An Agonist of the Protective Factor SIRT1 Improves Functional Recovery and Promotes Neuronal Survival by Attenuating Inflammation after Spinal Cord Injury

Brain perivascular macrophages: current understanding and future prospects

Brain perivascular macrophages are specialized populations of macrophages that reside in the space around cerebral vessels, such as penetrating arteries and venules. With the help of cutting-edge technologies, such as cell fate mapping and single-cell multi-omics, their multifaceted, pivotal roles in phagocytosis, antigen presentation, vascular integrity maintenance and metabolic regulation have more recently been further revealed under physiological conditions. Accumulating evidence also implies that perivascular macrophages are involved in the pathogenesis of neurodegenerative disease, cerebrovascular dysfunction, autoimmune disease, traumatic brain injury and epilepsy. They can act in either protective or detrimental ways depending on the disease course and stage. However, the underlying mechanisms of perivascular macrophages remain largely unknown. Therefore, we highlight potential future directions in research on perivascular macrophages, including the utilization of genetic mice and novel therapeutic strategies that target these unique immune cells for neuroprotective purposes. In conclusion, this review provides a comprehensive update on the current knowledge of brain perivascular macrophages, shedding light on their pivotal roles in central nervous system health and disease.

Sirtuins in macrophage immune metabolism: A novel target for cardiovascular disorders

Sirtuins (SIRT1-SIRT7), as a family of NAD+-dependent protein modifying enzymes, have various catalytic functions, such as deacetylases, dealkalylases, and deribonucleases. The Sirtuins family is directly or indirectly involved in pathophysiological processes such as glucolipid metabolism, oxidative stress, DNA repair and inflammatory response through various pathways and assumes an important role in several cardiovascular diseases such as atherosclerosis, myocardial infarction, hypertension and heart failure. A growing number of studies supports that metabolic and bioenergetic reprogramming directs the sequential process of inflammation. Failure of homeostatic restoration leads to many inflammatory diseases, and that macrophages are the central cells involving the inflammatory response and are the main source of inflammatory cytokines. Regulation of cellular metabolism has emerged as a fundamental process controlling macrophage function, but its exact signaling mechanisms remain to be revealed. Understanding the precise molecular basis of metabolic control of macrophage inflammatory processes may provide new approaches for targeting immune metabolism and inflammation. Here, we provide an update of studies in cardiovascular disease on the function and role of sirtuins in macrophage inflammation and metabolism, as well as drug candidates that may interfere with sirtuins, pointing to future prospects in this field.

Adipose tissue-derived mesenchymal stem cells ameliorate cognitive impairment in Alzheimer's disease rat model: Emerging role of SIRT1

Alzheimer's disease (AD) is a complex form of neurodegenerative dementia. Growing body of evidence supports the cardinal role of sirtuin1 (SIRT1) in neurodegeneration and AD development. Recently, adipose tissue-derived mesenchymal stem cells (Ad-MSCs) have made their mark for a wide array of regenerative medicine applications, including neurodegenerative disorders. Therefore, the present study aimed to investigate the therapeutic potential of Ad-MSCs in AD rat model, and to explore the possible implication of SIRT1. Ad-MSCs were isolated from rat epididymal fat pads and properly characterized. Aluminum chloride was used to induce AD in rats, and afterward, a group of AD-induced rats received a single dose of Ad-MSCs (2 × 106 cell, I.V per rat). One month after Ad-MSCs transplantation, behavioral tests were done, brain tissues were collected, then histopathological and biochemical assessments were performed. Amyloid beta and SIRT1 levels were determined by enzyme-linked immunosorbent assay. Whereas expression levels of neprilysin, BCL2 associated X protein, B-cell lymphoma-2, interleukin-1β, interleukin-6, and nerve growth factor in hippocampus and frontal cortex brain tissues were assessed using reverse transcriptase quantitative polymerase chain reaction. Our data demonstrated that transplantation of Ad-MSCs alleviated cognitive impairment in AD rats. Additionally, they exhibited anti-amyloidogenic, antiapoptotic, anti-inflammatory, as well as neurogenic effects. Furthermore, Ad-MSCs were found to possibly mediate their therapeutic effects, at least partially, via modulating both central and systemic SIRT1 levels. Hence, the current study portrays Ad-MSCs as an effective therapeutic approach for AD management and opens the door for future investigations to further elucidate the role of SIRT1 and its interrelated molecular mediators in AD.

Elevation of NAD+ by nicotinamide riboside spares spinal cord tissue from injury and promotes locomotor recovery

Spinal cord injury (SCI)-induced tissue damage spreads to neighboring spared cells in the hours, days, and weeks following injury, leading to exacerbation of tissue damage and functional deficits. Among the biochemical changes is the rapid reduction of cellular nicotinamide adenine dinucleotide (NAD+), an essential coenzyme for energy metabolism and an essential cofactor for non-redox NAD+-dependent enzymes with critical functions in sensing and repairing damaged tissue. NAD+ depletion propagates tissue damage. Augmenting NAD+ by exogenous application of NAD+, its synthesizing enzymes, or its cellular precursors mitigates tissue damage. Nicotinamide riboside (NR) is considered to be one of the most promising NAD+ precursors for clinical application due to its ability to safely and effectively boost cellular NAD+ synthesis in rats and humans. Moreover, various preclinical studies have demonstrated that NR can provide tissue protection. Despite these promising findings, little is known about the potential benefits of NR in the context of SCI. In the current study, we tested whether NR administration could effectively increase NAD+ levels in the injured spinal cord and whether this augmentation of NAD+ would promote spinal cord tissue protection and ultimately lead to improvements in locomotor function. Our findings indicate that administering NR (500 mg/kg) intraperitoneally from four days before to two weeks after a mid-thoracic contusion-SCI injury, effectively doubles NAD+ levels in the spinal cord of Long-Evans rats. Moreover, NR administration plays a protective role in preserving spinal cord tissue post-injury, particularly in neurons and axons, as evident from the observed gray and white matter sparing. Additionally, it enhances motor function, as evaluated through the BBB subscore and missteps on the horizontal ladderwalk. Collectively, these findings demonstrate that administering NR, a precursor of NAD+, increases NAD+ within the injured spinal cord and effectively mitigates the tissue damage and functional decline that occurs following SCI.

SIRT1 attenuates blood-spinal cord barrier disruption after spinal cord injury by deacetylating p66Shc

Disruption of the blood-spinal cord barrier (BSCB) leads to inflammatory cell infiltration and neural cell death, thus, contributing to poor functional recovery after spinal cord injury (SCI). Previous studies have suggested that Sirtuin 1 (SIRT1), an NAD⁺-dependent class III histone deacetylase, is abundantly expressed in endothelial cells and promotes endothelial homeostasis. However, the role of SIRT1 in BSCB function after SCI remains poorly defined. Here, we report that SIRT1 is highly expressed in spinal cord endothelial cells, and its expression significantly decreases after SCI. Using endothelial cell-specific SIRT1 knockout mice, we observed that endothelial cell-specific knockout of SIRT1 aggravated BSCB disruption, thus, resulting in widespread inflammation, neural cell death and poor functional recovery after SCI. In contrast, activation of SIRT1 by the agonist SRT1720 had beneficial effects. In vitro, knockdown of SIRT1 exacerbated IL-1β-induced endothelial barrier disruption in bEnd.3 cells, whereas overexpression of SIRT1 was protective. Using RNA-seq and IP/MS analysis, we identified p66Shc, a redox protein, as the potential target of SIRT1. Further studies demonstrated that SIRT1 interacts with and deacetylates p66Shc, thereby attenuating oxidative stress and protecting endothelial barrier function. Overall, our results indicate that SIRT1 decreases endothelial ROS production and attenuates BSCB disruption by deacetylating p66Shc after SCI, and suggest that SIRT1 activation has potential as a therapeutic approach to promote functional recovery against BSCB disruption following SCI.

Adipose-derived mesenchymal stem cells overexpressing prion improve outcomes via the NLRP3 inflammasome/DAMP signalling after spinal cord injury in rat

Traumatic spinal cord injury (SCI) is a highly destructive disease in human neurological functions. Adipose-derived mesenchymal stem cells (ADMSCs) have tissue regenerations and anti-inflammations, especially with prion protein overexpression (PrPc^OE ). Therefore, this study tested whether PrPc^OE -ADMSCs therapy offered benefits in improving outcomes via regulating nod-like-receptor-protein-3 (NLRP3) inflammasome/DAMP signalling after acute SCI in rats. Compared with ADMSCs only, the capabilities of PrPc^OE -ADMSCs were significantly enhanced in cellular viability, anti-oxidative stress and migration against H₂ O₂ and lipopolysaccharide damages. Similarly, PrPc^OE -ADMSCs significantly inhibited the inflammatory patterns of Raw264.7 cells. The SD rats (n = 32) were categorized into group 1 (Sham-operated-control), group 2 (SCI), group 3 (SCI + ADMSCs) and group 4 (SCI + PrPc^OE -ADMSCs). Compared with SCI group 2, both ADMSCs and PrPc^OE -ADMSCs significantly improved neurological functions. Additionally, the circulatory inflammatory cytokines levels (TNF-α/IL-6) and inflammatory cells (CD11b/c+/MPO+/Ly6G+) were highest in group 2, lowest in group 1, and significantly higher in group 3 than in group 4. By Day 3 after SCI induction, the protein expressions of inflammasome signalling (HGMB1/TLR4/MyD88/TRIF/c-caspase8/FADD/p-NF-κB/NEK7/NRLP3/ASC/c-caspase1/IL-ß) and by Day 42 the protein expressions of DAMP-inflammatory signalling (HGMB1/TLR-4/MyD88/TRIF/TRAF6/p-NF-κB/TNF-α/IL-1ß) in spinal cord tissues displayed an identical pattern as the inflammatory patterns. In conclusion, PrPc^OE -ADMSCs significantly attenuated SCI in rodents that could be through suppressing the inflammatory signalling.

Outcomes of RIP Kinase Signaling During Neuroinvasive Viral Infection

Neuroinvasive viral diseases are a considerable and growing burden on global public health. Despite this, these infections remain poorly understood, and the molecular mechanisms that govern protective versus pathological neuroinflammatory responses to infection are a matter of intense investigation. Recent evidence suggests that necroptosis, an immunogenic form of programmed cell death, may contribute to the pathogenesis of viral encephalitis. However, the receptor-interacting protein (RIP) kinases that coordinate necroptosis, RIPK1 and RIPK3, also appear to have unexpected, cell death-independent functions in the central nervous system (CNS) that promote beneficial neuroinflammation during neuroinvasive infection. Here, we review the emerging evidence in this field, with additional discussion of recent work examining roles for RIPK signaling and necroptosis during noninfectious pathologies of the CNS, as these studies provide important additional insight into the potential for specialized neuroimmune functions for the RIP kinases.

MicroRNA-451 Attenuates the Inflammatory Response of Activated Microglia by Downregulating Nucleotide Binding Oligomerization Domain-Like Receptor Protein 3

BACKGROUND

Spinal cord injury is the most common problem encountered during spinal surgery. After the initial trauma, the disruption of the blood-brain barrier and subsequent microglia activation result in extensive inflammatory responses. Inflammasomes are large protein complexes that are essential during inflammation. One of the most studied inflammasome components, nucleotide binding oligomerization domain-like receptor protein 3 (NLRP; nucleotide binding oligomerization domain-, leucine-rich repeat-, and pyrin domain-containing 3), is widely expressed in the central nervous system. Previous research has shown that microRNA-451 (miR-451) might play a role in regulating inflammatory conditions.

METHODS

Using bioinformatics analysis, we found that NLRP3 is a direct target of miR-451. This in silico prediction was confirmed using dual-luciferase reporter gene assays. To further demonstrate that miR-451 influenced microglial NLRP3 production, we activated microglial cells with lipopolysaccharides.

RESULTS

Activating microglial cells with lipopolysaccharides resulted in the production of NLRP3 inflammasomes and the secretion of the proinflammatory cytokines interleukin-1β and interleukin-18. We were able to demonstrate that overexpression of miR-451 suppressed this NLRP3-induced proinflammatory cascade of events.

CONCLUSIONS

Our findings have highlighted the potential anti-inflammatory role of miR-451 in reducing the secondary neuronal damage after spinal cord injury.

Immunoengineering strategies to enhance vascularization and tissue regeneration

Immune cells have emerged as powerful regulators of regenerative as well as pathological processes. The vast majority of regenerative immunoengineering efforts have focused on macrophages; however, growing evidence suggests that other cells of both the innate and adaptive immune system are as important for successful revascularization and tissue repair. Moreover, spatiotemporal regulation of immune cells and their signaling have a significant impact on the regeneration speed and the extent of functional recovery. In this review, we summarize the contribution of different types of immune cells to the healing process and discuss ways to manipulate and control immune cells in favor of vascularization and tissue regeneration. In addition to cell delivery and cell-free therapies using extracellular vesicles, we discuss in situ strategies and engineering approaches to attract specific types of immune cells and modulate their phenotypes. This field is making advances to uncover the extraordinary potential of immune cells and their secretome in the regulation of vascularization and tissue remodeling. Understanding the principles of immunoregulation will help us design advanced immunoengineering platforms to harness their power for tissue regeneration.

Neuroprotective Potential of Dendritic Cells and Sirtuins in Multiple Sclerosis

Myeloid cells, including parenchymal microglia, perivascular and meningeal macrophages, and dendritic cells (DCs), are present in the central nervous system (CNS) and establish an intricate relationship with other cells, playing a crucial role both in health and in neurological diseases. In this context, DCs are critical to orchestrating the immune response linking the innate and adaptive immune systems. Under steady-state conditions, DCs patrol the CNS, sampling their local environment and acting as sentinels. During neuroinflammation, the resulting activation of DCs is a critical step that drives the inflammatory response or the resolution of inflammation with the participation of different cell types of the immune system (macrophages, mast cells, T and B lymphocytes), resident cells of the CNS and soluble factors. Although the importance of DCs is clearly recognized, their exact function in CNS disease is still debated. In this review, we will discuss modern concepts of DC biology in steady-state and during autoimmune neuroinflammation. Here, we will also address some key aspects involving DCs in CNS patrolling, highlighting the neuroprotective nature of DCs and emphasizing their therapeutic potential for the treatment of neurological conditions. Recently, inhibition of the NAD⁺-dependent deac(et)ylase sirtuin 6 was demonstrated to delay the onset of experimental autoimmune encephalomyelitis, by dampening DC trafficking towards inflamed LNs. Thus, a special focus will be dedicated to sirtuins’ role in DCs functions.

Effect of Sirtuin-1 and Wnt/β-Catenin Signaling Pathway in Rat Model of Spinal Cord Injury

Sirtuin-1 (SIRT1) has anti-inflammatory and antioxidant effects and has been reported to be involved in spinal cord injury (SCI). Wnt/β-catenin signal has been shown to play a critical role in the pathogenesis of chronic diseases, and it participated in the recovery of nerve function after SCI. However, the specific link between them in SCI is unclear. In addition, targeting posttraumatic astrocyte apoptosis is crucial for improving neural degeneration and locomotor function. Therefore, in this article, we studied the relationship of β-catenin and SIRT1 using in the SCI rat model and primary astrocyte treated with hydrogen peroxide (H2O2) or lithium chloride (LiCl). Results showed that after SCI, SCI area and motor function recover over time, and β-catenin is gradually increased to the seventh day and then in turn decreases until 4 weeks, positively correlated with cell apoptosis. The expression of SIRT1 and downstream FOXO4 gradually increased, and β-catenin is negatively correlated with SIRT1 expression. Moreover, treatment with H2O2 in primary cultured astrocyte significantly increased β-catenin and Caspase-3 expression, while decreased SIRT1 and Forkhead box O- (FOXO-) 4. The immunofluorescence results are consistent with this. Administration of LiCl further aggravates the above results. These findings suggest that SIRT1 is negatively correlated with β-catenin in SCI, which promotes the apoptosis of motor neuron cells, which may be related to the participation of FOXO4.

Deciphering therapeutic options for neurodegenerative diseases: insights from SIRT1

Silent information regulator 1 (SIRT1) is a nicotinamide adenine dinucleotide (NAD +)-dependent protein deacetylase that exerts biological effects through nucleoplasmic transfer. Recent studies have highlighted that SIRT1 deacetylates protein substrates to exert its neuroprotective effects, including decreased oxidative stress and inflammatory, increases autophagy, increases levels of nerve growth factors (correlated with behavioral changes), and maintains neural integrity (affects neuronal development and function) in aging or neurological disorder. In this review, we highlight the molecular mechanisms underlying the protective role of SIRT1 in modulating neurodegeneration, focusing on protein homeostasis, aging-related signaling pathways, neurogenesis, and synaptic plasticity. Meanwhile, the potential of targeting SIRT1 to block the occurrence and progression of neurodegenerative diseases is also discussed. Taken together, this review provides an up-to-date evaluation of our current understanding of the neuroprotective mechanisms of SIRT1 and also be involved in the potential therapeutic opportunities of AD and related neurodegenerative diseases.

MicroRNA-155-5p promotes neuroinflammation and central sensitization via inhibiting SIRT1 in a nitroglycerin-induced chronic migraine mouse model

Background

Previous studies have confirmed that the microglial activation and subsequent inflammatory responses in the trigeminal nucleus caudalis (TNC) are involved in the central sensitization of chronic migraine (CM). MicroRNA-155-5p has been shown to modulate the polarization of microglia and participate in inflammatory processes in a variety of neurological diseases. However, its role in CM remains unclear. The purpose of this study was to determine the precise role of miR-155-5p in CM.

Methods

A model of CM in C57BL/6 mice was established by recurrent intraperitoneal injection of nitroglycerin (NTG). Mechanical and thermal hyperalgesia were evaluated by Von Frey filaments and radiant heat. The expression of miR-155-5p was examined by qRT-PCR, and the mRNA and protein levels of silent information regulator 1(SIRT1) were measured by qRT-PCR, Western blotting (WB) and immunofluorescence (IF) analysis. The miR-155-5p antagomir, miR-155-5p agomir, SRT1720 (a SIRT1 activator) and EX527 (a SIRT1 inhibitor) were administered to confirm the effects of miR-155-5p and SIRT1 on neuroinflammation and the central sensitization of CM. ELISA, WB and IF assays were applied to evaluate the expression of TNF-α, myeloperoxidase (MPO), IL-10, p-ERK, p-CREB, calcitonin gene-related peptide (CGRP), c-Fos and microglial activation. The cellular localization of SIRT1 was illustrated by IF.

Results

After the NTG-induced mouse model of CM was established, the expression of miR-155-5p was increased. The level of SIRT1 was decreased, and partly colocalized with Iba1 in the TNC. The miR-155-5p antagomir and SRT1720 downregulated the expression of p-ERK, p-CREB, CGRP, and c-Fos, alleviating microglial activation and decreasing inflammatory substances (TNF-α, MPO). The administration of miR-155-5p agomir or EX527 exacerbated neuroinflammation and central sensitization. Importantly, the miR-155-5p agomir elevated CGRP and c-Fos expression and microglial activation, which could subsequently be alleviated by SRT1720.

Conclusions

These data demonstrate that upregulated miR-155-5p in the TNC participates in the central sensitization of CM. Inhibiting miR-155-5p alleviates neuroinflammation by activating SIRT1 in the TNC of CM mice.

Neural Stem Cells: Promoting Axonal Regeneration and Spinal Cord Connectivity

Spinal cord injury (SCI) leads to irreversible functional impairment caused by neuronal loss and the disruption of neuronal connections across the injury site. While several experimental strategies have been used to minimize tissue damage and to enhance axonal growth and regeneration, the corticospinal projection, which is the most important voluntary motor system in humans, remains largely refractory to regenerative therapeutic interventions. To date, one of the most promising pre-clinical therapeutic strategies has been neural stem cell (NSC) therapy for SCI. Over the last decade we have found that host axons regenerate into spinal NSC grafts placed into sites of SCI. These regenerating axons form synapses with the graft, and the graft in turn extends very large numbers of new axons from the injury site over long distances into the distal spinal cord. Here we discuss the pathophysiology of SCI that makes the spinal cord refractory to spontaneous regeneration, the most recent findings of neural stem cell therapy for SCI, how it has impacted motor systems including the corticospinal tract and the implications for sensory feedback.

SIRT1 Promotes M2 Microglia Polarization via Reducing ROS-Mediated NLRP3 Inflammasome Signaling After Subarachnoid Hemorrhage

Mounting evidence has suggested that modulating microglia polarization from pro-inflammatory M1 phenotype to anti-inflammatory M2 state might be a potential therapeutic approach in the treatment of subarachnoid hemorrhage (SAH) injury. Our previous study has indicated that sirtuin 1 (SIRT1) could ameliorate early brain injury (EBI) in SAH by reducing oxidative damage and neuroinflammation. However, the effects of SIRT1 on microglial polarization and the underlying molecular mechanisms after SAH have not been fully illustrated. In the present study, we first observed that EX527, a potent selective SIRT1 inhibitor, enhanced microglial M1 polarization and nod-like receptor pyrin domain-containing 3 (NLRP3) inflammasome activation in microglia after SAH. Administration of SRT1720, an agonist of SIRT1, significantly enhanced SIRT1 expression, improved functional recovery, and ameliorated brain edema and neuronal death after SAH. Moreover, SRT1720 modulated the microglia polarization shift from the M1 phenotype and skewed toward the M2 phenotype. Additionally, SRT1720 significantly decreased acetylation of forkhead box protein O1, inhibited the overproduction of reactive oxygen species (ROS) and suppressed NLRP3 inflammasome signaling. In contrast, EX527 abated the upregulation of SIRT1 and reversed the inhibitory effects of SRT1720 on ROS-NLRP3 inflammasome activation and EBI. Similarly, in vitro, SRT1720 suppressed inflammatory response, oxidative damage, and neuronal degeneration, and improved cell viability in neurons and microglia co-culture system. These effects were associated with the suppression of ROS-NLRP3 inflammasome and stimulation of SIRT1 signaling, which could be abated by EX527. Altogether, these findings indicate that SRT1720, an SIRT1 agonist, can ameliorate EBI after SAH by shifting the microglial phenotype toward M2 via modulation of ROS-mediated NLRP3 inflammasome signaling.

SIRT1 Protects Dopaminergic Neurons in Parkinson's Disease Models via PGC-1α-Mediated Mitochondrial Biogenesis

SIRT1 is a deacetylase with multiple physiological functions by targeting histones and non-histone proteins. It has been shown that SIRT1 activation is involved in neuroprotection in Parkinson's disease (PD) models. In the present study, we provided direct evidences showing the neuroprotective roles of SIRT1 in dopaminergic neurons. Our data showed that increased expression of SIRT1 plays beneficial roles against MPP⁺ insults in SH-SY5Y cells and primary dopaminergic neurons, including increased cell viability, reduced LDH release, improved the mitochondrial membrane potential (MMP), and attenuated cell apoptosis. On the contrary, knockdown of SIRT1 further aggravated cell injuries induced by MPP⁺. Moreover, mutated SIRT1 without deacetylase activity (SIRT1 H363Y) failed to protect dopaminergic neurons from MPP⁺ injuries. Mechanistically, SIRT1 improved PGC-1α expression and mitochondrial biogenesis. Knockdown of PGC-1α almost completely abolished the neuroprotective roles of SIRT1 in SH-SY5Y cells. Collectively, our data indicate that SIRT1 has neuroprotective roles in dopaminergic neurons, which is dependent upon PGC-1α-mediated mitochondrial biogenesis. These findings suggest that SIRT1 may hold great therapeutic potentials for treating dopaminergic neuron loss associated disorders such as PD.

Role of SIRT1 in Neuropathic Pain from the Viewpoint of Neuroimmunity

The current clinical first-line treatment of neuropathic pain still considers only the nervous system as the target, and its therapeutic effect is limited. An increasing number of studies support the opinion that neuropathic pain is a result of the combined action of the sensory nervous system and the related immune system. Under physiological conditions, both the nervous system and the immune system can maintain homeostasis by adjusting the mitochondrial function when sensing noxious stimulation. However, in the case of neuropathic pain, mitochondrial regulatory dysfunction occurs, which may result from the decreased expression of SIRT1. In this study, we review the role of SIRT1 in neuropathic pain from the viewpoint of neuroimmunity.

Sirtuins: Potential Therapeutic Targets for Defense against Oxidative Stress in Spinal Cord Injury

Spinal cord injury (SCI) is one of the most incapacitating neurological disorders. It involves complex pathological processes that include a primary injury and a secondary injury phase, or a delayed stage, which follows the primary injury and contributes to the aggravation of the SCI pathology. Oxidative stress, a key pathophysiological event after SCI, contributes to a cascade of inflammation, excitotoxicity, neuronal and glial apoptosis, and other processes during the secondary injury phase. In recent years, increasing evidence has demonstrated that sirtuins are protective toward the pathological process of SCI through a variety of antioxidant mechanisms. Notably, strategies that modulate the expression of sirtuins exert beneficial effects in cellular and animal models of SCI. Given the significance and novelty of sirtuins, we summarize the oxidative stress processes that occur in SCI and discuss the antioxidant effects of sirtuins in SCI. We also highlight the potential of targeting sirtuins for the treatment of SCI.

The Serum SIRT1 Protein is Associated with the Severity of Injury and Neurological Recovery in Mice with Traumatic Spinal Cord Injury

The present study aimed to investigate the association between the serum SIRT1 protein and the severity of spinal cord injury (SCI) as well as the neurological recovery in mice. In this study, the wild-type (WT), Mx1-Cre⁺ SIRT1^loxP/loxP (Mx1), and LCK-Cre⁺SIRT1^loxP/loxP (LCK) mice were subjected to sham surgery, mild, moderate, or severe SCI, respectively. The serum was collected at intervals of 12 h, 1 day (d), 3 d, 5 d, 7 d, 10 d, 14 d, and 21 d after the injury. The locomotor function of all the animals was assessed using the Basso mouse scale (BMS) and the serum SIRT1 proteins were analyzed using enzyme-linked immunosorbent assay (ELISA). The results demonstrated that about 7-10 d after SCI, the levels of SIRT1 protein in the serum correlated significantly with the severity of the injury and at 28 d post-injury, there was a distant neurological recovery (BMS score). The serum SIRT1 concentration in both the Mx1 and LCK mice in the sham group was significantly reduced compared to that in the WT mice, and there was a delayed increase in the serum SIRT1 levels after injury. These findings indicate that the SIRT1 concentrations in the serum of the SCI mice closely correlated with the acute severity and neurological outcome.

Silencing of miR-324-5p alleviates rat spinal cord injury by Sirt1

MicroRNAs (miRNAs) are implicated in the pathogenesis of spinal cord injury (SCI) as primary regulators. Previous studies have reported that miR-324-5p is involved in the modulation of neural injury, while the underlying mechanisms of miR-324-5p in SCI remain unclear. In a SCI rat model, miR-324-5p was significantly upregulated in the spinal cord tissues after SCI. Downregulation of miR-324-5p via injection of adeno-associated viruses (AAV) expressing miR-324-5p inhibitor relieved animal motor deficits and pathological changes in the tissues. Furthermore, downregulation of miR-324-5p significantly altered the expression of genes regulating neural growth, apoptosis, and the inflammatory and antioxidant response, which are implicated in SCI pathogenesis. In a H₂O₂-induced cell injury model, miR-324-5p silencing rescued the elevated apoptosis of PC12 cells. Finally, miR-324-5p directly targeted the 3'-untranslated region of NAD-dependent protein deacetylase sirtuin-1 (Sirt1) and negatively regulated the levels of Sirt1, an anti-inflammatory protein involved in SCI. Silencing of Sirt1 aggravated SCI and rescued the effects of miR-324-5p downregulation in rats. Overall, our findings indicated that silencing of miR-324-5p alleviates the loss of animal locomotion and concurrently mediates several degenerative processes relevant to the pathogenesis of SCI by Sirt1, which may provide clues for SCI treatment.

Difference of pain vulnerability in adult and juvenile rodents: the role of SIRT1-mediated ClC-3 trafficking in sensory neurons

ABSTRACT

Adults are more likely to suffer from chronic pain than minors, and its underlying mechanism remains unclear. SIRT1 an important age-related protein with function of lifespan extension; whether SIRT1 plays a role in the different pain vulnerability of adult and juvenile remains unclear. Here, we found that the expression level of SIRT1 in dorsal root ganglia (DRG) was related to the pain vulnerability. After nerve injury, the expression of SIRT1 in DRG was decreased in adult rodents whereas increased in juvenile rodents. Differential manipulation of SIRT1 abolished the different pain vulnerability between adult and juvenile rodents. Furthermore, SIRT1 interacted with ClC-3 channel and mediated ClC-3 membrane trafficking and Cl- current in DRG neurons. Differential manipulation of ClC-3 also abolished the difference in pain vulnerability between adult and juvenile rodents. The different anti-inflammatory ability determined the different change trends of SIRT1 and ClC-3 trafficking contributed to the different pain vulnerability in adult and juvenile rodents. In addition, the serum SIRT1 level was negatively correlated with the pain score in patients with chronic pain. These findings revealed the mechanism of the difference in pain vulnerability between adult and juvenile rodents and provided evidence for age-specific treatment of chronic pain.

Bone marrow mesenchymal stem cells-derived exosomes reduce apoptosis and inflammatory response during spinal cord injury by inhibiting the TLR4/MyD88/NF-κB signaling pathway

Spinal cord injury (SCI) is one of the most common destructive injuries, which may lead to permanent neurological dysfunction. Currently, transplantation of bone marrow mesenchymal stem cells (BMSCs) in experimental models of SCI shows promise as effective therapies. BMSCs secrete various factors that can regulate the microenvironment, which is called paracrine effect. Among these paracrine substances, exosomes are considered to be the most valuable therapeutic factors. Our study found that BMSCs-derived exosomes therapy attenuated cell apoptosis and inflammation response in the injured spinal cord tissues. In in vitro studies, BMSCs-derived exosomes significantly inhibited lipopolysaccharide (LPS)-induced PC12 cell apoptosis, reduced the secretion of pro-inflammatory factors including tumor necrosis factor (TNF)-α and IL (interleukin)-1β and promoted the secretion of anti-inflammatory factors including IL-10 and IL-4. Moreover, we found that LPS-induced protein expression of toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (MyD88) and nuclear transcription factor-κB (NF-κB) was significantly downregulated after treatment with BMSCs-derived exosomes. In in vivo studies, we found that hindlimb motor function was significantly improved in SCI rats with systemic administration of BMSCs-derived exosomes. We also observed that the expression of pro-apoptotic proteins and pro-inflammatory factors was significantly decreased, while the expression of anti-apoptotic proteins and anti-inflammatory factors were upregulated in SCI rats after exosome treatment. In conclusion, BMSCs-derived exosomes can inhibit apoptosis and inflammation response induced by injury and promote motor function recovery by inhibiting the TLR4/MyD88/NF-κB signaling pathway, which suggests that BMSCs-derived exosomes are expected to become a new therapeutic strategy for SCI.

MicroRNA-92a-3p enhances functional recovery and suppresses apoptosis after spinal cord injury via targeting phosphatase and tensin homolog

Spinal cord injury (SCI) is a neurological disease commonly caused by traumatic events on spinal cords. MiRNA-92a-3p is reported to be down-regulated after SCI. Our study investigated the effects of up-regulated miR-92a-3p on SCI and the underlying mechanisms. SCI mice model was established to evaluate the functional recovery of hindlimbs of mice through open-field locomotion and scored by Basso, Beattie, and Bresnahan (BBB) locomotion scale. Apoptosis of spinal cord cells was determined by flow cytometry. The effects of miR-92a-3p on SCI were detected by intrathecally injecting miR-92a-3p agomiR (agomiR-92) into the mice prior to the establishment of SCI. Phosphatase and tensin homolog (PTEN) was predicted as a target of miR-29a-3p by TargetScan. We further assessed the effects of agomiR-92 or/and overexpressed PTEN on apoptosis rates and apoptotic protein expressions in SCI mice. Moreover, the activation of protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling was determined by Western blot. The results showed that compared with the sham-operated mice, SCI mice had much lower BBB scores, and theapoptosis rate of spinal cord cells was significantly increased. After SCI, the expression of miR-92a-3p was down-regulated, and increased expression of miR-92a-3p induced by agomiR-92 further significantly increased the BBB score and decreased apoptosis. PTEN was specifically targeted by miR-92a-3p. In addition, the phosphorylation levels of Akt and mTOR were up-regulated under the treatment of agomiR-92. Our data demonstrated that the neuroprotective effects of miR-92a-3p on spinal cord safter SCI were highly associated with the activation of the PTEN/AKT/mTOR pathway.

Sirtuins and Their Implications in Neurodegenerative Diseases from a Drug Discovery Perspective

Sirtuins are class III histone deacetylase (HDAC) enzymes that target both histone and non-histone substrates. They are linked to different brain functions and the regulation of different isoforms of these enzymes is touted to be an emerging therapy for the treatment of neurodegenerative diseases (NDs), including Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). The level of sirtuins affects brain health as many sirtuin-regulated pathways are responsible for the progression of NDs. Certain sirtuins are also implicated in aging, which is a risk factor for many NDs. In addition to SIRT1-3, it has been suggested that the less studied sirtuins (SIRT4-7) also play critical roles in brain health. This review delineates the role of each sirtuin isoform in NDs from a disease centric perspective and provides an up-to-date overview of sirtuin modulators and their potential use as therapeutics in these diseases. Furthermore, the future perspectives for sirtuin modulator development and their therapeutic application in neurodegeneration are outlined in detail, hence providing a research direction for future studies.

Roflupram, a novel phosphodiesterase 4 inhibitor, inhibits lipopolysaccharide-induced neuroinflammatory responses through activation of the AMPK/Sirt1 pathway

Roflupram (ROF) is a novel phosphodiesterase 4 inhibitor. We previously found that ROF suppressed the production of pro-inflammatory factors in microglial cells; however, the underlying mechanisms are largely unknown. The present study aimed to elucidate the underlying molecular mechanisms of the anti-neuroinflammatory effects of ROF in lipopolysaccharide (LPS)-activated microglial cells and LPS-challenged mice. Treatment with ROF suppressed LPS-induced expression of interleukin (IL)-6 and tumor necrosis factor (TNF)-α in BV-2 microglia cell line. Immunofluorescence and Western blotting analysis showed that ROF significantly inhibited the activation of microglia, as evidenced by decreased expression of ionized calcium binding adaptor molecule-1 (Iba1). Similar results were obtained in primary cultured microglial cells. ROF induced the phosphorylation of AMP-activated protein kinase (AMPK) and the expression of Sirtuin 1 (Sirt1). Interestingly, the AMPK inhibitor, compound C, blocked the role of ROF in both the phosphorylation of AMPK and the expression of Sirt1 in BV-2 cells stimulated with LPS. More importantly, the Sirt1 inhibitor, EX527, abolished the inhibitory role of ROF on the production of pro-inflammatory factors, and reactivated BV-2 cells. In mice challenged with LPS, ROF improved cognition and decreased the levels of IL-6 and TNF-α in both the cortex and hippocampus. In contrast, EX527 weakened the effects of ROF on cognitive enhancement and reduction of pro-inflammatory factors in the cortex and hippocampus. Furthermore, EX527 blocked the inhibitory role of ROF in the activation of microglial cells in both the hippocampus and cortex. Taken together, our results indicated that ROF attenuated LPS-induced neuroinflammatory responses in microglia, and the AMPK/Sirt1 pathway is essential for the anti-inflammatory effects of ROF.

Autophagy Induction Contributes to the Neuroprotective Impact of Intermittent Fasting on the Acutely Injured Spinal Cord

Spinal cord injury (SCI) is one of the leading causes of neurological disability and death. So far, there is no satisfactory treatment for SCI, because of its complex and ill-defined pathophysiology. Recently, autophagy has been implicated as protective in acute SCI rat models. Here, we investigated the therapeutic value of a dietary intervention, namely, intermittent fasting (IF), on neuronal survival after acute SCI in rats, and its underlying mechanism related to autophagy regulation. We found remarkable improvement in both behavioral performance and neuronal survival at the injured segment of the spinal cord of animals previously subjected to IF. Western blotting revealed a marked decrease in apoptosis-related markers such as cleaved caspase 3 levels and the bax/bcl-2 ratio in the IF group, which suggested an inhibition of the intrinsic apoptosis pathway. In addition, the expression of the autophagy markers LC3-II and beclin 1 was also increased in the IF group compared with ad libitum fed animals. In parallel, IF decreased the levels of the substrate protein of autophagy, p62, indicative of an upregulation of the autophagic processes. Treatment with 3-methyladenine (3-MA), a selective inhibitor of autophagy, reversed the downregulated apoptosis-related markers by IF. Finally, IF could activate the adenosine monophosphate (AMP)-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway and enhance lysosome function by upregulating transcription factor (TF)EB expression. Altogether, the present findings suggest that IF exerts a neuroprotective effect after acute SCI via the upregulation of autophagy, and further points to dietary interventions as a promising combinatorial treatment for SCI.

The role of resveratrol as a natural modulator in glia activation in experimental models of stroke

OBJECTIVE

Stroke is one of the most important causes of death and disability in modern and developing societies. In a stroke, both the glial cells and neurons develop apoptosis due to decreased cellular access to glucose and oxygen. Resveratrol (3, 5, 4'-trihydroxy-trans-stilbene) as a herbal compound shows neuroprotective and glioprotective effects. This article reviews how resveratrol can alleviate symptoms after stroke to help neurons to survive by modulating some signaling pathways in glia.

MATERIALS AND METHODS

Various databases such as ISI Web of Knowledge, Scopus, Medline, PubMed, and Google Scholar, were searched from 2000 to February 2020 to gather the required articles using appropriate keywords.

RESULTS

Resveratrol enhances anti-inflammatory and decreases inflammatory cytokines by affecting the signaling pathways in microglia such as AMP-activated protein kinase (5' adenosine monophosphate-activated protein kinase, AMPK), SIRT1 (sirtuin 1) and SOCS1 (suppressor of cytokine signaling 1). Furthermore, through miR-155 overexpressing in microglia, resveratrol promotes M2 phenotype polarization. Resveratrol also increases AMPK and inhibits GSK-3β (glycogen synthase kinase 3 beta) activity in astrocytes, which release energy, makes ATP available to neurons and reduces reactive oxygen species (ROS). Besides, resveratrol increases oligodendrocyte survival, which can lead to maintaining post-stroke brain homeostasis.

CONCLUSION

These results suggest that resveratrol can be considered a novel therapeutic agent for the reduction of stroke symptoms that can not only affect neuronal function but also play an important role in reducing neurotoxicity by altering glial activity and signaling.

Inhibiting HMGB1-RAGE axis prevents pro-inflammatory macrophages/microglia polarization and affords neuroprotection after spinal cord injury

Background

Spinal cord injury (SCI) favors a persistent pro-inflammatory macrophages/microglia-mediated response with only a transient appearance of anti-inflammatory phenotype of immune cells. However, the mechanisms controlling this special sterile inflammation after SCI are still not fully elucidated. It is known that damage-associated molecular patterns (DAMPs) released from necrotic cells after injury can trigger severe inflammation. High mobility group box 1(HMGB1), a ubiquitously expressed DNA binding protein, is an identified DAMP, and our previous study demonstrated that reactive astrocytes could undergo necroptosis and release HMGB1 after SCI in mice. The present study aimed to explore the effects and the possible mechanism of HMGB1on macrophages/microglia polarization, as well as the neuroprotective effects by HMGB1 inhibition after SCI.

Methods

In this study, the expression and the concentration of HMGB1 was determined by qRT-PCR, ELISA, and immunohistochemistry. Glycyrrhizin was applied to inhibit HMGB1, while FPS-ZM1 to suppress receptor for advanced glycation end products (RAGE). The polarization of macrophages/microglia in vitro and in vivo was detected by qRT-PCR, immunostaining, and western blot. The lesion area was detected by GFAP staining, while neuronal survival was examined by Nissl staining. Luxol fast blue (LFB) staining, DAB staining, and western blot were adopted to evaluate the myelin loss. Basso-Beattie-Bresnahan (BBB) scoring and rump-height Index (RHI) assay was applied to evaluate locomotor functional recovery.

Results

Our data showed that HMGB1 can be elevated and released from necroptotic astrocytes and HMGB1 could induce pro-inflammatory microglia through the RAGE-nuclear factor-kappa B (NF-κB) pathway. We further demonstrated that inhibiting HMGB1 or RAGE effectively decreased the numbers of detrimental pro-inflammatory macrophages/microglia while increased anti-inflammatory cells after SCI. Furthermore, our data showed that inhibiting HMGB1 or RAGE significantly decreased neuronal loss and demyelination, and improved functional recovery after SCI.

Conclusions

The data implicated that HMGB1-RAGE axis contributed to the dominant pro-inflammatory macrophages/microglia-mediated pro-inflammatory response, and inhibiting this pathway afforded neuroprotection for SCI. Thus, therapies designed to modulate immune microenvironment based on this cascade might be a prospective treatment for SCI.

The Beneficial Roles of SIRT1 in Neuroinflammation-Related Diseases

Sirtuins are the class III of histone deacetylases whose deacetylate of histones is dependent on nicotinamide adenine dinucleotide (NAD+). Among seven sirtuins, SIRT1 plays a critical role in modulating a wide range of physiological processes, including apoptosis, DNA repair, inflammatory response, metabolism, cancer, and stress. Neuroinflammation is associated with many neurological diseases, including ischemic stroke, bacterial infections, traumatic brain injury, Alzheimer's disease (AD), and Parkinson's disease (PD). Recently, numerous studies indicate the protective effects of SIRT1 in neuroinflammation-related diseases. Here, we review the latest progress regarding the anti-inflammatory and neuroprotective effects of SIRT1. First, we introduce the structure, catalytic mechanism, and functions of SIRT1. Next, we discuss the molecular mechanisms of SIRT1 in the regulation of neuroinflammation. Finally, we analyze the mechanisms and effects of SIRT1 in several common neuroinflammation-associated diseases, such as cerebral ischemia, traumatic brain injury, spinal cord injury, AD, and PD. Taken together, this information implies that SIRT1 may serve as a promising therapeutic target for the treatment of neuroinflammation-associated disorders.

Hydroxysafflor Yellow A Exerts Anti-Inflammatory Effects Mediated by SIRT1 in Lipopolysaccharide-Induced Microglia Activation

Abnormal microglia activation causes sever neuroinflammation, contributing to the development of many diseases, yet the mechanism remains incompletely unknown. In current study, we identified that Hydroxysafflor yellow A (HYA), a chalcone glycoside derived from Carthamus tinctorius L effectively attenuates LPS-induced inflammation response in primary microglia via regulating the expression of inflammatory genes and remodeling the polarization of microglia. We also reported the effects of HYA on improving lipopolysaccharide (LPS)-stimulated mitochondrial dysfunction and oxidative stress for the first time. Interestingly, we found that HYA could serves as an effective SIRT1 activator. Deficiency of SIRT1 abrogates the protective effects of HYA against LPS-induced response. Overall, our data suggest HYA, a novel SIRT1 activator, could serve as an effective approach to treat LPS-induced neurodegenerative diseases.

Pterostilbene Attenuates Cocultured BV-2 Microglial Inflammation-Mediated SH-SY5Y Neuronal Oxidative Injury via SIRT-1 Signalling

Microglial inflammation plays an important part in the progression of multiple neurological diseases, including neurodegenerative diseases, stroke, depression, and traumatic encephalopathy. Here, we aimed to explore the role of pterostilbene (PTE) in the microglial inflammatory response and subsequent damage of cocultured neural cells and partially explain the underlying mechanisms. In the coculture system of lipopolysaccharide-activated BV-2 microglia and SH-SY5Y neuroblastoma, PTE (only given to BV-2) exhibited protection on SH-SY5Y cells, evidenced by improved SH-SY5Y morphology and viability and LDH release. It also attenuated SH-SY5Y apoptosis and oxidative stress, evidenced by TUNEL and DCFH-DA staining, as well as MDA, SOD, and GSH levels. Moreover, PTE upregulated SIRT-1 expression and suppressed acetylation of NF-κB p65 subunit in BV-2 microglia, thus decreasing the inflammatory factors, including TNF-α and IL-6. Furthermore, the effects above were reversed by SIRT-1 inhibitor EX527. These results suggest that PTE reduces the microglia-mediated inflammatory response and alleviates subsequent neuronal apoptosis and oxidative injury via increasing SIRT-1 expression and inhibiting the NF-κB signalling pathway.

PARP1 Impedes SIRT1-Mediated Autophagy during Degeneration of the Retinal Pigment Epithelium under Oxidative Stress

The molecular mechanism underlying autophagy impairment in the retinal pigment epithelium (RPE) in dry age-related macular degeneration (AMD) is not yet clear. Based on the causative role of poly(ADP-ribose) polymerase 1 (PARP1) in RPE necrosis, this study examined whether PARP1 is involved in the autophagy impairment observed during dry AMD pathogenesis. We found that autophagy was downregulated following H2O2-induced PARP1 activation in ARPE-19 cells and olaparib, PARP1 inhibitor, preserved the autophagy process upon H2O2 exposure in ARPE-19 cells. These findings imply that PARP1 participates in the autophagy impairment upon oxidative stress in ARPE-19 cells. Furthermore, PARP1 inhibited autolysosome formation but did not affect autophagosome formation in H2O2-exposed ARPE-19 cells, demonstrating that PARP1 is responsible for impairment of late-stage autophagy in particular. Because PARP1 consumes NAD+ while exerting its catalytic activity, we investigated whether PARP1 impedes autophagy mediated by sirtuin1 (SIRT1), which uses NAD+ as its cofactor. A NAD+ precursor restored autophagy and protected mitochondria in ARPE-19 cells by preserving SIRT1 activity upon H2O2. Moreover, olaparib failed to restore autophagy in SIRT1-depleted ARPE-19 cells, indicating that PARP1 inhibits autophagy through SIRT1 inhibition. Next, we further examined whether PARP1-induced autophagy impairment occurs in the retinas of dry AMD model mice. Histological analyses revealed that olaparib treatment protected mouse retinas against sodium iodate (SI) insult, but not in retinas cotreated with SI and wortmannin, an autophagy inhibitor. Collectively, our data demonstrate that PARP1-dependent inhibition of SIRT1 activity impedes autophagic survival of RPE cells, leading to retinal degeneration during dry AMD pathogenesis.

Subventricular zone-derived extracellular vesicles promote functional recovery in rat model of spinal cord injury by inhibition of NLRP3 inflammasome complex formation

Spinal cord injury (SCI) is the destruction of spinal cord motor and sensory resulted from an attack on the spinal cord, which can cause significant physiological damage. The inflammasome is a multiprotein oligomer resulting in inflammation; the NLRP3 inflammasome composed of NLRP3, apoptosis-associated speck-like protein (ASC), procaspase-1, and cleavage of procaspase-1 into caspase-1 initiates the inflammatory response. Subventricular Zone (SVZ) is the origin of neural stem/progenitor cells (NS/PCs) in the adult brain. Extracellular vesicles (EVs) are tiny lipid membrane bilayer vesicles secreted by different types of cells playing an important role in cell-cell communications. The aim of this study was to investigate the effect of intrathecal transplantation of EVs on the NLRP3 inflammasome formation in SCI rats. Male wistar rats were divided into three groups as following: laminectotomy group, SCI group, and EVs group. EVs was isolated from SVZ, and characterized by western blot and DLS, and then injected into the SCI rats. Real-time PCR and western blot were carried out for gene expression and protein level of NLRP3, ASC, and Caspase-1. H&E and cresyl violet staining were performed for histological analyses, as well as BBB test for motor function. The results indicated high level in mRNA and protein level in SCI group in comparison with laminectomy (p < 0.001), and injection of EVs showed a significant reduction in the mRNA and protein levels in EVs group compared to SCI (p < 0.001). H&E and cresyl violet staining showed recovery in neural cells of spinal cord tissue in EVs group in comparison with SCI group. BBB test showed the promotion of motor function in EVs group compared to SCI in 14 days (p < 0.05). We concluded that the injection of EVs could recover the motor function in rats with SCI and rescue the neural cells of spinal cord tissue by suppressing the formation of the NLRP3 inflammasome complex.

Resveratrol decreases CD45+ CD206- subtype macrophages in LPS-induced murine acute lung injury by SOCS3 signalling pathway

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) are life-threatening condition in critically ill patients. Resveratrol (Res), a natural polyphenol, has therapeutic effect in animal model with ALI; however, whether Res attenuates ALI through modulation of macrophage phenotypes in the animal model remains unknown. We in this study treated LPS-induced murine ALI with 30 mg/kg Res and observed significantly reduced severity of ALI in the Res-treated mice 48 hours after Res treatment. Neutrophil infiltrates were significantly reduced, accompanied with lower infiltration of CD45⁺ Siglec F^- phenotype macrophages, but higher population of CD45⁺ Siglec F⁺ and CD45⁺ CD206⁺ alternatively activated macrophages (M2 cells) in the Res-treated mice with ALI. In addition, the expression of IL-1beta and CXCL15 cytokines was suppressed in the treated mice. However, Res treatment in mice with myeloid cell-restricted SOCS3 deficiency did not significantly attenuate ALI severity and failed to increase population of both CD45⁺ Siglec F⁺ and CD45⁺ CD206⁺ M2 subtype macrophages in the murine ALI. Further studies in wild-type macrophages revealed that Res treatment effectively reduced the expression of IL-6 and CXCL15, and increased the expression of arginase-1, SIRT1 and SOCS3. However, macrophages' lack of SOCS3 expression were resistant to the Res-induced suppression of IL-6 and CXCL15 in vitro. Thus, we conclude that Res suppressed CD45⁺ Siglec F^- and CD45⁺ CD206^- M1 subtype macrophages through SOCS3 signalling in the LPS-induced murine ALI.

The Role of Metabolic Remodeling in Macrophage Polarization and Its Effect on Skeletal Muscle Regeneration

Significance: Macrophages are crucial for tissue homeostasis. Based on their activation, they might display classical/M1 or alternative/M2 phenotypes. M1 macrophages produce pro-inflammatory cytokines, reactive oxygen species (ROS), and nitric oxide (NO). M2 macrophages upregulate arginase-1 and reduce NO and ROS levels; they also release anti-inflammatory cytokines, growth factors, and polyamines, thus promoting angiogenesis and tissue healing. Moreover, M1 and M2 display key metabolic differences; M1 polarization is characterized by an enhancement in glycolysis and in the pentose phosphate pathway (PPP) along with a decreased oxidative phosphorylation (OxPhos), whereas M2 are characterized by an efficient OxPhos and reduced PPP. Recent Advances: The glutamine-related metabolism has been discovered as crucial for M2 polarization. Vice versa, flux discontinuities in the Krebs cycle are considered additional M1 features; they lead to increased levels of immunoresponsive gene 1 and itaconic acid, to isocitrate dehydrogenase 1-downregulation and to succinate, citrate, and isocitrate over-expression. Critical Issues: A macrophage classification problem, particularly in vivo, originating from a gap in the knowledge of the several intermediate polarization statuses between the M1 and M2 extremes, characterizes this field. Moreover, the detailed features of metabolic reprogramming crucial for macrophage polarization are largely unknown; in particular, the role of β-oxidation is highly controversial. Future Directions: Manipulating the metabolism to redirect macrophage polarization might be useful in various pathologies, including an efficient skeletal muscle regeneration. Unraveling the complexity pertaining to metabolic signatures that are specific for the different macrophage subsets is crucial for identifying new compounds that are able to trigger macrophage polarization and that might be used for therapeutical purposes.

Hyperbaric oxygen improves functional recovery of rats after spinal cord injury via activating stromal cell-derived factor-1/CXC chemokine receptor 4 axis and promoting brain-derived neurothrophic factor expression

Background:

Spinal cord injury (SCI) is a worldwide medical concern. This study aimed to elucidate the mechanism underlying the protective effect of hyperbaric oxygen (HBO) against SCI-induced neurologic defects in rats via exploring the stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4) axis and expression of brain-derived neurotrophic factor (BDNF).

Methods:

An acute SCI rat model was established in Sprague-Dawley rats using the Allen method. Sixty rats were divided into four groups (n = 15 in each group): sham-operated, SCI, SCI treated with HBO (SCI + HBO), and SCI treated with both HBO and AMD3100 (an antagonist of CXCR4; SCI + HBO + AMD) groups. The rats were treated with HBO twice a day for 3 days and thereafter once a day after the surgery for up to 28 days. Following the surgery, neurologic assessments were performed with the Basso-Bettie-Bresnahan (BBB) scoring system on postoperative day (POD) 7, 14, 21, and 28. Spinal cord tissues were harvested to assess the expression of SDF-1, CXCR4, and BDNF at mRNA and protein levels, using quantitative real-time polymerase chain reaction, Western blot analysis, and histopathologic analysis.

Results:

HBO treatment recovered SCI-induced descent of BBB scores on POD 14, (1.25 ± 0.75 vs. 1.03 ± 0.66, P < 0.05), 21 (5.27 ± 0.89 vs. 2.56 ± 1.24, P < 0.05), and 28 (11.35 ± 0.56 vs. 4.23 ± 1.20, P < 0.05) compared with the SCI group. Significant differences were found in the mRNA levels of SDF-1 (mRNA: day 21, SCI + HBO vs. SCI + HBO + AMD, 2.89 ± 1.60 vs. 1.56 ± 0.98, P < 0.05), CXCR4 (mRNA: day 7, SCI + HBO vs. SCI, 2.99 ± 1.60 vs.1.31 ± 0.98, P < 0.05; day 14, SCI + HBO vs. SCI + HBO + AMD, 4.18 ± 1.60 vs. 0.80 ± 0.34, P < 0.05; day 21, SCI + HBO vs. SCI, 2.10 ± 1.01 vs.1.15 ± 0.03, P < 0.05), and BDNF (mRNA: day 7, SCI + HBO vs. SCI, 3.04 ± 0.41 vs. 2.75 ± 0.31, P < 0.05; day 14, SCI + HBO vs. SCI, 3.88 ± 1.59 vs. 1.11 ± 0.40, P < 0.05), indicating the involvement of SDF-1/CXCR4 axis in the protective effect of HBO.

Conclusions:

HBO might promote the recovery of neurologic function after SCI in rats via activating the SDF-1/CXCR4 axis and promoting BDNF expression.

Loureirin B Promotes Axon Regeneration by Inhibiting Endoplasmic Reticulum Stress: Induced Mitochondrial Dysfunction and Regulating the Akt/GSK-3β Pathway after Spinal Cord Injury

Axon retraction greatly limits functional recovery after spinal cord injury (SCI) and neuron polarization, which affects processes including axon formation and development, is a promising target for promoting axon regeneration. Increasing microtubule stability has been demonstrated to improve intrinsic axon regeneration processes and is critically related to endoplasmic reticulum (ER)-mitochondria interactions. We used real-time polymerase chain reaction, Western blotting, and immunofluorescence to screen a variety of natural compounds, and found that Loureirin B (LrB) effectively promoted neuron polarization and axon regeneration in vitro and in vivo. LrB significantly inhibited ER stress and thereby promoted mitochondrial functions by regulating mitochondrial fusion. Further, LrB reactivated the Akt/GSK-3β pathway, which plays critical roles in cell survival and microtubule stabilization. Taken together, our results suggest that the effects of LrB on neuron regeneration involve the inhibition of ER stress-induced mitochondrial dysfunction and activation of the Akt/GSK-3β pathway, which further promotes microtubule stabilization. LrB may therefore be a promising candidate for facilitating recovery following SCI.

Network-centric medicine for peripheral nerve injury: Treating the whole to boost endogenous mechanisms of neuroprotection and regeneration

Peripheral nerve injuries caused by accidents may lead to paralysis, sensory disturbances, anaesthesia, and lack of autonomic functions. Functional recovery after disconnection of the motoneuronal soma from target tissue with proximal rupture of axons is determined by several factors: motoneuronal soma viability, proper axonal sprouting across inhibitory zones and elongation toward specific muscle, effective synapse contact rebuilding, and prevention of muscle atrophy. Therapies, such as adjuvant drugs with pleiotropic effects, that promote functional recovery after peripheral nerve injury are needed. Toward this aim, we designed a drug discovery workflow based on a network-centric molecular vision using unbiased proteomic data and neural artificial computational tools. Our focus is on boosting intrinsic capabilities of neurons for neuroprotection; this is in contrast to the common approach based on suppression of a pathobiological pathway known to be associated with disease condition. Using our workflow, we discovered neuroheal, a combination of two repurposed drugs that promotes motoneuronal soma neuroprotection, is anti-inflammatory, enhances axonal regeneration after axotomy, and reduces muscle atrophy. This drug discovery workflow has thus yielded a therapy that is close to its clinical application.

Sirtuins in Neuroendocrine Regulation and Neurological Diseases

Silent information regulator 1 (SIRT1) is a mammalian homolog of the nicotinamide adenine dinucleotide (NAD)-dependent deacetylase sirtuin family. Sirtuin was originally studied as the lifespan-extending gene, silent information regulator 2 (SIRT2) in budding yeast. There are seven mammalian homologs of sirtuin (SIRT1–7), and SIRT1 is the closest homolog to SIRT2. SIRT1 modulates various key targets via deacetylation. In addition to histones, these targets include transcription factors, such as forkhead box O (FOXO), Ku70, p53, NF-κB, PPAR-gamma co-activator 1-alpha (PGC-1α), and peroxisome proliferator-activated receptor γ (PPARγ). SIRT1 has many biological functions, including aging, cell survival, differentiation, and metabolism. Genetic and physiological analyses in animal models have shown beneficial roles for SIRT1 in the brain during both development and adulthood. Evidence from in vivo and in vitro studies have revealed that SIRT1 regulates the cellular fate of neural progenitors, axon elongation, dendritic branching, synaptic plasticity, and endocrine function. In addition to its importance in physiological processes, SIRT1 has also been implicated in protection of neurons from degeneration in models of neurological diseases, such as traumatic brain injury and Alzheimer’s disease. In this review, we focus on the role of SIRT1 in the neuroendocrine system and neurodegenerative diseases. We also discuss the potential therapeutic implications of targeting the sirtuin pathway.

Sirt1 mediates improvement of isoflurane-induced memory impairment following hyperbaric oxygen preconditioning in middle-aged mice

Hyperbaric oxygen (HBO) preconditioning (PC) has been suggested as a feasible method to provide neuroprotection from postoperative cognitive dysfunction (POCD). However, whether HBO-PC can ameliorate cognitive deficits induced by isoflurane, and the possible mechanism by which it may exert its effect, has not yet been clarified. In the present study, middle-aged mice were exposed to isoflurane anesthesia (1.5 minimal alveolar concentration [MAC]) for 2 h to establish a POCD model. After HBO preconditioning, cognitive function and expression of hippocampal sirtuin 1 (Sirt1), nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase 1 (HO-1) were evaluated 24 h following isoflurane treatment, in the presence or absence of Sirt1 knockdown by short hairpin RNA (shRNA). HBO preconditioning increased the expression of Sirt1, Nrf2, and HO-1 and ameliorated memory dysfunction. Meanwhile, Sirt1 knockdown inhibited the expression of Nrf2 and HO-1 and attenuated the HBO preconditioning-associated memory improvement. Our results suggest that the application of HBO preconditioning is a useful treatment for POCD, and that Sirt1 may be a potential molecular target for POCD therapy.

Down-regulated miR-448 relieves spinal cord ischemia/reperfusion injury by up-regulating SIRT1

MicroRNAs play a crucial role in the progression of spinal cord ischemia/reperfusion injury (SCII). The role of miR-448 and SIRT1 in SCII was investigated in this study, to provide further insights into prevention and improvement of this disorder. In this study, expressions of miR-448 and SIRT1 protein were determined by qRT-PCR and western blot, respectively. Flow cytometry was used to analyze cell apoptosis. The endogenous expression of genes was modulated by recombinant plasmids and cell transfection. Dual-luciferase reporter assay was performed to determine the interaction between miR-448 and SIRT1. The Basso, Beattie, and Bresnahan score was used to measure the hind-limb function of rat. The spinal cord ischemia reperfusion injury model of adult rats was developed by abdominal aorta clamping, and the nerve function evaluation was completed by motor deficit index score. In SCII tissues and cells treated with hypoxia, miR-448 was up-regulated while SIRT1 was down-regulated. Hypoxia treatment reduced the expression of SIRT1 through up-regulating miR-448 in nerve cells. Up-regulation of miR-448 induced by hypoxia promoted apoptosis of nerve cells through down-regulating SIRT1. Down-regulated miR-448 improved neurological function and hind-limb motor function of rats with SCII by up-regulating SIRT1. Down-regulated miR-448 inhibited apoptosis of nerve cells and improved neurological function by up-regulating SIRT1, which contributes to relieving SCII.

Asiatic acid suppresses neuroinflammation in BV2 microgliaviamodulation of the Sirt1/NF-κB signaling pathway

Asiatic acid promotes Sirt1 expression and inhibits NF-κB-induced microglia activation.

Targeting the NLRP3 inflammasome to attenuate spinal cord injury in mice

BACKGROUND

Spinal cord injury (SCI) is a devastating disease, which results in tissue loss and neurologic dysfunction. NLRP3 inflammasome plays an important role in the mechanism of diverse diseases. However, no studies have demonstrated the role of NLRP3 inflammasome and the effects of NLRP3 inflammasome inhibitors in a mouse model of SCI. We investigated whether inhibition of NLRP3 inflammasome activation by the pharmacologic inhibitor BAY 11-7082 or A438079 could exert neuroprotective effects in a mouse model of SCI.

METHODS

SCI was performed using an aneurysm clip with a closing force of 30 g at the level of the T6-T7 vertebra for 1 min. Motor recovery was evaluated by an open-field test. Neuronal death was assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling and Nissl staining. Mitochondrial dysfunction was determined by quantitative real-time polymerase chain reaction (qPCR), western blot, and detection of mitochondrial membrane potential level. Microglia/macrophage activation and astrocytic response were evaluated by immunofluorescence labeling.

RESULTS

Inhibition of NLRP3 inflammasome activation by pharmacologic inhibitor BAY 11-7082 or A438079 reduced neuronal death, attenuated spinal cord anatomic damage, and promoted motor recovery. Furthermore, BAY 11-7082 or A438079 directly attenuated the levels of NLRP3 inflammasome and proinflammatory cytokines. Moreover, BAY 11-7082 or A438079 alleviated microglia/macrophage activation, neutrophils infiltration, and reactive gliosis, as well as mitochondrial dysfunction.

CONCLUSIONS

Collectively, our results demonstrate that pharmacologic suppression of NLRP3 inflammasome activation controls neuroinflammation, attenuates mitochondrial dysfunction, alleviates the severity of spinal cord damage, and improves neurological recovery after SCI. These data strongly indicate that the NLRP3 inflammasome is a vital contributor to the secondary damage of SCI in mice.