execution and cognitive control, default mode network, and which are associated with sensorimotor compensatory reorganization. Abnormal ReHo values in the left thalamus and right insula could serve as potential biomarkers for assessment of neuronal damage and the prediction of clinical outcomes in acute SCI.     

Role of the Cell Cycle in the Pathobiology of Central Nervous System Trauma

Up-regulation of cell cycle proteins occurs in both mitotic and post-mitotic neural cells after central nervous system (CNS) injury in adult animals. In mitotic cells, such as astroglia and microglia, they induce proliferation, whereas in post-mitotic cells such as neurons they initiate caspase-related apoptosis. We recently reported that early central administration of the cell cycle inhibitor flavopiridol after experimental traumatic brain injury (TBI) significantly reduced lesion volume, scar formation and neuronal cell death, while promoting near complete behavioral recovery. Here we show that in primary neuronal or astrocyte cultures structurally different cell cycle inhibitors (flavopiridol, roscovitine, and olomoucine) significantly reduce up-regulation of cell cycle proteins, attenuate neuronal cell death induced by etoposide, and decrease astrocyte proliferation. Flavopiridol, in a concentration dependent manner, also attenuates proliferation/activation of microglia. In addition, we demonstrate that central administration of flavopiridol improves functional outcome in dose-dependent manner after fluid percussion induced brain injury in rats. Moreover, delayed systemic administration of flavopiridol significantly reduces brain lesion volume and edema development after TBI. These data provide further support for the therapeutic potential of cell cycle inhibitors for the treatment of clinical CNS injury and that protective mechanisms likely include reduction of neuronal cell death, inhibition of glial proliferation and attenuation of microglial activation.     

Microglia-Specific Metabolic Changes in Neurodegeneration

The high energetic demand of the brain deems this organ rather sensitive to changes in energy supply. Therefore, even minor alterations in energy metabolism may underlie detrimental disturbances in brain function, contributing to the generation and progression of neurodegenerative diseases. Considerable evidence supports the key role of deficits in cerebral energy metabolism, particularly hypometabolism of glucose and mitochondrial dysfunction, in the pathophysiology of brain disorders. Major breakthroughs in the field of bioenergetics and neurodegeneration have been achieved through the use of in vitro and in vivo models of disease as well as sophisticated neuroimaging techniques in patients, yet these have been mainly focused on neuron and astrocyte function. Remarkably, the subcellular metabolic mechanisms linked to neurodegeneration that operate in other crucial brain cell types such as microglia have remain obscured, although they are beginning to be unraveled. Microglia, the brain-resident immune sentinels, perform a diverse range of functions that require a high-energy expenditure, namely, their role in brain development, maintenance of the neural environment, response to injury and infection, and activation of repair programs. Interestingly, another key mechanism underlying several neurodegenerative diseases is neuroinflammation, which can be associated with chronic microglia activation. Considering that many brain disorders are accompanied by changes in brain energy metabolism and sustained inflammation, and that energy metabolism has a strong influence on the inflammatory responses of microglia, the emerging significance of microglial energy metabolism in neurodegeneration is highlighted in this review.     

Neuroprotective effect of Scutellaria baicalensis on spinal cord injury in rats

Inflammation has been known to play an important role in the pathogenesis after spinal cord injury (SCI). Microglia are activated after injury and produce a variety of proinflammatory factors such as tumor necrosis factor-α, interleukin-1β, cyclooxygenase-2, and reactive oxygen species leading to apoptosis of neurons and oligodendrocytes. In this study, we examined the neuroprotective effects of total ethanol extract of Scutellaria baicalensis (EESB) , after SCI. Using primary microglial cultures, EESB treatment significantly inhibited lipopolysaccharide-induced expression of such inflammatory mediators as tumor necrosis factor-α, IL-1β, IL-6, cyclooxygenase-2, and inducible nitric oxide synthase. Furthermore, reactive oxygen species and nitric oxide production were significantly attenuated by EESB treatment. For in vivo study, rats that had received a moderate spinal cord contusion injury at T9 received EESB orally at a dose of 100 mg/kg. EESB inhibited expression of proinflammatory factors and protein carbonylation and nitration after SCI. EESB also inhibited microglial activation at 4 h after injury. Furthermore, EESB significantly inhibited apoptotic cell death of neurons and oligodendrocytes and improved functional recovery after SCI. Lesion cavity and myelin loss were also reduced following EESB treatment. Thus, our data suggest that EESB significantly improve functional recovery by inhibiting inflammation and oxidative stress after injury.     

Involvement of dopaminergic neuronal cystatin C in neuronal injury-induced microglial activation and neurotoxicity

Factors released from injured dopaminergic (DA) neurons may trigger microglial activation and set in motion a vicious cycle of neuronal injury and inflammation that fuels progressive DA neurodegeneration in Parkinson's disease. In this study, using proteomic and immunoblotting analysis, we detected elevated levels of cystatin C in conditioned media (CM) from 1-methyl-4-phenylpyridinium and dieldrin-injured rat DA neuronal cells. Immunodepletion of cystatin C significantly reduced the ability of DA neuronal CM to induce activation of rat microglial cells as determined by up-regulation of inducible nitric oxide synthase, production of free radicals and release of proinflammatory cytokines as well as activated microglia-mediated DA neurotoxicity. Treatment of the cystatin C-containing CM with enzymes that remove O- and sialic acid-, but not N-linked carbohydrate moieties markedly reduced the ability of the DA neuronal CM to activate microglia. Taken together, these results suggest that DA neuronal cystatin C plays a role in the neuronal injury-induced microglial activation and neurotoxicity. These findings from the rat DA neuron-microglia in vitro model may help guide continued investigation to define the precise role of cystatin C in the complex interplay among neurons and glia in the pathogenesis of Parkinson's disease.     

Delayed cell cycle pathway modulation facilitates recovery after spinal cord injury

Traumatic spinal cord injury (SCI) causes tissue loss and associated neurological dysfunction through mechanical damage and secondary biochemical and physiological responses. We have previously described the pathobiological role of cell cycle pathways following rat contusion SCI by examining the effects of early intrathecal cell cycle inhibitor treatment initiation or gene knockout on secondary injury. Here, we delineate changes in cell cycle pathway activation following SCI and examine the effects of delayed (24 h) systemic administration of flavopiridol, an inhibitor of major cyclin-dependent kinases (CDKs), on functional recovery and histopathology in a rat SCI contusion model. Immunoblot analysis demonstrated a marked upregulation of cell cycle-related proteins, including pRb, cyclin D1, CDK4, E2F1 and PCNA, at various time points following SCI, along with downregulation of the endogenous CDK inhibitor p27. Treatment with flavopiridol reduced induction of cell cycle proteins and increased p27 expression in the injured spinal cord. Functional recovery was significantly improved after SCI from day 7 through day 28. Treatment significantly reduced lesion volume and the number of Iba-1⁺ microglia in the preserved tissue and increased the myelinated area of spared white matter as well as the number of CC1⁺ oligodendrocytes. Furthermore, flavopiridol attenuated expression of Iba-1 and glactin-3, associated with microglial activation and astrocytic reactivity by reduction of GFAP, NG2, and CHL1 expression. Our current study supports the role of cell cycle activation in the pathophysiology of SCI and by using a clinically relevant treatment model, provides further support for the therapeutic potential of cell cycle inhibitors in the treatment of human SCI.     

Delayed cell cycle pathway modulation facilitates recovery after spinal cord injury

Traumatic spinal cord injury (SCI) causes tissue loss and associated neurological dysfunction through mechanical damage and secondary biochemical and physiological responses. We have previously described the pathobiological role of cell cycle pathways following rat contusion SCI by examining the effects of early intrathecal cell cycle inhibitor treatment initiation or gene knockout on secondary injury. Here, we delineate changes in cell cycle pathway activation following SCI and examine the effects of delayed (24 h) systemic administration of flavopiridol, an inhibitor of major cyclin-dependent kinases (CDKs), on functional recovery and histopathology in a rat SCI contusion model. Immunoblot analysis demonstrated a marked upregulation of cell cycle-related proteins, including pRb, cyclin D1, CDK4, E2F1 and PCNA, at various time points following SCI, along with downregulation of the endogenous CDK inhibitor p27. Treatment with flavopiridol reduced induction of cell cycle proteins and increased p27 expression in the injured spinal cord. Functional recovery was significantly improved after SCI from day 7 through day 28. Treatment significantly reduced lesion volume and the number of Iba-1⁺ microglia in the preserved tissue and increased the myelinated area of spared white matter as well as the number of CC1⁺ oligodendrocytes. Furthermore, flavopiridol attenuated expression of Iba-1 and glactin-3, associated with microglial activation and astrocytic reactivity by reduction of GFAP, NG2, and CHL1 expression. Our current study supports the role of cell cycle activation in the pathophysiology of SCI and by using a clinically relevant treatment model, provides further support for the therapeutic potential of cell cycle inhibitors in the treatment of human SCI.     

Dual regulation of microglia and neurons by Astragaloside IV‐mediated mTORC1 suppression promotes functional recovery after acute spinal cord injury

Inflammation and neuronal apoptosis contribute to the progression of secondary injury after spinal cord injury (SCI) and are targets for SCI therapy; autophagy is reported to suppress apoptosis in neuronal cells and M2 polarization may attenuate inflammatory response in microglia, while both are negatively regulated by mTORC1 signalling. We hypothesize that mTORC1 suppression may have dual effects on inflammation and neuronal apoptosis and may be a feasible approach for SCI therapy. In this study, we evaluate a novel inhibitor of mTORC1 signalling, Astragaloside IV (AS‐IV), in vitro and in vivo. Our results showed that AS‐IV may suppress mTORC1 signalling both in neuronal cells and microglial cells in vitro and in vivo. AS‐IV treatment may stimulate autophagy in neuronal cells and protect them against apoptosis through autophagy regulation; it may also promote M2 polarization in microglial cells and attenuate neuroinflammation. In vivo, rats were intraperitoneally injected with AS‐IV (10 mg/kg/d) after SCI, behavioural and histological evaluations showed that AS‐IV may promote functional recovery in rats after SCI. We propose that mTORC1 suppression may attenuate both microglial inflammatory response and neuronal apoptosis and promote functional recovery after SCI, while AS‐IV may become a novel therapeutic medicine for SCI.