The role of autophagy in modulation of neuroinflammation in microglia

MicroRNAs Dysregulation and Metabolism in Multiple System Atrophy

Multiple system atrophy (MSA) is an adult onset, fatal disease, characterized by an accumulation of alpha-synuclein (α-syn) in oligodendroglial cells. MicroRNAs (miRNAs) are small non-coding RNAs involved in post-translational regulation and several biological processes. Disruption of miRNA-related pathways in the central nervous system (CNS) plays an important role in the pathogenesis of neurodegenerative diseases, including MSA. While the exact mechanisms underlying miRNAs in the pathogenesis of MSA remain unclear, it is known that miRNAs can repress the translation of messenger RNAs (mRNAs) that regulate the following pathogenesis associated with MSA: autophagy, neuroinflammation, α-syn accumulation, synaptic transmission, oxidative stress, and apoptosis. In this review, the metabolism of miRNAs and their functional roles in the pathogenesis of MSA are discussed, thereby highlighting miRNAs as potential new biomarkers for the diagnosis of MSA and in increasing our understanding of the disease process.

Interleukin-4 affects microglial autophagic flux

Interleukin-4 plays an important protective role in Alzheimer's disease by regulating microglial phenotype, phagocytosis of amyloid-β, and secretion of anti-inflammatory and neurotrophic cytokines. Recently, increasing evidence has suggested that autophagy regulates innate immunity by affecting M1/M2 polarization of microglia/macrophages. However, the role of interleukin-4 in microglial autophagy is unknown. In view of this, BV2 microglia were treated with 0, 10, 20 or 50 ng/mL interleukin-4 for 24, 48, or 72 hours. Subsequently, light chain 3-II and p62 protein expression levels were detected by western blot assay. BV2 microglia were incubated with interleukin-4 (20 ng/mL, experimental group), 3-methyladenine (500 μM, autophagy inhibitor, negative control group), rapamycin (100 nM, autophagy inductor, positive control group), 3-methyladenine + interleukin-4 (rescue group), or without treatment for 24 hours, and then exposed to amyloid-β (1 μM, model group) or vehicle control (control) for 24 hours. LC3-II and p62 protein expression levels were again detected by western blot assay. In addition, expression levels of multiple markers of M1 and M2 phenotype were assessed by real-time fluorescence quantitative polymerase chain reaction, while intracellular and supernatant amyloid-β protein levels were measured by enzyme-linked immunosorbent assay. Our results showed that interleukin-4 induced microglial autophagic flux, most significantly at 20 ng/mL for 48 hours. Interleukin-4 pretreated microglia inhibited blockade of amyloid-β-induced autophagic flux, and promoted amyloid-β uptake and degradation partly through autophagic flux, but inhibited switching of amyloid-β-induced M1 phenotype independent on autophagic flux. These results indicate that interleukin-4 pretreated microglia increases uptake and degradation of amyloid-β in a process partly mediated by autophagy, which may play a protective role against Alzheimer's disease.

Autophagy in Neurotrauma: Good, Bad, or Dysregulated

Autophagy is a physiological process that helps maintain a balance between the manufacture of cellular components and breakdown of damaged organelles and other toxic cellular constituents. Changes in autophagic markers are readily detectable in the spinal cord and brain following neurotrauma, including traumatic spinal cord and brain injury (SCI/TBI). However, the role of autophagy in neurotrauma remains less clear. Whether autophagy is good or bad is under debate, with strong support for both a beneficial and detrimental role for autophagy in experimental models of neurotrauma. Emerging data suggest that autophagic flux, a measure of autophagic degradation activity, is impaired in injured central nervous systems (CNS), and interventions that stimulate autophagic flux may provide neuroprotection in SCI/TBI models. Recent data demonstrating that neurotrauma can cause lysosomal membrane damage resulting in pathological autophagosome accumulation in the spinal cord and brain further supports the idea that the impairment of the autophagy-lysosome pathway may be a part of secondary injury processes of SCI/TBI. Here, we review experimental work on the complex and varied responses of autophagy in terms of both the beneficial and detrimental effects in SCI and TBI models. We also discuss the existing and developing therapeutic options aimed at reducing the disruption of autophagy to protect the CNS after injuries.

Long-Time Instead of Short-Time Exposure in Vitro and Administration in Vivo of Ochratoxin A Is Consistent in Immunosuppression

Ochratoxin A (OTA) is a mycotoxin produced by Aspergillus and Penicillium, contaminating in a wide variety of foods and feeds. Mycotoxins, including OTA, could cause immunosuppression in almost all previous studies in vivo. However, the vast majority of results in vitro showed that mycotoxins caused immunostimulation. Why the results of studies in vitro are contrary to studies in vivo is unknown. Our study aims to explore the underlying reason and mechanism of the paradoxical effect. In this study, porcine alveolar macrophage cell line 3D4/21 was chosen as an in vitro model and treated with 1.0 μg/mL OTA for different times. Some indexes, such as expression of inflammatory cytokines, migration, phagocytosis, macrophage polarization, autophagy-related proteins, and Akt1 phosphorylation, were detected. The results showed that pro-inflammatory cytokine expression, migration, and phagocytosis were increased, with macrophage polarization to the M1 phenotype at 24 h of OTA exposure. Surprisedly, anti-inflammatory cytokine expression was increased, cell phagocytosis and migration were decreased, and macrophage polarization was switched from M1 to M2 at 72 h of OTA exposure. Furthermore, we found that long-time exposure of OTA also suppressed autophagy, and the autophagy activator blocked the OTA-induced immunosuppression. Phosphorylation of Akt1 plays a positive role in autophagy inhibition. In conclusion, long-time instead of short-time exposure of OTA in vitro induced immunosuppression. The immunosuppression mechanism of OTA in vitro involved inhibition of autophagy through upregulating p-Akt1. Our results provide new insight into research on the mechanism of mycotoxin-induced immunosuppression in vitro.

Cell Clearing Systems Bridging Neuro-Immunity and Synaptic Plasticity

In recent years, functional interconnections emerged between synaptic transmission, inflammatory/immune mediators, and central nervous system (CNS) (patho)-physiology. Such interconnections rose up to a level that involves synaptic plasticity, both concerning its molecular mechanisms and the clinical outcomes related to its behavioral abnormalities. Within this context, synaptic plasticity, apart from being modulated by classic CNS molecules, is strongly affected by the immune system, and vice versa. This is not surprising, given the common molecular pathways that operate at the cross-road between the CNS and immune system. When searching for a common pathway bridging neuro-immune and synaptic dysregulations, the two major cell-clearing cell clearing systems, namely the ubiquitin proteasome system (UPS) and autophagy, take center stage. In fact, just like is happening for the turnover of key proteins involved in neurotransmitter release, antigen processing within both peripheral and CNS-resident antigen presenting cells is carried out by UPS and autophagy. Recent evidence unravelling the functional cross-talk between the cell-clearing pathways challenged the traditional concept of autophagy and UPS as independent systems. In fact, autophagy and UPS are simultaneously affected in a variety of CNS disorders where synaptic and inflammatory/immune alterations concur. In this review, we discuss the role of autophagy and UPS in bridging synaptic plasticity with neuro-immunity, while posing a special emphasis on their interactions, which may be key to defining the role of immunity in synaptic plasticity in health and disease.

Implications of Microglia in Amyotrophic Lateral Sclerosis and Frontotemporal Dementia

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are neurodegenerative disorders with clear similarities regarding their clinical, genetic and pathological features. Both are progressive, lethal disorders, with no current curative treatment available. Several genes that correlated with ALS and FTD are implicated in the same molecular pathways. Strikingly, many of these genes are not exclusively expressed in neurons, but also in glial cells, suggesting a multicellular pathogenesis. Moreover, chronic inflammation is a common feature observed in ALS and FTD, indicating an essential role of microglia, the resident immune cells of the central nervous system, in disease development and progression. In this review, we will provide a comprehensive overview of the implications of microglia in ALS and FTD. Specifically, we will focus on the role of impaired phagocytosis and increased inflammatory responses and their impact on microglial function. Several genes associated with the disorders can directly be linked to microglial activation, phagocytosis and neuroinflammation. Other genes associated with the disorders are implicated in biological pathways involved in protein degradation and autophagy. In general such mutations have been shown to cause abnormal protein accumulation and impaired autophagy. These impairments have previously been linked to affect the innate immune system in the central nervous system through inappropriate activation of microglia and neuroinflammation, highlighted in this review. Although it has been well established that microglia play essential roles in neurodegenerative disorders, the precise underlying mechanisms remain to be elucidated.

Neuronal autophagy aggravates microglial inflammatory injury by downregulating CX3CL1/fractalkine after ischemic stroke

Ischemic stroke often induces excessive neuronal autophagy, resulting in brain damage; meanwhile, inflammatory responses stimulated by ischemia exacerbate neural injury. However, interactions between neuronal autophagy and microglial inflammation following ischemic stroke are poorly understood. CX3CL1/fractalkine, a membrane-bound chemokine expressed on neurons, can suppress microglial inflammation by binding to its receptor CX3CR1 on microglia. In the present study, to investigate whether autophagy could alter CX3CL1 expression on neurons and consequently change microglial inflammatory activity, middle cerebral artery occlusion (MCAO) was established in Sprague-Dawley rats to model ischemic stroke, and tissues from the ischemic penumbra were obtained to evaluate autophagy level and microglial inflammatory activity. MCAO rats were administered 3-methyladenine (autophagy inhibitor) or Tat-Beclin 1 (autophagy inducer). Western blot assays were conducted to quantify expression of Beclin-1, nuclear factor kappa B p65 (NF-κB), light chain 3B (LC3B), and CX3CL1 in ischemic penumbra. Moreover, immunofluorescence staining was performed to quantify numbers of LC3B-, CX3CL1-, and Iba-1-positive cells in ischemic penumbra. In addition, enzyme linked immunosorbent assays were utilized to analyze concentrations of tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), interleukin 1 beta (IL-1β), and prostaglandin E2 (PGE2). A dry/wet weight method was used to detect brain water content, while 2,3,5,-triphenyltetrazolium chloride staining was utilized to measure infarct volume. The results demonstrated that autophagy signaling (Beclin-1 and LC3B expression) in penumbra was prominently activated by MCAO, while CX3CL1 expression on autophagic neurons was significantly reduced and microglial inflammation was markedly activated. However, after inhibition of autophagy signaling with 3-methyladenine, CX3CL1 expression on neurons was obviously increased, whereas Iba-1 and NF-κB expression was downregulated; TNF-α, IL-6, IL-1β, and PGE2 levels were decreased; and cerebral edema was obviously mitigated. In contrast, after treatment with the autophagy inducer Tat-Beclin 1, CX3CL1 expression on neurons was further reduced; Iba-1 and NF-κB expression was increased; TNF-α, IL-6, IL-1β, and PGE2 levels were enhanced; and cerebral edema was aggravated. Our study suggests that ischemia-induced neuronal autophagy facilitates microglial inflammatory injury after ischemic stroke, and the efficacy of this process may be associated with downregulated CX3CL1 expression on autophagic neurons.

TLR4 (toll-like receptor 4) activation suppresses autophagy through inhibition of FOXO3 and impairs phagocytic capacity of microglia

Macroautophagy/autophagy is a lysosome-dependent catabolic process for the turnover of proteins and organelles in eukaryotes. Autophagy plays an important role in immunity and inflammation, as well as metabolism and cell survival. Diverse immune and inflammatory signals induce autophagy in macrophages through pattern recognition receptors, such as toll-like receptors (TLRs). However, the physiological role of autophagy and its signaling mechanisms in microglia remain poorly understood. Microglia are phagocytic immune cells that are resident in the central nervous system and share many characteristics with macrophages. Here, we show that autophagic flux and expression of autophagy-related (Atg) genes in microglia are significantly suppressed upon TLR4 activation by lipopolysaccharide (LPS), in contrast to their stimulation by LPS in macrophages. Metabolomics analysis of the levels of phosphatidylinositol (PtdIns) and its 3-phosphorylated form, PtdIns3P, in combination with bioinformatics prediction, revealed an LPS-induced reduction in the synthesis of PtdIns and PtdIns3P in microglia but not macrophages. Interestingly, inhibition of PI3K, but not MTOR or MAPK1/3, restored autophagic flux with concomitant dephosphorylation and nuclear translocation of FOXO3. A constitutively active form of FOXO3 also induced autophagy, suggesting FOXO3 as a downstream target of the PI3K pathway for autophagy inhibition. LPS treatment impaired phagocytic capacity of microglia, including MAP1LC3B/LC3-associated phagocytosis (LAP) and amyloid β (Aβ) clearance. PI3K inhibition restored LAP and degradation capacity of microglia against Aβ. These findings suggest a unique mechanism for the regulation of microglial autophagy and point to the PI3K-FOXO3 pathway as a potential therapeutic target to regulate microglial function in brain disorders. Abbreviations: Atg: autophagy-related gene; Aβ: amyloid-β; BafA1: bafilomycin A₁; BECN1: beclin 1, autophagy related; BMDM: bone marrow-derived macrophage; CA: constitutively active; CNS: central nervous system; ZFYVE1/DFCP1: zinc finger, FYVE domain containing 1; FOXO: forkhead box O; ELISA:enzyme-linked immunosorbent assay; HBSS: Hanks balanced salt solution; LAP: LC3-associated phagocytosis; MAP1LC3B: microtubule-associated protein 1 light chain 3; LPS: lipopolysaccharide; LY: LY294002; MTOR: mechanistic target of rapamycin kinase; Pam₃CSK₄: N-palmitoyl-S-dipalmitoylglyceryl Cys-Ser-(Lys)₄; PtdIns: phosphatidylinositol; PtdIns3P: phosphatidylinositol-3-phosphate; PLA: proximity ligation assay; Poly(I:C): polyinosinic-polycytidylic acid; qRT-PCR: quantitative real-time polymerase chain reaction; RPS6KB1: ribosomal protein S6 kinase, polypeptide 1; TLR: Toll-like receptor; TNF: tumor necrosis factor; TFEB: transcription factor EB; TSPO: translocator protein.

From Systemic Inflammation to Neuroinflammation: The Case of Neurolupus

It took decades to arrive at the general consensus dismissing the notion that the immune system is independent of the central nervous system. In the case of uncontrolled systemic inflammation, the relationship between the two systems is thrown off balance and results in cognitive and emotional impairment. It is specifically true for autoimmune pathologies where the central nervous system is affected as a result of systemic inflammation. Along with boosting circulating cytokine levels, systemic inflammation can lead to aberrant brain-resident immune cell activation, leakage of the blood⁻brain barrier, and the production of circulating antibodies that cross-react with brain antigens. One of the most disabling autoimmune pathologies known to have an effect on the central nervous system secondary to the systemic disease is systemic lupus erythematosus. Its neuropsychiatric expression has been extensively studied in lupus-like disease murine models that develop an autoimmunity-associated behavioral syndrome. These models are very useful for studying how the peripheral immune system and systemic inflammation can influence brain functions. In this review, we summarize the experimental data reported on murine models developing autoimmune diseases and systemic inflammation, and we explore the underlying mechanisms explaining how systemic inflammation can result in behavioral deficits, with a special focus on in vivo neuroimaging techniques.

Microglial overexpression of fALS-linked mutant SOD1 induces SOD1 processing impairment, activation and neurotoxicity and is counteracted by the autophagy inducer trehalose

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disease. Mutations in the gene encoding copper/zinc superoxide dismutase-1 (SOD1) are responsible for most familiar cases, but the role of mutant SOD1 protein dysfunction in non-cell autonomous neurodegeneration, especially in relation to microglial activation, is still unclear. Here, we focused our study on microglial cells, which release SOD1 also through exosomes. We observed that in rat primary microglia the overexpression of the most-common SOD1 mutations linked to fALS (G93A and A4V) leads to SOD1 intracellular accumulation, which correlates to autophagy dysfunction and microglial activation. In primary contact co-cultures, fALS mutant SOD1 overexpression by microglial cells appears to be neurotoxic by itself. Treatment with the autophagy-inducer trehalose reduced mutant SOD1 accumulation in microglial cells, decreased microglial activation and abrogated neurotoxicity in the co-culture model. These data suggest that i) the alteration of the autophagic pathway due to mutant SOD1 overexpression is involved in microglial activation and neurotoxicity; ii) the induction of autophagy with trehalose reduces microglial SOD1 accumulation through proteasome degradation and activation, leading to neuroprotection. Our results provide a novel contribution towards better understanding key cellular mechanisms in non-cell autonomous ALS neurodegeneration.

Resveratrol alleviates ethanol-induced neuroinflammation in vivo and in vitro: Involvement of TLR2-MyD88-NF-κB pathway

Excessive ethanol (EtOH) intake affects cognitive function and leads to permanent learning and memory deficits. EtOH-induced neuroinflammation plays an important role in EtOH neurotoxicity. Studies have shown that EtOH activates microglia and induces an inflammatory response. Resveratrol (Rsv) is a natural polyphenol found in a wide variety of plants and fruits, and produces the neuroprotective and anti-inflammatory effects in the central nervous system. However, effect of Rsv on EtOH-induced neuroinflammation is still unknown. We investigated the anti-inflammatory effect of Rsv in the context of EtOH-induced neurotoxicity and the molecular mechanisms potentially involved in the effect. The results showed that treatment of rats with Rsv prevented the deficits of spatial reference memory induced by EtOH and mitigated EtOH-induced neuroinflammation by inhibiting microglial activation and decreasing the levels of inflammatory cytokines including interleukin-1β, interleukin-6 and tumor necrosis factor α. The further studies indicated that Rsv reduced TLR2 expression in vivo and in vitro, and downregulated expression of myeloid differentiation primary response 88 (MyD88) and phosphorylation of nuclear factor κB (NF-κB). These data demonstrate that Rsv alleviates the ethanol-induced neuroinflammation via inhibition of TLR2-MyD88-NF-κB signal pathway.

Resistin inhibits neuronal autophagy through Toll-like receptor 4

Autophagy is a non-selective degradation pathway induced in energy-deprived cells and in non-starved cells by participating in cellular inflammatory responses mainly through the elimination of injured and aged mitochondria that constitute an important source of reactive oxygen species. We have previously reported that resistin/TLR4 signaling pathway induces inflammation and insulin resistance in neuronal cell. However, the impact of resistin-induced inflammation on neuronal autophagy is unknown. In the present study, we hypothesized that resistin-induced neuroinflammation could be attributed, at least partially, to the impairment of autophagy pathways in neuronal cells. Our data show that resistin decreases neuronal autophagy as evidenced by the repression of the main autophagy markers in SH-SY5Y human neuroblastoma cell line. Furthermore, the silencing of TLR4 completely abolished these effects. Resistin also inhibits AMPK phosphorylation and increases that of Akt/mTOR contrasting with activated autophagy where AMPK phosphorylation is augmented and mTOR inhibited. In vivo, resistin treatment inhibits the mRNA expression of autophagy markers in the hypothalamus of WT mice but not in Tlr4-/- mice. In addition, resistin strongly diminished LC3 (a marker of autophagy) labeling in the arcuate nucleus of WT mice, and this effect is abolished in Tlr4-/- mice. Taken together, our findings clearly reveal resistin/TLR4 as a new regulatory pathway of neuronal autophagy.

Blocking Autophagy in Oligodendrocytes Limits Functional Recovery after Spinal Cord Injury

Autophagy mechanisms are well documented in neurons after spinal cord injury (SCI), but the direct functional role of autophagy in oligodendrocyte (OL) survival in SCI pathogenesis remains unknown. Autophagy is an evolutionary conserved lysosomal-mediated catabolic pathway that ensures degradation of dysfunctional cellular components to maintain homeostasis in response to various forms of stress, including nutrient deprivation, hypoxia, reactive oxygen species, DNA damage, and endoplasmic reticulum (ER) stress. Using pharmacological gain and loss of function and genetic approaches, we investigated the contribution of autophagy in OL survival and its role in the pathogenesis of thoracic contusive SCI in female mice. Although upregulation of Atg5 (an essential autophagy gene) occurs after SCI, autophagy flux is impaired. Purified myelin fractions of contused 8 d post-SCI samples show enriched protein levels of LC3B, ATG5, and BECLIN 1. Data show that, while the nonspecific drugs rapamycin (activates autophagy) and spautin 1 (blocks autophagy) were pharmacologically active on autophagy in vivo, their administration did not alter locomotor recovery after SCI. To directly analyze the role of autophagy, transgenic mice with conditional deletion of Atg5 in OLs were generated. Analysis of hindlimb locomotion demonstrated a significant reduction in locomotor recovery after SCI that correlated with a greater loss in spared white matter. Immunohistochemical analysis demonstrated that deletion of Atg5 from OLs resulted in decreased autophagic flux and was detrimental to OL function after SCI. Thus, our study provides evidence that autophagy is an essential cytoprotective pathway operating in OLs and is required for hindlimb locomotor recovery after thoracic SCI.SIGNIFICANCE STATEMENT This study describes the role of autophagy in oligodendrocyte (OL) survival and pathogenesis after thoracic spinal cord injury (SCI). Modulation of autophagy with available nonselective drugs after thoracic SCI does not affect locomotor recovery despite being pharmacologically active in vivo, indicating significant off-target effects. Using transgenic mice with conditional deletion of Atg5 in OLs, this study definitively identifies autophagy as an essential homeostatic pathway that operates in OLs and exhibits a direct functional role in SCI pathogenesis and recovery. Therefore, this study emphasizes the need to discover novel autophagy-specific drugs that specifically modulate autophagy for further investigation for clinical translation to treat SCI and other CNS pathologies related to OL survival.

Physostigmine Restores Impaired Autophagy in the Rat Hippocampus after Surgery Stress and LPS Treatment

Tissue damage and pathogen invasion during surgical trauma have been identified as contributing factors leading to neuroinflammation in the hippocampus, which can be protected by stimulation of the cholinergic anti-inflammatory pathway using the acetylcholinesterase inhibitor physostigmine. Macroautophagy, an intracellular degradation pathway used to recycle and eliminate damaged proteins and organelles by lysosomal digestion, seems to be important for cell survival under stress conditions. This study aimed to examine the role of autophagy in physostigmine-mediated hippocampal cell protection in a rat model of surgery stress. In the presence or absence of physostigmine, adult Wistar rats underwent surgery in combination with lipopolysaccharide (LPS). Activated microglia, apoptosis-, autophagy-, and anti-inflammatory-related genes and -proteins in the hippocampus were determined by Real-Time PCR, Western blot and fluorescence microscopy after 1 h, 24 h and 3 d. Surgery combined with LPS-treatment led to microglia activation after 1 h and 24 h which was accompanied by apoptotic cell death after 24 h in the hippocampus. Furthermore, it led to a decreased expression of ATG-3 after 24 h and an increased expression of p62/ SQSTM1 after 1 h and 24 h. Administration of physostigmine significantly increased autophagy related markers and restored the autophagic flux after surgery stress, detected by increased degradation of p62/ SQSTM1 in the hippocampus after 1 h and 24 h. Furthermore, physostigmine reduced activated microglia and apoptosis relevant proteins and elevated the increased expression of TGF-beta1 and MFG-E8 after surgery stress. In conclusion, activation of autophagy may be essential in physostigmine-induced neuroprotection against surgery stress.

Anti-neuroinflammatory effects of 20C from Gastrodia elata via regulating autophagy in LPS-activated BV-2 cells through MAPKs and TLR4/Akt/mTOR signaling pathways

20C, a novel bibenzyl compound, is isolated from Gastrodia elata. In our previous study, 20C showed protective effects on tunicamycin-induced endoplasmic reticulum stress, rotenone-induced apoptosis and rotenone-induced oxidative damage. However, the anti-neuroinflammatory effect of 20C is still with limited acquaintance. The objective of this study was to confirm the anti-neuroinflammatory effect of 20C on Lipopolysaccharide (LPS)-activated BV-2 cells and further elucidated the underlying molecular mechanisms. In this study, 20C significantly attenuated the protein levels of nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) and interleukin (IL)-1β, and secretion of nitric oxide (NO) and tumor necrosis factor (TNF)-α induced by Lipopolysaccharide (LPS) in BV-2 cells. Moreover, 20C up-regulated the levels of autophagy-related proteins in LPS-activated BV-2 cells. The requirement of mitogen-activated protein kinases (MAPKs) has been well documented for regulating the process of autophagy. Both 20C and rapamycin enhanced autophagy by suppressing the phosphorylation of MAPKs signaling pathway. Furthermore, 20C treatment significantly inhibited the levels of toll like receptor 4 (TLR4), phosphorylated-protein kinase B (Akt) and phosphorylated-mechanistic target of rapamycin (mTOR), indicating blocking TLR4/Akt/mTOR might be an underlying basis for the anti-inflammatory effect of 20C. These findings suggest that 20C has therapeutic potential for treating neurodegenerative diseases in the future.

Neuregulin 1 Reduces Motoneuron Cell Death and Promotes Neurite Growth in an in Vitro Model of Motoneuron Degeneration

Amyotrophic Lateral Sclerosis (ALS) is a devastating neurodegenerative disorder with no effective treatment currently available. Although the mechanisms of motoneuron (MN) death are still unclear, glutamate excitotoxicity and neuroinflammatory reaction are two main features in the neurodegenerative process of ALS. Neuregulin 1 (NRG1) is a trophic factor highly expressed in MNs and neuromuscular junctions. Several recent evidences suggest that NRG1 and their ErbB receptors are involved in ALS. However, further knowledge is still needed to clarify the role of the NRG1-ErbB pathway on MN survival. In this study we used an in vitro model of spinal cord organotypic cultures (SCOCs) subject to chronic excitotoxicity caused by DL-threo-β-hydroxyaspartic acid (THA) to characterize the effect of NRG1 on MN survival. Our results show that addition of recombinant human NRG1 (rhNRG1) to the medium significantly increased MN survival through the activation of ErbB receptors which was ablated with lapatinib (LP), an ErbB inhibitor, and reduced microglial reactivity overcoming the excitotoxicity effects. rhNRG1 activated the pro-survival PI3K/AKT pathway and restored the autophagic flux in the spinal cord culture. Moreover, addition of rhNRG1 to the medium promoted motor and sensory neurite outgrowth. These findings indicate that increasing NRG1 at the spinal cord is an interesting approach for promoting MN protection and regeneration.

P2X7 Receptor-Associated Programmed Cell Death in the Pathophysiology of Hemorrhagic Stroke

Hemorrhagic stroke is a life-threatening disease characterized by a sudden rupture of cerebral blood vessels, and cell death is widely believed to occur after exposure to blood metabolites or subsequently damaged cells. Recently, programmed cell death, such as apoptosis, autophagy, necroptosis, pyroptosis, and ferroptosis, has been demonstrated to play crucial roles in the pathophysiology of stroke. However, the detailed mechanisms of these novel kinds of cell death are still unclear. The P2X7 receptor, previously known for its cytotoxic activity, is an ATP-gated, nonselective cation channel that belongs to the family of ionotropic P2X receptors. Evolving evidence indicates that the P2X7 receptor plays a pivotal role in central nervous system pathology; genetic deletion and pharmacological blockade of the P2X7 receptor provide neuroprotection in various neurological disorders, including intracerebral hemorrhage and subarachnoid hemorrhage. The P2X7 receptor may regulate programmed cell death via (I) exocytosis of secretory lysosomes, (II) exocytosis of autophagosomes or autophagolysosomes during formation of the initial autophagic isolation membrane or omegasome, and (III) direct release of cytosolic IL-1β secondary to regulated cell death by pyroptosis or necroptosis. In this review, we present an overview of P2X7 receptor- associated programmed cell death for further understanding of hemorrhagic stroke pathophysiology, as well as potential therapeutic targets for its treatment.

CNB-001, a synthetic pyrazole derivative of curcumin, suppresses lipopolysaccharide-induced nitric oxide production through the inhibition of NF-κB and p38 MAPK pathways in microglia

CNB-001, a pyrazole derivative of curcumin, has been found to exert neuroprotective and memory-enhancing effects that may be effective for the treatment of Alzheimer's disease. Since aberrant activation of microglia is involved in the pathogenesis of Alzheimer's disease, the present study was undertaken to investigate the effect of CNB-001 on microglia-mediated inflammatory responses. In primary cultured rat microglia, CNB-001 (1-10µM) suppressed the lipopolysaccharide (LPS)-induced nitric oxide (NO) production and expression of inducible NO synthase (iNOS), and the potency of CNB-001 was stronger than curcumin. CNB-001 also suppressed the LPS-induced nuclear translocation of nuclear factor κB (NF-κB), which is essential for the expression of iNOS. LPS treatment promoted phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK). CNB-001 significantly suppressed the LPS-induced phosphorylation of p38 MAPK, but not ERK and JNK. The suppressive effect of CNB-001 on NO production was mimicked by blockade of the p38 MAPK signaling pathway with SB203580. These results suggest that CNB-001 exerts anti-inflammatory effects through inhibition of NF-κB and p38 MAPK pathways in microglia.

Roflupram, a Phosphodiesterase 4 Inhibitior, Suppresses Inflammasome Activation through Autophagy in Microglial Cells

Inhibition of phosphodiesterase 4 (PDE4) suppressed the inflammatory responses in the brain. However, the underlying mechanisms are poorly understood. Roflupram (ROF) is a novel PDE4 inhibitor. In the present study, we found that ROF enhanced the level of microtubule-associated protein 1 light chain 3 II (LC3-II) and decreased p62 in microglial BV-2 cells. Enhanced fluorescent signals were observed in BV-2 cells treated with ROF by Lysotracker red and acridine orange staining. In addition, immunofluorescence indicated a significant increase in punctate LC3. Moreover, β amyloid 25-35 (Aβ_25-35) or lipopolysaccharide (LPS) with ATP was used to activate inflammasome. We found that both LPS plus ATP and Aβ_25-35 enhanced the conversion of pro-caspase-1 to cleaved-caspase-1 and increased the production of mature IL-1β in BV-2 cells. Interestingly, these effects were blocked by the treatment of ROF. Consistently, knocking down the expression of PDE4B in primary microglial cells led to enhanced level of LC-3 II and decreased activation of inflammasome. What's more, Hoechst staining showed that ROF decreased the apoptosis of neuronal N2a cells in conditioned media from microglia. Our data also showed that ROF dose-dependently enhanced autophagy, reduced the activation of inflammasome and suppressed the production of IL-1β in mice injected with LPS. These effects were reversed by inhibition of microglial autophagy. These results put together demonstrate that ROF inhibits inflammasome activities and reduces the release of IL-1β by inducing autophagy. Therefore, ROF could be used as a potential therapeutic compound for the intervention of inflammation-associated diseases in the brain.

Steroid and Xenobiotic Receptor Signalling in Apoptosis and Autophagy of the Nervous System

Apoptosis and autophagy are involved in neural development and in the response of the nervous system to a variety of insults. Apoptosis is responsible for cell elimination, whereas autophagy can eliminate the cells or keep them alive, even in conditions lacking trophic factors. Therefore, both processes may function synergistically or antagonistically. Steroid and xenobiotic receptors are regulators of apoptosis and autophagy; however, their actions in various pathologies are complex. In general, the estrogen (ER), progesterone (PR), and mineralocorticoid (MR) receptors mediate anti-apoptotic signalling, whereas the androgen (AR) and glucocorticoid (GR) receptors participate in pro-apoptotic pathways. ER-mediated neuroprotection is attributed to estrogen and selective ER modulators in apoptosis- and autophagy-related neurodegenerative diseases, such as Alzheimer’s and Parkinson’s diseases, stroke, multiple sclerosis, and retinopathies. PR activation appeared particularly effective in treating traumatic brain and spinal cord injuries and ischemic stroke. Except for in the retina, activated GR is engaged in neuronal cell death, whereas MR signalling appeared to be associated with neuroprotection. In addition to steroid receptors, the aryl hydrocarbon receptor (AHR) mediates the induction and propagation of apoptosis, whereas the peroxisome proliferator-activated receptors (PPARs) inhibit this programmed cell death. Most of the retinoid X receptor-related xenobiotic receptors stimulate apoptotic processes that accompany neural pathologies. Among the possible therapeutic strategies based on targeting apoptosis via steroid and xenobiotic receptors, the most promising are the selective modulators of the ER, AR, AHR, PPARγ agonists, flavonoids, and miRNAs. The prospective therapies to overcome neuronal cell death by targeting autophagy via steroid and xenobiotic receptors are much less recognized.

Induction of Cell Death by Betulinic Acid through Induction of Apoptosis and Inhibition of Autophagic Flux in Microglia BV-2 Cells

Betulinic acid (BA), a natural pentacyclic triterpene found in many medicinal plants is known to have various biological activity including tumor suppression and anti-inflammatory effects. In this study, the cell-death induction effect of BA was investigated in BV-2 microglia cells. BA was cytotoxic to BV-2 cells with IC₅₀ of approximately 2.0 μM. Treatment of BA resulted in a dose-dependent chromosomal DNA degradation, suggesting that these cells underwent apoptosis. Flow cytometric analysis further confirmed that BA-treated BV-2 cells showed hypodiploid DNA content. BA treatment triggered apoptosis by decreasing Bcl-2 levels, activation of capase-3 protease and cleavage of PARP. In addition, BA treatment induced the accumulation of p62 and the increase in conversion of LC3-I to LC3-II, which are important autophagic flux monitoring markers. The increase in LC3-II indicates that BA treatment induced autophagosome formation, however, accumulation of p62 represents that the downstream autophagy pathway is blocked. It is demonstrated that BA induced cell death of BV-2 cells by inducing apoptosis and inhibiting autophagic flux. These data may provide important new information towards understanding the mechanisms by which BA induce cell death in microglia BV-2 cells.

Rifampicin inhibits rotenone-induced microglial inflammation via enhancement of autophagy

Mitochondrial and autophagic dysfunction, as well as neuroinflammation, are associated with the pathophysiology of Parkinson's disease (PD). Rotenone, an inhibitor of mitochondrial complex I, has been associated as an environmental neurotoxin related to PD. Our previous studies reported that rifampicin inhibited microglia activation and production of proinflammatory mediators induced by rotenone, but the precise mechanism has not been completely elucidated. BV2 cells were pretreated for 2h with rifampicin followed by 0.1μM rotenone, alone or in combination with chloroquine. Here, we demonstrate that rifampicin pretreatment alleviated rotenone induced release of IL-1β and IL-6, and its effects were suppressed when autophagy was inhibited by chloroquine. Moreover, preconditioning with 50μM rifampicin significantly increased viability of SH-SY5Y cells cocultured with rotenone-treated BV2 cells in the transwell coculture system. Chloroquine partially abolished the neuroprotective effects of rifampicin pretreatment. Rifampicin pretreatment significantly reversed rotenone-induced mitochondrial membrane potential reduction and reactive oxygen species accumulation. We suggest that the mechanism for rifampicin-mediated anti-inflammatory and antioxidant effects is the enhancement of autophagy. Indeed, the ratio of LC3-II/LC3-I in rifampicin-pretreated BV2 cells was significantly higher than that in cells without pretreatment. Fluorescence and electron microscopy analyses indicate an increase of lysosomes colocalized with mitochondria in cells pretreated with rifampicin, which confirms that the damaged mitochondria were cleared through autophagy (mitophagy). Taken together, the data provide further evidence that rifampicin exerts neuroprotection against rotenone-induced microglia inflammation, partially through the autophagy pathway. Modulation of autophagy by rifampicin is a novel therapeutic strategy for PD.

P2X7 Receptor Activation Modulates Autophagy in SOD1-G93A Mouse Microglia

Autophagy and inflammation play determinant roles in the pathogenesis of Amyotrophic Lateral Sclerosis (ALS), an adult-onset neurodegenerative disease characterized by deterioration and final loss of upper and lower motor neurons (MN) priming microglia to sustain neuroinflammation and a vicious cycle of neurodegeneration. Given that extracellular ATP through P2X7 receptor constitutes a neuron-to-microglia alarm signal implicated in ALS, and that P2X7 affects autophagy in immune cells, we have investigated if autophagy can be directly triggered by P2X7 activation in primary microglia from superoxide dismutase 1 (SOD1)-G93A mice. We report that P2X7 enhances the expression of the autophagic marker microtubule-associated protein 1 light chain 3 (LC3)-II, via mTOR pathway and concomitantly with modulation of anti-inflammatory M2 microglia markers. We also demonstrate that the autophagic target SQSTM1/p62 is decreased in SOD1-G93A microglia after a short stimulation of P2X7, but increased after a sustained challenge. These effects are prevented by the P2X7 antagonist A-804598, and the autophagy/phosphoinositide-3-kinase inhibitor wortmannin (WM). Finally, a chronic in vivo treatment with A-804598 in SOD1-G93A mice decreases the expression of SQSTM1/p62 in lumbar spinal cord at end stage of disease. These data identify the modulation of the autophagic flux as a novel mechanism by which P2X7 activates ALS-microglia, to be considered for further investigations in ALS.

Neuroinflammation alters cellular proteostasis by producing endoplasmic reticulum stress, autophagy activation and disrupting ERAD activation

Proteostasis alteration and neuroinflammation are typical features of normal aging. We have previously shown that neuroinflammation alters cellular proteostasis through immunoproteasome induction, leading to a transient decrease of proteasome activity. Here, we further investigated the role of acute lipopolysaccharide (LPS)-induced hippocampal neuroinflammation in cellular proteostasis. In particular, we focused on macroautophagy (hereinafter called autophagy) and endoplasmic reticulum-associated protein degradation (ERAD). We demonstrate that LPS injection induced autophagy activation that was dependent, at least in part, on glycogen synthase kinase (GSK)-3β activity but independent of mammalian target of rapamycin (mTOR) inhibition. Neuroinflammation also produced endoplasmic reticulum (ER) stress leading to canonical unfolded protein response (UPR) activation with a rapid activating transcription factor (ATF) 6α attenuation that resulted in a time-dependent down-regulation of ERAD markers. In this regard, the time-dependent accumulation of unspliced X-box binding protein (XBP) 1, likely because of decreased inositol-requiring enzyme (IRE) 1α-mediated splicing activity, might underlie in vivo ATF6α attenuation. Importantly, lactacystin-induced activation of ERAD was abolished in both the acute neuroinflammation model and in aged rats. Therefore, we provide a cellular pathway through which neuroinflammation might sensitize cells to neurodegeneration under stress situations, being relevant in normal aging and other disorders where neuroinflammation is a characteristic feature.

Interplay between Autophagy, Exosomes and HIV-1 Associated Neurological Disorders: New Insights for Diagnosis and Therapeutic Applications

The autophagy–lysosomal pathway mediates a degradative process critical in the maintenance of cellular homeostasis as well as the preservation of proper organelle function by selective removal of damaged proteins and organelles. In some situations, cells remove unwanted or damaged proteins and RNAs through the release to the extracellular environment of exosomes. Since exosomes can be transferred from one cell to another, secretion of unwanted material to the extracellular environment in exosomes may have an impact, which can be beneficial or detrimental, in neighboring cells. Exosome secretion is under the influence of the autophagic system, and stimulation of autophagy can inhibit exosomal release and vice versa. Neurons are particularly vulnerable to degeneration, especially as the brain ages, and studies indicate that imbalances in genes regulating autophagy are a common feature of many neurodegenerative diseases. Cognitive and motor disease associated with severe dementia and neuronal damage is well-documented in the brains of HIV-infected individuals. Neurodegeneration seen in the brain in HIV-1 infection is associated with dysregulation of neuronal autophagy. In this paradigm, we herein provide an overview on the role of autophagy in HIV-associated neurodegenerative disease, focusing particularly on the effect of autophagy modulation on exosomal release of HIV particles and how this interplay impacts HIV infection in the brain. Specific autophagy–regulating agents are being considered for therapeutic treatment and prevention of a broad range of human diseases. Various therapeutic strategies for modulating specific stages of autophagy and the current state of drug development for this purpose are also evaluated.

Microglial Activation in the Pathogenesis of Huntington's Disease

Huntington’s disease (HD) is an autosomal dominantly inherited neurodegenerative disorder caused by expanded CAG trinucleotide repeats (>36) in exon 1 of HTT gene that encodes huntingtin protein. Although HD is characterized by a predominant loss of neurons in the striatum and cortex, previous studies point to a critical role of aberrant accumulation of mutant huntingtin in microglia that contributes to the progressive neurodegeneration in HD, through both cell-autonomous and non-cell-autonomous mechanisms. Microglia are resident immune cells in the central nervous system (CNS), which function to surveil the microenvironment at a quiescent state. In response to various pro-inflammatory stimuli, microglia become activated and undergo two separate phases (M1 and M2 phenotype), which release pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α), anti-inflammatory cytokines, and growth factors (TGF-β, CD206, and Arg1), respectively. Immunoregulation by microglial activation could be either neurotoxic or neuroprotective. In this review, we summarized current understanding about microglial activation in the pathogenesis and progression of HD, with a primary focus of M1 and M2 phenotype of activated microglia and their corresponding signaling pathways.

Mesenchymal stem cells maintain the microenvironment of central nervous system by regulating the polarization of macrophages/microglia after traumatic brain injury

Mesenchymal stem cells (MSCs), which are regarded as promising candidates for cell replacement therapies, are able to regulate immune responses after traumatic brain injury (TBI). Secondary immune response following the mechanical injury is the essential factor leading to the necrosis and apoptosis of neural cells during and after the cerebral edema has subsided and there is lack of efficient agent that can mitigate such neuroinflammation in the clinical application. By means of three molecular pathways (prostaglandin E2 (PGE2), tumor-necrosis-factor-inducible gene 6 protein (TSG-6), and progesterone receptor (PR) and glucocorticoid receptors (GR)), MSCs induce the activation of macrophages/microglia and drive them polarize into the M2 phenotypes, which inhibits the release of pro-inflammatory cytokines and promotes tissue repair and nerve regeneration. The regulation of MSCs and the polarization of macrophages/microglia are dynamically changing based on the inflammatory environment. Under the stimulation of platelet lysate (PL), MSCs also promote the release of pro-inflammatory cytokines. Meanwhile, the statue of macrophages/microglia exerts significant effects on the survival, proliferation, differentiation and activation of MSCs by changing the niche of cells. They form positive feedback loops in maintaining the homeostasis after TBI to relieving the secondary injury and promoting tissue repair. MSC therapies have obtained great achievements in several central nervous system disease clinical trials, which will accelerate the application of MSCs in TBI treatment.

Inhibition of autophagy prevents irradiation-induced neural stem and progenitor cell death in the juvenile mouse brain

Radiotherapy is an effective tool in the treatment of malignant brain tumors. However, damage to brain stem and progenitor cells constitutes a major problem and is associated with long-term side effects. Autophagy has been shown to be involved in cell death, and the purpose of this study was to evaluate the effect of autophagy inhibition on neural stem and progenitor cell death in the juvenile brain. Ten-day-old selective Atg7 knockout (KO) mice and wild-type (WT) littermates were subjected to a single 6Gy dose of whole-brain irradiation. Cell death and proliferation as well as microglia activation and inflammation were evaluated in the dentate gyrus of the hippocampus and in the cerebellum at 6 h after irradiation. We found that cell death was reduced in Atg7 KO compared with WT mice at 6 h after irradiation. The number of activated microglia increased significantly in both the dentate gyrus and the cerebellum of WT mice after irradiation, but the increase was lower in the Atg7 KO mice. The levels of proinflammatory cytokines and chemokines decreased, especially in the cerebellum, in the Atg7 KO group. These results suggest that autophagy might be a potential target for preventing radiotherapy-induced neural stem and progenitor cell death and its associated long-term side effects.

Autophagy and Microglia: Novel Partners in Neurodegeneration and Aging

Autophagy is emerging as a core regulator of Central Nervous System (CNS) aging and neurodegeneration. In the brain, it has mostly been studied in neurons, where the delivery of toxic molecules and organelles to the lysosome by autophagy is crucial for neuronal health and survival. However, we propose that the (dys)regulation of autophagy in microglia also affects innate immune functions such as phagocytosis and inflammation, which in turn contribute to the pathophysiology of aging and neurodegenerative diseases. Herein, we first describe the basic concepts of autophagy and its regulation, discuss key aspects for its accurate monitoring at the experimental level, and summarize the evidence linking autophagy impairment to CNS senescence and disease. We focus on acute, chronic, and autoimmunity-mediated neurodegeneration, including ischemia/stroke, Alzheimer's, Parkinson's, and Huntington's diseases, and multiple sclerosis. Next, we describe the actual and potential impact of autophagy on microglial phagocytic and inflammatory function. Thus, we provide evidence of how autophagy may affect microglial phagocytosis of apoptotic cells, amyloid-β, synaptic material, and myelin debris, and regulate the progression of age-associated neurodegenerative diseases. We also discuss data linking autophagy to the regulation of the microglial inflammatory phenotype, which is known to contribute to age-related brain dysfunction. Overall, we update the current knowledge of autophagy and microglia, and highlight as yet unexplored mechanisms whereby autophagy in microglia may contribute to CNS disease and senescence.

Autophagy down regulates pro-inflammatory mediators in BV2 microglial cells and rescues both LPS and alpha-synuclein induced neuronal cell death

Autophagy is a fundamental cellular homeostatic mechanism, whereby cells autodigest parts of their cytoplasm for removal or turnover. Neurodegenerative disorders are associated with autophagy dysregulation, and drugs modulating autophagy have been successful in several animal models. Microglial cells are phagocytes in the central nervous system (CNS) that become activated in pathological conditions and determine the fate of other neural cells. Here, we studied the effects of autophagy on the production of pro-inflammatory molecules in microglial cells and their effects on neuronal cells. We observed that both trehalose and rapamycin activate autophagy in BV2 microglial cells and down-regulate the production of pro-inflammatory cytokines and nitric oxide (NO), in response to LPS and alpha-synuclein. Autophagy also modulated the phosphorylation of p38 and ERK1/2 MAPKs in BV2 cells, which was required for NO production. These actions of autophagy modified the impact of microglial activation on neuronal cells, leading to suppression of neurotoxicity. Our results demonstrate a novel role for autophagy in the regulation of microglial cell activation and pro-inflammatory molecule secretion, which may be important for the control of inflammatory responses in the CNS and neurotoxicity.

Microglia in Physiology and Disease

As the immune-competent cells of the brain, microglia play an increasingly important role in maintaining normal brain function. They invade the brain early in development, transform into a highly ramified phenotype, and constantly screen their environment. Microglia are activated by any type of pathologic event or change in brain homeostasis. This activation process is highly diverse and depends on the context and type of the stressor or pathology. Microglia can strongly influence the pathologic outcome or response to a stressor due to the release of a plethora of substances, including cytokines, chemokines, and growth factors. They are the professional phagocytes of the brain and help orchestrate the immunological response by interacting with infiltrating immune cells. We describe here the diversity of microglia phenotypes and their responses in health, aging, and disease. We also review the current literature about the impact of lifestyle on microglia responses and discuss treatment options that modulate microglial phenotypes.

Frequency of nuclear mutant huntingtin inclusion formation in neurons and glia is cell-type-specific

Huntington's disease (HD) is an autosomal dominant inherited neurodegenerative disorder that is caused by a CAG expansion in the Huntingtin (HTT) gene, leading to HTT inclusion formation in the brain. The mutant huntingtin protein (mHTT) is ubiquitously expressed and therefore nuclear inclusions could be present in all brain cells. The effects of nuclear inclusion formation have been mainly studied in neurons, while the effect on glia has been comparatively disregarded. Astrocytes, microglia, and oligodendrocytes are glial cells that are essential for normal brain function and are implicated in several neurological diseases. Here we examined the number of nuclear mHTT inclusions in both neurons and various types of glia in the two brain areas that are the most affected in HD, frontal cortex, and striatum. We compared nuclear mHTT inclusion body formation in three HD mouse models that express either full‐length HTT or an N‐terminal exon1 fragment of mHTT, and we observed nuclear inclusions in neurons, astrocytes, oligodendrocytes, and microglia. When studying the frequency of cells with nuclear inclusions in mice, we found that half of the population of neurons contained nuclear inclusions at the disease end stage, whereas the proportion of GFAP‐positive astrocytes and oligodendrocytes having a nuclear inclusion was much lower, while microglia hardly showed any nuclear inclusions. Nuclear inclusions were also present in neurons and all studied glial cell types in human patient material. This is the first report to compare nuclear mHTT inclusions in glia and neurons in different HD mouse models and HD patient brains. GLIA 2016;65:50–61

Actions of the antihistaminergic clemastine on presymptomatic SOD1-G93A mice ameliorate ALS disease progression

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a disease with a strong neuroinflammatory component sustained by activated microglia contributing to motoneuron death. However, how to successfully balance neuroprotective versus neurotoxic actions by the use of antinflammatory agents is still under scrutiny. We have recently shown that the antihistamine clemastine, an FDA-approved drug, can influence the M1/M2 switch occurring in SOD1-G93A ALS microglia.

METHODS

Here, we have chronically treated female SOD1-G93A mice with clemastine, evaluated disease progression and performed mice lumbar spinal cord analysis at symptomatic and end stage of the disease. Moreover, we have studied the mechanism of action of clemastine in primary adult spinal SOD1-G93A microglia cultures and in NSC-G93A motor neuron-like cells.

RESULTS

We found that a short treatment with clemastine (50 mg/kg) from asymptomatic (postnatal day 40) to symptomatic phase (postnatal day 120) significantly delayed disease onset and extended the survival of SOD1-G93A mice by about 10 %. Under these conditions, clemastine induced protection of motor neurons, modulation of inflammatory parameters, reduction of SOD1 protein levels and SQSTM1/p62 autophagic marker, when analysed immediately at the end of the treatment (postnatal day 120). A long treatment with clemastine (from asymptomatic until the end stage) instead failed to ameliorate ALS disease progression. At the end stage of the disease, we found that clemastine short treatment decreased microgliosis and SOD1 protein and increased LC3-II autophagic marker, while the long treatment produced opposite effects. Finally, in spinal microglia cultures from symptomatic SOD1-G93A mice clemastine activated inflammatory parameters, stimulated autophagic flux via the mTOR signalling pathway and decreased SOD1 levels. Modulation of autophagy was also demonstrated in NSC34 SOD1-G93A motor neuron-like cells.

CONCLUSIONS

By gaining insights into the ameliorating actions of an antihistaminergic compound in ALS disease, our findings might represent an exploitable therapeutic approach for familial forms of ALS.

The impact of high and low dose ionising radiation on the central nervous system

Responses of the central nervous system (CNS) to stressors and injuries, such as ionising radiation, are modulated by the concomitant responses of the brains innate immune effector cells, microglia. Exposure to high doses of ionising radiation in brain tissue leads to the expression and release of biochemical mediators of ‘neuroinflammation’, such as pro-inflammatory cytokines and reactive oxygen species (ROS), leading to tissue destruction. Contrastingly, low dose ionising radiation may reduce vulnerability to subsequent exposure of ionising radiation, largely through the stimulation of adaptive responses, such as antioxidant defences. These disparate responses may be reflective of non-linear differential microglial activation at low and high doses, manifesting as an anti-inflammatory or pro-inflammatory functional state. Biomarkers of pathology in the brain, such as the mitochondrial Translocator Protein 18 kDa (TSPO), have facilitated in vivo characterisation of microglial activation and ‘neuroinflammation’ in many pathological states of the CNS, though the exact function of TSPO in these responses remains elusive. Based on the known responsiveness of TSPO expression to a wide range of noxious stimuli, we discuss TSPO as a potential biomarker of radiation-induced effects.

•

Ionising radiation can modulate responses of microglial cells in the CNS.

•

High doses can induce ROS formation, oxidative stress and neuroinflammation.

•

Low doses can mitigate tissue damage via antioxidant defences.

•

TSPO as a potential biomarker and modulator of radiation induced effects in the CNS.

•

Non-linear differential microglial activation to high and low doses is proposed.