HMGB1 protein does not mediate the inflammatory response in spontaneous spinal cord regeneration: a hint for CNS regeneration

High mobility group box 1 in the central nervous system: regeneration hidden beneath inflammation

High-mobility group box 1 was first discovered in the calf thymus as a DNA-binding nuclear protein and has been widely studied in diverse fields, including neurology and neuroscience. High-mobility group box 1 in the extracellular space functions as a pro-inflammatory damage-associated molecular pattern, which has been proven to play an important role in a wide variety of central nervous system disorders such as ischemic stroke, Alzheimer's disease, frontotemporal dementia, Parkinson's disease, multiple sclerosis, epilepsy, and traumatic brain injury. Several drugs that inhibit high-mobility group box 1 as a damage-associated molecular pattern, such as glycyrrhizin, ethyl pyruvate, and neutralizing anti-high-mobility group box 1 antibodies, are commonly used to target high-mobility group box 1 activity in central nervous system disorders. Although it is commonly known for its detrimental inflammatory effect, high-mobility group box 1 has also been shown to have beneficial pro-regenerative roles in central nervous system disorders. In this narrative review, we provide a brief summary of the history of high-mobility group box 1 research and its characterization as a damage-associated molecular pattern, its downstream receptors, and intracellular signaling pathways, how high-mobility group box 1 exerts the repair-favoring roles in general and in the central nervous system, and clues on how to differentiate the pro-regenerative from the pro-inflammatory role. Research targeting high-mobility group box 1 in the central nervous system may benefit from differentiating between the two functions rather than overall suppression of high-mobility group box 1.

Sustainable inflammatory activation following spinal cord injury is driven by thrombin-mediated dynamic expression of astrocytic chemokines

Acute spinal cord injury (SCI) always results in sustainable recruitment of inflammatory cells driven by sequentially generated chemokines, thereby eliciting excessive neuroinflammation. However, the underlying mechanism of temporally produced chemokines remains elusive. Reactive astrocytes are known to be the main sources of chemokines at the lesion site, which can be immediately activated by thrombin following SCI. In the present study, SCI was shown to induce a sequential production of chemokines CCL2 and CCL5 from astrocytes, which were associated with a persistent infiltration of macrophages/microglia. The rapidly induced CCL2 and later induced CCL5 from astrocytes were regulated by thrombin at the damaged tissues. Investigation of the regulatory mechanism revealed that thrombin facilitated astrocytic CCL2 production through activation of ERK/JNK/NFκB pathway, whereas promoted CCL5 production through PLCβ3/NFκB and ERK/JNK/NFκB signal pathway. Inhibition of thrombin activity significantly decreased production of astrocytic CCL2 and CCL5, and reduced the accumulation of macrophages/microglia at the lesion site. Accordingly, the locomotor function of rats was remarkably improved. The present study has provided a new regulatory mechanism on thrombin-mediated sequential production of astrocytic chemokines, which might be beneficial for clinical therapy of CNS neuroinflammation.

Super-high procoagulant activity of gecko thrombin: A gift from sky dragon

AIMS

Gecko, the "sky dragon" named by Traditional Chinese Medicine, undergoes rapid coagulation and scarless regeneration following tail amputation in the natural ecology, providing a perfect opportunity to develop the efficient and safe drug for blood clotting. Here, gecko thrombin (gthrombin) was recombinantly prepared and comparatively studied on its procoagulant activity.

METHODS

The 3D structure of gthrombin was constructed using the homology modeling method of I-TASSER. The active gthrombin was prepared by the expression of gecko prethrombin-2 in 293 T cells, followed by purification with Ni2+ -chelating column chromatography prior to activation by snake venom-derived Ecarin. The enzymatic activities of gthrombin were assayed by hydrolysis of synthetic substrate S-2238 and the fibrinogen clotting. The vulnerable nerve cells were used to evaluate the toxicity of gthrombin at molecular and cellular levels.

RESULTS

The active recombinant gthrombin showed super-high catalytic and fibrinogenolytic efficiency than those of human under different temperatures and pH conditions. In addition, gthrombin made nontoxic effects on the central nerve cells including neurons, contrary to those of mammalian counterparts, which contribute to neuronal damage, astrogliosis, and demyelination.

CONCLUSIONS

A super-high activity but safe procoagulant candidate drug was identified from reptiles, which provided a promising perspective for clinical application in rapid blood clotting.

Thrombin induces morphological and inflammatory astrocytic responses via activation of PAR1 receptor

Spinal cord injury (SCI) will result in the significant elevation of thrombin production at lesion site via either breakage of blood-spinal cord barrier or upregulated expression within nerve cells. Thrombin-induced activation of the protease activated receptors (PARs) evokes various pathological effects that deteriorate the functional outcomes of the injured cord. The cellular consequences of thrombin action on the astrocytes, as well as the underlying mechanism are not fully elucidated by far. In the present study, SCI model of rats was established by contusion, and primary astrocytes were isolated for culture from newborn rats. The expression levels of thrombin and PAR1 receptor at lesion sites of the spinal cord were determined. The primary astrocytes cultured in vitro were stimulated with different concentration of thrombin, and the resultant morphological changes, inflammatory astrocytic responses, as well as PAR1-activated signal pathway of astrocytes were accordingly examined using various agonists or antagonists of the receptor. Thrombin was found to reverse astrocytic stellation, promote proliferation but inhibit migration of astrocytes. Furthermore, the serine protease was shown to facilitate inflammatory response of astrocytes through regulation of MAPKs/NFκB pathway. Our results have provided the morphological evidence of astrocytic reactivity in response to thrombin stimulation and its neuroinflammatory effects following SCI, which will be indicative for the fundamental insights of thrombin-induced neuropathology.

Self-Control of Inflammation during Tail Regeneration of Lizards

Lizards can spontaneously regenerate their lost tail without evoking excessive inflammation at the damaged site. In contrast, tissue/organ injury of its mammalian counterparts results in wound healing with a formation of a fibrotic scar due to uncontrolled activation of inflammatory responses. Unveiling the mechanism of self-limited inflammation occurring in the regeneration of a lizard tail will provide clues for a therapeutic alternative to tissue injury. The present review provides an overview of aspects of rapid wound healing and roles of antibacterial peptides, effects of leukocytes on the tail regeneration, self-blocking of the inflammatory activation in leukocytes, as well as inflammatory resistance of blastemal cells or immature somatic cells during lizard tail regeneration. These mechanistic insights of self-control of inflammation during lizard tail regeneration may lead in the future to the development of therapeutic strategies to fight injury-induced inflammation.

Adult astrocytes from reptiles are resistant to proinflammatory activation via sustaining Vav1 expression

Adult mammalian astrocytes are sensitive to inflammatory stimuli in the context of neuropathology or mechanical injury, thereby affecting functional outcomes of the central nervous system (CNS). In contrast, glial cells residing in the spinal cord of regenerative vertebrates exhibit a weak astroglial reaction similar to those of mammals in embryonic stages. Macrophage migration inhibitory factor (MIF) participates in multiple neurological disorders by activation of glial and immune cells. However, the mechanism of astrocytes from regenerative species, such as gecko astrocytes (gAS), in resistance to MIF-mediated inflammation in the severed cords remains unclear. Here, we compared neural stem cell markers among gAS, as well as adult (rAS) and embryonic (eAS) rat astrocytes. We observed that gAS retained an immature phenotype resembling rat eAS. Proinflammatory activation of gAS with gecko (gMIF) or rat (rMIF) recombinant protein was unable to induce the production of inflammatory cytokines, despite its interaction with membrane CD74 receptor. Using cross-species screening of inflammation-related mediators from models of gMIF- and rMIF-induced gAS and rAS, we identified Vav1 as a key regulator in suppressing the inflammatory activation of gAS. The gAS with Vav1 deficiency displayed significantly restored sensitivity to inflammatory stimuli. Meanwhile, gMIF acts to promote the migration of gAS through regulation of CXCL8 following cord lesion. Taken together, our results suggest that Vav1 contributes to the regulation of astrocyte-mediated inflammation, which might be beneficial for the therapeutic development of neurological diseases.

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.

Integrated Analysis of the Mechanisms of Da-Chai-Hu Decoction in Type 2 Diabetes Mellitus by a Network Pharmacology Approach

Background

The incidence of type 2 diabetes mellitus (T2DM) has increased year by year, which not only seriously affects people's quality of life, but also imposes a heavy economic burden on the family, society, and country. Currently, the pathogenesis, diagnosis, and treatment of T2DM are still unclear. Therefore, exploration of a precise multitarget treatment strategy is urgent. Here, we attempt to screen out the active components, effective targets, and functional pathways of therapeutic drugs through network pharmacology with taking advantages of traditional Chinese medicine (TCM) formulas for multitarget holistic treatment of diseases to clarify the potential therapeutic mechanism of TCM formulas and provide a systematic and clear thought for T2DM treatment.

Methods

First, we screened the active components of Da-Chai-Hu Decoction (DCHD) by absorption, distribution, metabolism, excretion, and toxicity (ADME/T) calculation. Second, we predicted and screened the active components of DCHD and its therapeutic targets for T2DM relying on the Traditional Chinese Medicine Systems Pharmacology Analysis Platform (TCMSP database) and Text Mining Tool (GoPubMed database), while using the Database for Annotation, Visualization, and Integrated Discovery (DAVID) to obtain T2DM targets. Third, we constructed a network of the active component-target, target-pathway of DCHD using Cytoscape software (http://cytoscape.org/,ver.3.5.1) and then analyzed gene function, related biological processes, and signal pathways through the DAVID database.

Results

We screened 77 active components from 1278 DCHD components and 116 effective targets from 253 ones. After matching the targets of T2DM, we obtained 38 important targets and 7 core targets were selected through further analysis. Through enrichment analysis, we found that these important targets were mainly involved in many biological processes such as oxidative stress, inflammatory reaction, and apoptosis. After analyzing the relevant pathways, the synthetic pathway for the treatment of T2DM was obtained, which provided a diagnosis-treatment idea for DCHD in the treatment of T2DM.

Conclusions

This article reveals the mechanism of DCHD in the treatment of T2DM related to inflammatory response and apoptosis through network pharmacology, which lays a foundation for further elucidation of drugs effective targets.

SOCS3 Attenuates GM-CSF/IFN-γ-Mediated Inflammation During Spontaneous Spinal Cord Regeneration

SOCS3, a feedback inhibitor of the JAK/STAT signal pathway, negatively regulates axonal regrowth and inflammation in the central nervous system (CNS). Here, we demonstrated a distinct role of SOCS3 in the injured spinal cord of the gecko following tail amputation. Severing the gecko spinal cord did not evoke an inflammatory cascade except for an injury-stimulated elevation of the granulocyte/macrophage colony-stimulating factor (GM-CSF) and interferon gamma (IFN-γ) cytokines. Simultaneously, the expression of SOCS3 was upregulated in microglia, and unexpectedly not in neurons. Enforced expression of SOCS3 was sufficient to suppress the GM-CSF/IFN-γ-driven inflammatory responses through its KIR domain by attenuating the activities of JAK1 and JAK2. SOCS3 was also linked to GM-CSF/IFN-γ-induced cross-tolerance. Transfection of adenovirus overexpressing SOCS3 in the injured cord resulted in a significant decrease of inflammatory cytokines. These results reveal a distinct role of SOCS3 in the regenerating spinal cord, and provide new hints for CNS repair in mammals.

Investigating the efficacy of UVSE protein at repairing CPD and 6-4 pp DNA damages in human cells

UV exposure could induce carcinogenic mutation in human cells, including CPD (Cyclobutane pyrimidine dimer), and 6-4 pp (6-4 photoproduct) DNA damages. Spiting the active BER (Base Excision Repair) system of human cells, it lacks initiator glycosylase, rendering these damages to be only repaired through NER (Nucleotide Excision Repair) system. Some microorganisms such as Deinococcus radiodurans bacteria have a BER system for repairing these damages with an enzyme coded by the uvsE gene. This study evaluated the efficacy of the recombinant UVSE protein for repairing the CPD and 6-4 pp DNA damages in human cells. At the current study, the optimized sequence of the uvsE gene was synthesized and expressed in Hek293T cell line. The identity of protein was ascertained through ELISA assay and the stability of expression was measured via qPCR. The human Hek293T cells with the recombinant protein and without it were exposed to the UV light, and the repair of DNA damages was analyzed in both conditions using CPD and 6-4PP ELISA Combo Kit. The results indicated that uvsE gene was successfully colonized and expressed and expression showed to be stable. Hek293T cells with recombinant uvsE gene showed efficacy at repairing 80% of CPD and 85% of 6-4 photoproducts during one hour, and more than 95% of damages over 4 h' repair time. Considering the outcome of this study, it could be concluded that the uvsE recombinant product is highly effective at repairing both CPD and 6-4 pp damages and could be considered as a preventive agent for UV-induced skin cancers.

Macrophage migration inhibitory factor derived from spinal cord is involved in activation of macrophages following gecko tail amputation

Macrophages and their initiation of acute inflammation have been defined to be functionally important in tissue repair and regeneration. In injury-induced production of macrophage migration inhibitory factor (MIF), which has been described as a pleiotropic protein that participates in multiple cellular and biologic processes, it is unknown whether it is involved in the regulation of macrophage events during the epimorphic regeneration. In the model of gecko tail amputation, the protein levels of gecko MIF (gMIF) have been determined to be significantly increased in the nerve cells of the spinal cord in association with the recruitment of macrophages to the lesion site. gMIF has been shown to interact with the CD74 receptor to promote the migration of macrophages through activation of Ras homolog gene family member A and to trigger inflammatory responses through MAPK signaling pathways. The determination of microsphere phagocytosis also indicated that gMIF could enhance macrophage phagocytosis. gMIF-mediated recruitment and activation of macrophages have been found to be necessary for gecko tail regeneration, as evidenced by the depletion of macrophages using clodronate liposomes. The results present a novel function of MIF during the epimorphic regeneration, which is beneficial for insights into its pleiotropic property.-Wang, Y., Wei, S., Song, H., Zhang, X., Wang, W., Du, N., Song, T., Liang, H., Chen, X., Wang, Y. Macrophage migration inhibitory factor derived from spinal cord is involved in activation of macrophages following gecko tail amputation.

PGE2 facilitates tail regeneration via activation of Wnt signaling in Gekko japonicus

Tail regeneration is a distinguishing feature of lizards; however, the mechanisms underlying tail regeneration remain elusive. Prostaglandin E2 (PGE2) is an arachidonic acid metabolite that has been extensively investigated in the inflammatory response under both physiological and pathological conditions. PGE2 also act as a regulator of hematopoietic stem cell homeostasis by interacting with Wnt signaling molecules. The present study aims to identify the effects of PGE2 on tail regeneration and the molecular mechanisms behind it. We initially found that PGE2 levels increased during the early stages of tail regeneration, accompanied by the up-regulated expression of cyclooxygenase 1 and cyclooxygenase 2. Next, we demonstrated that reduced PGE2 production leads to the retardation of tail regeneration. Subsequent experiments demonstrated that this effect is likely mediated by Wnt signaling, which proposing that the activation of the Wnt pathway is essential for the initiation of regeneration. The results showed that inhibition of PGE2 production could suppress Wnt activation and inhibit the proliferation of both epithelial and blastema cells. Furthermore, our findings indicated that forced activation of Wnt signaling could rescue the inhibitory effect of Cox antagonist on regeneration, suggesting a positive role of PGE2 on tail regeneration via a non-inflammatory mechanism.

Proteomics analysis of Schwann cell-derived exosomes: a novel therapeutic strategy for central nervous system injury

Exosomes are nanometer-sized vesicles involved in intercellular communication, and they are released by various cell types. To learn about exosomes produced by Schwann cells (SCs) and to explore their potential function in repairing the central nervous system (CNS), we isolated exosomes from supernatants of SCs by ultracentrifugation, characterized them by electron microscopy and immunoblotting and determined their protein profile using proteomic analysis. The results demonstrated that Schwann cell-derived exosomes (SCDEs) were, on average, 106.5 nm in diameter, round, and had cup-like concavity and expressed exosome markers CD9 and Alix but not tumor susceptibility gene (TSG) 101. We identified a total of 433 proteins, among which 398 proteins overlapped with the ExoCarta database. According to their specific functions, we identified 12 proteins that are closely related to CNS repair and classified them by different potential mechanisms, such as axon regeneration and inflammation inhibition. Gene Oncology analysis indicated that SCDEs are mainly involved in signal transduction and cell communication. Biological pathway analysis showed that pathways are mostly involved in exosome biogenesis, formation, uptake and axon regeneration. Among the pathways, the neurotrophin, PI3K-Akt and cAMP signaling pathways played important roles in CNS repair. Our study isolated SCDEs, unveiled their contents, presented potential neurorestorative proteins and pathways and provided a rich proteomics data resource that will be valuable for future studies of the functions of individual proteins in neurodegenerative diseases.

Blockade of receptor for advanced glycation end products promotes oligodendrocyte autophagy in spinal cord injury

Receptor for advanced glycation end product (RAGE) is involved in neuronal inflammation, cell cycle and differentiation. However, the role of RAGE in autophagy in the process of spinal cord injury (SCI) is yet unknown. The present study investigated the effect of RAGE blockade on autophagy in SCI. A rat Allen SCI model was established and the animals were micro-injected with rabbit RAGE neutralizing antibody or rabbit polyclonal Ig G immediately after the injury. The oligodendrocytes(OLs) marker, 2', 3'-cyclic nucleotide 3'-phosphodiesterase(CNPase) and autophagy-related marker microtubule associated protein light chain 3B(LC3B) were evaluated by Western blot. Furthermore, myelin basic protein (MBP) and LC3B double staining were observed in the SCI via immunofluorescence. The results showed that RAGE blockade reduced the expression of CNPase, promoted LC3B-II/I and p62 expression after SCI. In addition, the MBP/LC3B double positive oligodendrocytes-expressing LC3B was up-regulated by RAGE blockade. Moreover, RAGE blockade attenuated the neuronal survival at ventral horn after SCI. The present study revealed the role of RAGE in maintaining oligodendrocyte autophagy to promote neuronal regeneration post-SCI.

High mobility group box-1 (HMGB1) is increased in injured mouse spinal cord and can elicit neurotoxic inflammation

Inflammation is a ubiquitous but poorly understood consequence of spinal cord injury (SCI). The mechanisms controlling this response are unclear but culminate in the sequential activation of resident and recruited immune cells. Collectively, these cells can exert divergent effects on cell survival and tissue repair. HMGB1 is a ubiquitously expressed DNA binding protein and also a potent inflammatory stimulus. Necrotic cells release HGMB1, but HMGB1 also is actively secreted by inflammatory macrophages. A goal of this study was to quantify spatio-temporal patterns of cellular HMGB1 expression in a controlled mouse model of experimental SCI then determine the effects of HMGB1 on post-SCI neuroinflammation and recovery of function. We documented SCI-induced changes in nuclear and cytoplasmic distribution of HMGB1 in various cell types after SCI. The data reveal a time-dependent increase in HMGB1 mRNA and protein with protein reaching maximal levels 24-72 h post-injury then declining toward baseline 14-28 days post-SCI. Although most cells expressed nuclear HMGB1, reduced nuclear labeling with increased cytoplasmic expression was found in a subset of CNS macrophages suggesting that those cells begin to secrete HMGB1 at the injury site. In vitro data indicate that extracelluar HMGB1 helps promote the development of macrophages with a neurotoxic phenotype. The ability of HMGB1 to elicit neurotoxic macrophage functions was confirmed in vivo; 72 h after injecting 500 ng of recombinant HMGB1 into intact spinal cord ventral horn, inflammatory CNS macrophages co-localized with focal areas of neuronal killing. However, attempts to confer neuroprotection after SCI by blocking HMGB1 with a neutralizing antibody were unsuccessful. Collectively, these data implicate HMGB1 as a novel regulator of post-SCI inflammation and suggest that inhibition of HMGB1 could be a novel therapeutic target after SCI. Future studies will need to identify better methods to deliver optimal concentrations of HMGB1 antagonists to the injured spinal cord.

The role of HMGB1 in neuroinflammation and tissue repair: A potential therapeutic target for depression?

High mobility group protein box 1 (HMGB1), a sophisticated danger signal with pleiotropic functions, has been proved to function as a pro-inflammatory cytokine. In the central neural system (CNS), HMGB1 can stimulate microglia, the immune cell in the CNS, to release inflammatory factors and to cause chronic neurodegeneration. The evidence showed that HMGB1 can act as a pro-inflammatory cytokine mainly through its receptors like advanced glycation end product (RAGE), Toll-like 4 (TLR4), and so on. Moreover, HMGB1 contributed to the priming effects of stress-pretreatment and played a key role in neurodegeneration diseases via mediating neuroinflammation. However, the evidence also showed that HMGB1 played a role in tissue repair, with the ability to promote cell migration and proliferation, to induce the differentiation of mesenchymal stem cells (MSCs), and to regenerate spinal cord. These pleiotropic functions of HMGB1 make it possible to play a role from cell death to new life. Depression is a chronic, severe, and often life-threatening disease accompanied with impaired neurogenesis. The evidence showed that neuroinflammation played a key role in the process of depression. Depressive patients often showed a high expression of inflammatory cytokines in the blood and an activation of microglia in the brain. Meanwhile, they also showed a neuron deficit in the brain. Though they lack direct evidence linking HMGB1 with depression, the ability of HMGB1 that can function from neuroinflammation to tissue repair makes HMGB1 a promising therapeutic target of depression.

Receptor for Advanced Glycation End-Products (RAGE) Blockade Do Damage to Neuronal Survival via Disrupting Wnt/β-Catenin Signaling in Spinal Cord Injury

Wnt signaling are recognized key factors in neuronal development, cell proliferation and axonal guidance. However, RAGE effect on wnt signaling after spinal cord injury (SCI) are poorly understood. Our study aims to explore RAGE blockade effect on wnt signaling after SCI. We constructed Allen SCI model and micro-injected with RAGE neutralizing antibody or IgG after injury. We determined β-catenin, wnt3a and its receptor frizzled-5 via Western blot. We determined β-catenin/NeuN expression at 2 weeks after SCI via immunofluorescence (IF). We found that β-catenin, wnt3a and wnt receptor frizzled5 expression were activated after SCI at 3 days after injury. However, RAGE blockade inhibit β-catenin, wnt3a and frizzled5 expression. We found that β-catenin accumulation in NeuN cells were activated after SCI via IF, however, RAGE blockade reduced β-catenin and NeuN positive cells. RAGE blockade attenuated number of survived neurons and decreased area of spared white matter around the epicenter. RAGE signaling may involved in disrupting wnt signaling to aids neuronal recovery after SCI.

HMGB1 promotes ductular reaction and tumorigenesis in autophagy-deficient livers

Autophagy is important for liver homeostasis, and the deficiency leads to injury, inflammation, ductular reaction (DR), fibrosis, and tumorigenesis. It is not clear how these events are mechanistically linked to autophagy deficiency. Here, we reveal the role of high-mobility group box 1 (HMGB1) in two of these processes. First, HMGB1 was required for DR, which represents the expansion of hepatic progenitor cells (HPCs) implicated in liver repair and regeneration. DR caused by hepatotoxic diets (3,5-diethoxycarbonyl-1,4-dihydrocollidine [DDC] or choline-deficient, ethionine-supplemented [CDE]) also depended on HMGB1, indicating that HMGB1 may be generally required for DR in various injury scenarios. Second, HMGB1 promoted tumor progression in autophagy-deficient livers. Receptor for advanced glycation end product (RAGE), a receptor for HMGB1, was required in the same two processes and could mediate the proliferative effects of HMBG1 in isolated HPCs. HMGB1 was released from autophagy-deficient hepatocytes independently of cellular injury but depended on NRF2 and the inflammasome, which was activated by NRF2. Pharmacological or genetic activation of NRF2 alone, without disabling autophagy or causing injury, was sufficient to cause inflammasome-dependent HMGB1 release. In conclusion, HMGB1 release is a critical mechanism in hepatic pathogenesis under autophagy-deficient conditions and leads to HPC expansion as well as tumor progression.

HMGB1/Advanced Glycation End Products (RAGE) does not aggravate inflammation but promote endogenous neural stem cells differentiation in spinal cord injury

Receptor for advanced glycation end products (RAGE) signaling is involved in a series of cell functions after spinal cord injury (SCI). Our study aimed to elucidate the effects of RAGE signaling on the neuronal recovery after SCI. In vivo, rats were subjected to SCI with or without anti-RAGE antibodies micro-injected into the lesion epicenter. We detected Nestin/RAGE, SOX-2/RAGE and Nestin/MAP-2 after SCI by Western blot or immunofluorescence (IF). We found that neural stem cells (NSCs) co-expressed with RAGE were significantly activated after SCI, while stem cell markers Nestin and SOX-2 were reduced by RAGE blockade. We found that RAGE inhibition reduced nestin-positive NSCs expressing MAP-2, a mature neuron marker. RAGE blockade does not improve neurobehavior Basso, Beattie and Bresnahan (BBB) scores; however, it damaged survival of ventral neurons via Nissl staining. Through in vitro study, we found that recombinant HMGB1 administration does not lead to increased cytokines of TNF-α and IL-1β, while anti-RAGE treatment reduced cytokines of TNF-α and IL-1β induced by LPS via ELISA. Meanwhile, HMGB1 increased MAP-2 expression, which was blocked after anti-RAGE treatment. Hence, HMGB1/RAGE does not exacerbate neuronal inflammation but plays a role in promoting NSCs differentiating into mature neurons in the pathological process of SCI.

Autologous serum supplement favours in vitro regenerative paracrine factors synthesis

OBJECTIVES

Foetal bovine serum (FBS) is often the serum supplement of choice for in vitro human cell culture. This study compares the effect of FBS and autologous human serum (AuHS) supplement in human peripheral blood mononuclear cell (PBMC) culture to prepare secretome.

MATERIALS AND METHODS

The PBMC (n = 7) were cultured either in RPMI-1640 containing L-glutamine and 50 units/ml Penicillin-Streptomycin (BM) or in BM with either AuHS or FBS. Viability, proliferation and differentiation of PBMC were evaluated. Paracrine factors present in the secretomes (n = 6) were analysed using ProcartaPlex Human Cytokine panel (17 plex). Ingenuity Pathway Analysis (IPA) was performed to predict activation or inhibition of biological functions related to tissue regeneration.

RESULTS

The viability of PBMC that were cultured with FBS supplement was significantly reduced at 96 h compared to those at 0 and 24 h (P < .05). While the reduction of the viability of PBMC that were cultured with AuHS supplement was not significantly different compared to those at 0 and 24 h. The FBS secretomes prepared at 24 h was found to contain significantly higher amount of EGF (P < .05) compared to that in AuHS or BM secretome. The AuHS secretomes contained significantly higher amount of HGF at 24 (P < .05) and 96 h (P < .01), and VEGF-A at 24 h (P < .05) compared to those in the FBS secretomes. SDF-1 was not detected in the FBS secretomes prepared at either 24 or 96 hours. Double immunocytochemical staining revealed a marked increase in co-localization of SDF-1 and its receptor in PBMC that were cultured with AuHS supplement compared to that cultured with FBS supplement.

CONCLUSION

In secretome preparation, AuHS supplement favours synthesis of paracrine factors that are needed for regenerative therapy.

High-mobility group box-1 as an autocrine trophic factor in white matter stroke

Maintenance of white matter integrity in health and disease is critical for a variety of neural functions. Ischemic stroke in the white matter frequently results in degeneration of oligodendrocytes (OLs) and myelin. Previously, we found that toll-like receptor 2 (TLR2) expressed in OLs provides cell-autonomous protective effects on ischemic OL death and demyelination in white matter stroke. Here, we identified high-mobility group box-1 (HMGB1) as an endogenous TLR2 ligand that promotes survival of OLs under ischemic stress. HMGB1 rapidly accumulated in the culture medium of OLs exposed to oxygen-glucose deprivation (OGD). This conditioned medium exhibited a protective activity against ischemic OL death that was completely abolished by immunodepletion of HMGB1. Knockdown of HMGB1 or application of glycyrrhizin, a specific HMGB1 inhibitor, aggravated OGD-induced OL death, and recombinant HMGB1 application reduced the extent of OL death in a TLR2-dependent manner. We confirmed that cytosolic translocation of HMGB1 and activation of TLR2-mediated signaling pathways occurred in a focal white matter stroke model induced by endothelin-1 injection. Animals with glycyrrhizin coinjection showed an expansion of the demyelinating lesion in a TLR2-dependent manner, accompanied by aggravation of sensorimotor behavioral deficits. These results indicate that HMGB1/TLR2 activates an autocrine trophic signaling pathways in OLs and myelin to maintain structural and functional integrity of the white matter under ischemic conditions.

Potential Involvement of Snail Members in Neuronal Survival and Astrocytic Migration during the Gecko Spinal Cord Regeneration

Certain regenerative vertebrates such as fish, amphibians and reptiles are capable of regenerating spinal cord after injury. Most neurons of spinal cord will survive from the injury and regrow axons to repair circuits with an absence of glial scar formation. However, the underlying mechanisms of neuronal anti-apoptosis and glia-related responses have not been fully clarified during the regenerative process. Gecko has becoming an inspiring model to address spinal cord regeneration in amniotes. In the present study, we investigated the regulatory roles of Snail family members, the important transcriptional factors involved in both triggering of the cell migration and cell survival, during the spontaneous spinal cord regeneration. Both Snail1 and Snail3 have been shown to promote neuronal survival and astrocytic migration via anti-apoptotic and GTPases signaling following gecko tail amputation. Transforming growth factor-beta (TGFβ), together with other cytokines were involved in inducing expression of Snail protein. Our data indicate a conserved function of Snail proteins in embryonic development and tissue regeneration, which may provide clues for CNS repair in the mammals.

Reactive oxygen species generated from skeletal muscles are required for gecko tail regeneration

Reactive oxygen species (ROS) participate in various physiological and pathological functions following generation from different types of cells. Here we explore ROS functions on spontaneous tail regeneration using gecko model. ROS were mainly produced in the skeletal muscle after tail amputation, showing a temporal increase as the regeneration proceeded. Inhibition of the ROS production influenced the formation of autophagy in the skeletal muscles, and as a consequence, the length of the regenerating tail. Transcriptome analysis has shown that NADPH oxidase (NOX2) and the subunits (p40^phox and p47^phox) are involved in the ROS production. ROS promoted the formation of autophagy through regulation of both ULK and MAPK activities. Our results suggest that ROS produced by skeletal muscles are required for the successful gecko tail regeneration.

The HMGB1 signaling pathway activates the inflammatory response in Schwann cells

Schwann cells are not only myelinating cells, but also function as immune cells and express numerous innate pattern recognition receptors, including the Toll-like receptors. Injury to peripheral nerves activates an inflammatory response in Schwann cells. However, it is unclear whether specific endogenous damage-associated molecular pattern molecules are involved in the inflammatory response following nerve injury. In the present study, we demonstrate that a key damage-associated molecular pattern molecule, high mobility group box 1 (HMGB1), is upregulated following rat sciatic nerve axotomy, and we show colocalization of the protein with Schw-ann cells. HMGB1 alone could not enhance expression of Toll-like receptors or the receptor for advanced glycation end products (RAGE), but was able to facilitate migration of Schwann cells. When Schwann cells were treated with HMGB1 together with lipopolysaccharide, the expression levels of Toll-like receptors and RAGE, as well as inflammatory cytokines were upregulated. Our novel findings demonstrate that the HMGB1 pathway activates the inflammatory response in Schwann cells following peripheral nerve injury.

DAMPs from Cell Death to New Life

Our body handles tissue damage by activating the immune system in response to intracellular molecules released by injured tissues [damage-associated molecular patterns (DAMPs)], in a similar way as it detects molecular motifs conserved in pathogens (pathogen-associated molecular patterns). DAMPs are molecules that have a physiological role inside the cell, but acquire additional functions when they are exposed to the extracellular environment: they alert the body about danger, stimulate an inflammatory response, and finally promote the regeneration process. Beside their passive release by dead cells, some DAMPs can be secreted or exposed by living cells undergoing a life-threatening stress. DAMPs have been linked to inflammation and related disorders: hence, inhibition of DAMP-mediated inflammatory responses is a promising strategy to improve the clinical management of infection- and injury-elicited inflammatory diseases. However, it is important to consider that DAMPs are not only danger signals but also central players in tissue repair. Indeed, some DAMPs have been studied for their role in tissue healing after sterile or infection-associated inflammation. This review is focused on two exemplary DAMPs, HMGB1 and adenosine triphosphate, and their contribution to both inflammation and tissue repair.

CD59 mediates cartilage patterning during spontaneous tail regeneration

The regeneration-competent adult animals have ability to regenerate their lost complex appendages with a near-perfect replica, owing to the positional identity acquired by the progenitor cells in the blastema, i.e. the blastemal cells. CD59, a CD59/Ly6 family member, has been identified as a regulator of positional identity in the tail blastemal cells of Gekko japonicus. To determine whether this function of CD59 is unique to the regenerative amniote(s) and how CD59 mediates PD axis patterning during tail regeneration, we examined its protective role on the complement-mediated cell lysis and intervened CD59 expression in the tail blastemal cells using an in vivo model of adenovirus transfection. Our data revealed that gecko CD59 was able to inhibit complement-mediated cell lysis. Meanwhile, CD59 functioned on positional identity through expression in cartilage precursor cells. Intervening positional identity by overexpression or siRNA knockdown of CD59 resulted in abnormal cartilaginous cone patterning due to the decreased differentiation of blastemal cells to cartilage precursor cells. The cartilage formation-related genes were found to be under the regulation of CD59. These results indicate that CD59, an evolutionarily transitional molecule linking immune and regenerative regulation, affects tail regeneration by mediating cartilage patterning.

Dealing with Danger in the CNS: The Response of the Immune System to Injury

Fighting pathogens and maintaining tissue homeostasis are prerequisites for survival. Both of these functions are upheld by the immune system, though the latter is often overlooked in the context of the CNS. The mere presence of immune cells in the CNS was long considered a hallmark of pathology, but this view has been recently challenged by studies demonstrating that immunological signaling can confer pivotal neuroprotective effects on the injured CNS. In this review, we describe the temporal sequence of immunological events that follow CNS injury. Beginning with immediate changes at the injury site, including death of neural cells and release of damage-associated molecular patterns (DAMPs), and progressing through innate and adaptive immune responses, we describe the cascade of inflammatory mediators and the implications of their post-injury effects. We conclude by proposing a revised interpretation of immune privilege in the brain, which takes beneficial neuro-immune communications into account.

Axonal amphoterin mRNA is regulated by translational control and enhances axon outgrowth

High mobility group (HMG) proteins concentrate in the nucleus, interacting with chromatin. Amphoterin is an HMG protein (HMGB1) that has been shown to have extranuclear functions and can be secreted from some cell types. Exogenous amphoterin can increase neurite growth, suggesting that the secreted protein may have growth promoting activities in neurons. Consistent with this, we show that depletion of amphoterin mRNA from cultured adult rat DRG neurons attenuates neurite outgrowth, pointing to autocrine or paracrine mechanisms for its growth-promoting effects. The mRNA encoding amphoterin localizes to axonal processes and we showed recently that its 3'-UTR is sufficient for axonal localization of heterologous transcripts (Donnelly et al., 2013). Here, we show that amphoterin mRNA is transported constitutively into axons of adult DRG neurons. A preconditioning nerve injury increases the levels of amphoterin protein in axons without a corresponding increase in amphoterin mRNA in the axons. A 60 nucleotide region of the amphoterin mRNA 3'-UTR is necessary and sufficient for its localization into axons of cultured sensory neurons. Amphoterin mRNA 3'-UTR is also sufficient for axonal localization in distal axons of DRG neurons in vivo. Overexpression of axonally targeted amphoterin mRNA increases axon outgrowth in cultured sensory neurons, but axon growth is not affected when the overexpressed mRNA is restricted to the cell body.