High-mobility group box 1 release and redox regulation accompany regeneration and remodeling of skeletal muscle

Loss of adenosine A3 receptors accelerates skeletal muscle regeneration in mice following cardiotoxin-induced injury

Skeletal muscle regeneration is a complex process orchestrated by multiple interacting steps. An increasing number of reports indicate that inflammatory responses play a central role in linking initial muscle injury responses to timely muscle regeneration following injury. The nucleoside adenosine has been known for a long time as an endogenously produced anti-inflammatory molecule that is generated in high amounts during tissue injury. It mediates its physiological effects via four types of adenosine receptors. From these, adenosine A3 receptors (A3Rs) are not expressed by the skeletal muscle but are present on the surface of various inflammatory cells. In the present paper, the effect of the loss of A3Rs was investigated on the regeneration of the tibialis anterior (TA) muscle in mice following cardiotoxin-induced injury. Here we report that regeneration of the skeletal muscle from A3R-/- mice is characterized by a stronger initial inflammatory response resulting in a larger number of transmigrating inflammatory cells to the injury site, faster clearance of cell debris, enhanced proliferation and faster differentiation of the satellite cells (the muscle stem cells), and increased fusion of the generated myoblasts. This leads to accelerated skeletal muscle tissue repair and the formation of larger myofibers. Though the infiltrating immune cells expressed A3Rs and showed an increased inflammatory profile in the injured A3R-/- muscles, bone marrow transplantation experiments revealed that the increased response of the tissue-resident cells to tissue injury is responsible for the observed phenomenon. Altogether our data indicate that A3Rs are negative regulators of injury-related regenerative inflammation and consequently also that of the muscle fiber growth in the TA muscle. Thus, inhibiting A3Rs might have a therapeutic value during skeletal muscle regeneration following injury.

Mitochondria transplant therapy improves regeneration and restoration of injured skeletal muscle

BACKGROUND

Injection of exogenous mitochondria has been shown to improve the ischaemia-damaged myocardium, but the effect of mitochondrial transplant therapy (MTT) to restore skeletal muscle mass and function has not been tested following neuromuscular injury. Therefore, we tested the hypothesis that MTT would improve the restoration of muscle function after injury.

METHODS

BaCl₂ was injected into the gastrocnemius muscle of one limb of 8-12-week-old C57BL/6 mice to induce damage without injury to the resident stem cells. The contralateral gastrocnemius muscle was injected with phosphate-buffered saline (PBS) and served as the non-injured intra-animal control. Mitochondria were isolated from donor mice. Donor mitochondria were suspended in PBS or PBS without mitochondria (sham treatment) and injected into the tail vein of BaCl₂ injured mice 24 h after the initial injury. Muscle repair was examined 7, 14 and 21 days after injury.

RESULTS

MTT did not increase systemic inflammation in mice. Muscle mass 7 days following injury was 21.9 ± 2.1% and 17.4 ± 1.9% lower (P < 0.05) in injured as compared with non-injured intra-animal control muscles in phosphate-buffered saline (PBS)- and MTT-treated animals, respectively. Maximal plantar flexor muscle force was significantly lower in injured as compared with uninjured muscles of PBS-treated (-43.4 ± 4.2%, P < 0.05) and MTT-treated mice (-47.7 ± 7.3%, P < 0.05), but the reduction in force was not different between the experimental groups. The percentage of collagen and other non-contractile tissue in histological muscle cross sections, was significantly greater in injured muscles of PBS-treated mice (33.2 ± 0.2%) compared with MTT-treated mice (26.5 ± 0.2%) 7 days after injury. Muscle wet weight and maximal muscle force from injured MTT-treated mice had recovered to control levels by 14 days after the injury. However, muscle mass and force had not improved in PBS-treated animals by 14 days after injury. The non-contractile composition of the gastrocnemius muscle tissue cross sections was not different between control, repaired PBS-treated and repaired MTT-treated mice 14 days after injury. By 21 days following injury, PBS-treated mice had fully restored gastrocnemius muscle mass of the injured muscle to that of the uninjured muscle, although maximal plantar flexion force was still 19.4 ± 3.7% (P < 0.05) lower in injured/repaired gastrocnemius as compared with uninjured intra-animal control muscles.

CONCLUSIONS

Our results suggest that systemic mitochondria delivery can enhance the rate of muscle regeneration and restoration of muscle function following injury.

HMGB1 Promotes In Vitro and In Vivo Skeletal Muscle Atrophy through an IL-18-Dependent Mechanism

Skeletal muscle atrophy occurs due to muscle wasting or reductions in protein associated with aging, injury, and inflammatory processes. High-mobility group box-1 (HMGB1) protein is passively released from necrotic cells and actively secreted by inflammatory cells, and is implicated in the pathogenesis of various inflammatory and immune diseases. HMGB1 is upregulated in muscle inflammation, and circulating levels of the proinflammatory cytokine interleukin-18 (IL-18) are upregulated in patients with sarcopenia, a muscle-wasting disease. We examined whether an association exists between HMGB1 and IL-18 signaling in skeletal muscle atrophy. HMGB1-induced increases of IL-18 levels enhanced the expression of muscle atrophy markers and inhibited myogenic marker expression in C2C12 and G7 myoblast cell lines. HMGB1-induced increases of IL-18 production in C2C12 cells involved the RAGE/p85/Akt/mTOR/c-Jun signaling pathway. HMGB1 short hairpin RNA (shRNA) treatment rescued the expression of muscle-specific differentiation markers in murine C2C12 myotubes and in mice with glycerol-induced muscle atrophy. HMGB1 and IL-18 signaling was suppressed in the mice after HMGB1 shRNA treatment. These findings suggest that the HMGB1/IL-18 axis is worth targeting for the treatment of skeletal muscle atrophy.

The mechanism of HMGB1 secretion and release

High mobility group box 1 (HMGB1) is a nonhistone nuclear protein that has multiple functions according to its subcellular location. In the nucleus, HMGB1 is a DNA chaperone that maintains the structure and function of chromosomes. In the cytoplasm, HMGB1 can promote autophagy by binding to BECN1 protein. After its active secretion or passive release, extracellular HMGB1 usually acts as a damage-associated molecular pattern (DAMP) molecule, regulating inflammation and immune responses through different receptors or direct uptake. The secretion and release of HMGB1 is fine-tuned by a variety of factors, including its posttranslational modification (e.g., acetylation, ADP-ribosylation, phosphorylation, and methylation) and the molecular machinery of cell death (e.g., apoptosis, pyroptosis, necroptosis, alkaliptosis, and ferroptosis). In this minireview, we introduce the basic structure and function of HMGB1 and focus on the regulatory mechanism of HMGB1 secretion and release. Understanding these topics may help us develop new HMGB1-targeted drugs for various conditions, especially inflammatory diseases and tissue damage.

A nuclear protein that gets released after cell death or is actively secreted by immune cells offers a promising therapeutic target for treating diseases linked to excessive inflammation. Daolin Tang from the University of Texas Southwestern Medical Center in Dallas, USA, and colleagues review how cellular stresses can trigger the accumulation of HMGB1, a type of alarm signal protein that promotes the recruitment and activation of inflammation-promoting immune cells. The researchers discuss various mechanisms that drive both passive and active release of HMGB1 into the space around cells. These processes, which include enzymatic modifications of the HMGB1 protein, cell–cell interactions and molecular pathways of cell death, could be targeted by drugs to lessen tissue damage and inflammatory disease caused by HMGB1-induced immune responses

TAM kinase signaling is indispensable for proper skeletal muscle regeneration in mice

Skeletal muscle regeneration following injury results from the proliferation and differentiation of myogenic stem cells, called satellite cells, located beneath the basal lamina of the muscle fibers. Infiltrating macrophages play an essential role in the process partly by clearing the necrotic cell debris, partly by producing cytokines that guide myogenesis. Infiltrating macrophages are at the beginning pro-inflammatory, but phagocytosis of dead cells induces a phenotypic change to become healing macrophages that regulate inflammation, myoblast fusion and growth, fibrosis, vascularization and return to homeostasis. The TAM receptor kinases Mer and Axl are known efferocytosis receptors in macrophages functioning in tolerogenic or inflammatory conditions, respectively. Here we investigated their involvement in the muscle regeneration process by studying the muscle repair following cardiotoxin-induced injury in Mer^-/- mice. We found that Axl was the only TAM kinase receptor expressed on the protein level by skeletal muscle and C2C12 myoblast cells, while Mer was the dominant TAM kinase receptor in the CD45⁺ cells, and its expression significantly increased during repair. Mer ablation did not affect the skeletal muscle weight or structure, but following injury it resulted in a delay in the clearance of necrotic muscle cell debris, in the healing phenotype conversion of macrophages and consequently in a significant delay in the full muscle regeneration. Administration of the TAM kinase inhibitor BMS-777607 to wild type mice mimicked the effect of Mer ablation on the muscle regeneration process, but in addition, it resulted in a long-persisting necrotic area. Finally, in vitro inhibition of TAM kinase signaling in C2C12 myoblasts resulted in decreased viability and in impaired myotube growth. Our work identifies Axl as a survival and growth receptor in the mouse myoblasts, and reveals the contribution of TAM kinase-mediated signaling to the skeletal muscle regeneration both in macrophages and in myoblasts.

Odontoblast cell death induces NLRP3 inflammasome-dependent sterile inflammation and regulates dental pulp cell migration, proliferation and differentiation

AIM

To investigate the ability of dead odontoblasts to initiate NLRP3 inflammasome-dependent sterile inflammation and to explore the effect on dental pulp cell (DPCs) migration, proliferation and odontogenic differentiation.

METHODS

Odontoblast-like cells were subjected to freezing-thawing cycles to produce odontoblast necrotic cell lysate (ONCL). DPCs were treated with ONCL to assess proliferation and migration. THP-1 differentiated macrophages stimulated with ONCL and live cell imaging and western blotting were used to assess NLRP3 inflammasome activation. Cytokines were measured with multiplex arrays and ELISA. qPCR, alkaline phosphatase and Alizarin red assays were used to assess odontogenic differentiation of DPCs. Data were analysed using the t-test or anova followed by a Bonferroni post hoc test with the level of significance set at P ≤ 0.05.

RESULTS

ONCL induced migration and proliferation of DPCs. Treatment of THP-1 macrophages with ONCL resulted in the release of the inflammatory cytokines IL-1β, IL-6, IL-8, TNFα, IFN-γ, CCL2 and angiogenic growth factors, angiogenin and angiopoietin. This inflammatory response was associated with activation of NFκB, p38MAPK and NLRP3 inflammasome. To confirm that ONCL induced inflammatory response is NLRP3 inflammasome-dependent, treatment with a caspase-1 inhibitor and a specific NLRP3 inhibitor significantly reduced IL-1β release in THP-1 macrophages (P = 0.01 and 0.001). Inflammasome activation product, IL-1β, induced odontogenic differentiation of DPCS as evident by the increase in odontogenic genes expression DMP-1, RUNX-2, DSPP and SPP, alkaline phosphatase activity and mineralization.

CONCLUSION

Dead odontoblasts induced NLRP3 inflammasome-dependent sterile inflammation and activated the migration, proliferation and differentiation of DPCs.

Expression of select mRNA in Thoroughbreds with catastrophic racing injuries

BACKGROUND

The ability to identify horses at risk for catastrophic injuries continues to be a pressing issue for the racing industry, especially given recent events in North America.

OBJECTIVES

Since most catastrophic injuries occur in areas of existing pathology and this pathology is likely to elicit an inflammatory response, it was hypothesised that analysis of messenger RNA (mRNA) expression would detect significant changes in select genes in horses at risk for a catastrophic injury.

STUDY DESIGN

Prospective cohort study.

METHODS

Five racing jurisdictions across the United States participated in this study. A total of 686 Tempus^® RNA Blood Tube samples were collected for mRNA analysis from 107 catastrophically injured horses, as well as from noninjured horses sampled either prerace (n = 374) or postrace (n = 205). A subset of horses (n = 37) were sampled both prerace and postrace for analysis of expression changes during the postrace period.

RESULTS

Of 21 genes analysed via RT-qPCR, the expression of 12 genes (ALOX5AP, CD14, IL-10, IL-1β, IL-6, IL-8, MMP1, PTGS2, TLR4, TNFα, TNFSF13B and VEGFA) changed significantly within 45 minutes after a race and were excluded. Of the remaining nine genes (BMP-2, IGF-1, IL1RN, MMP2, MMP9, Osteoprotegrin, RANKL, SAA1 and TGFβ), three genes (IGF-1, IL1RN and MMP2) were found to be significantly different between catastrophically injured and noninjured horses using multiple logistic regression modelling. Receiver operating characteristic analysis of models, which included mRNA expression, demonstrated sensitivities from 76%-82% (95% CI: 67%-93%) and specificities from 84%-88% (95% CI: 71%-94%) at the Youden Index.

MAIN LIMITATIONS

Samples were collected as soon as possible postinjury (within 30 minutes).

CONCLUSIONS

Analysis of mRNA expression of specific genes in the future may be considered as an economical, accessible and noninvasive means by which horses at risk for catastrophic injury can be identified.

The calmodulin redox sensor controls myogenesis

Muscle aging is accompanied by blunted muscle regeneration in response to injury and disuse. Oxidative stress likely underlies this diminished response, but muscle redox sensors that act in regeneration have not yet been characterized. Calmodulin contains multiple redox sensitive methionines whose oxidation alters the regulation of numerous cellular targets. We have used the CRISPR-Cas9 system to introduce a single amino acid substitution M109Q that mimics oxidation of methionine to methionine sulfoxide in one or both alleles of the CALM1 gene, one of three genes encoding the muscle regulatory protein calmodulin, in C2C12 mouse myoblasts. When signaled to undergo myogenesis, mutated myoblasts failed to differentiate into myotubes. Although early myogenic regulatory factors were present, cells with the CALM1 M109Q mutation in one or both alleles were unable to withdraw from the cell cycle and failed to express late myogenic factors. We have shown that a single oxidative modification to a redox-sensitive muscle regulatory protein can halt myogenesis, suggesting a molecular target for mitigating the impact of oxidative stress in age-related muscle degeneration.

Exploring the therapeutic promise of targeting HMGB1 in rheumatoid arthritis

High mobility group box-1 (HMGB1) protein is a diverse, single polypeptide moiety, present in mammalian eukaryotic cells. In response to stimuli, this nuclear protein is actively secreted in to the extracellular compartment or passively released by the necrotic cells, in order to mediate inflammatory responses, by forming complexes with IL-1α, IL-1β, LPS and other moieties, and binding to RAGE, TLR and other receptor ligands, initiating downstream, signaling processes. This molecule acts as a proinflammatory cytokine and contributes to the progression of diseases like, acute lung injury, autoimmune liver damage, graft rejection immune response and arthritis. Small concentrations of HMGB1 are released during apoptosis, which facilitates oxidative regulation on Cys106, and propagates immune inactivating tolerogenic signals in the body. The review portrays the role of HMGB1 in rheumatoid arthritis, evidently supported by pre-clinical and clinical investigations, demonstrating extensive HMGB1 expression in synovial tissue and fluid as well as serum, excessive expression of transduction receptor signaling molecules, bone remodeling and uncontrolled expression of bone destroying osteoclastogenesis, resulting in destruction of articular cartilage, bone deformation and synovial proliferation, alleviating the pathogenesis in RA disease. Moreover, the review highlights the therapeutic regime targeting HMGB1, facilitating inhibition of its actions and release into the extracellular compartment, to ameliorate the destructive events that prevail in rheumatoid arthritis.

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.

The Janus face of HMGB1 in heart disease: a necessary update

High mobility group box 1 (HMGB1) is a ubiquitous nuclear protein involved in transcription regulation, DNA replication and repair and nucleosome assembly. HMGB1 is passively released by necrotic tissues or actively secreted by stressed cells. Extracellular HMGB1 acts as a damage-associated molecular pattern (DAMPs) molecule and gives rise to several redox forms that by binding to different receptors and interactors promote a variety of cellular responses, including tissue inflammation or regeneration. Inhibition of extracellular HMGB1 in experimental models of myocardial ischemia/reperfusion injury, myocarditis, cardiomyopathies induced by mechanical stress, diabetes, bacterial infection or chemotherapeutic drugs reduces inflammation and is protective. In contrast, administration of HMGB1 after myocardial infarction induced by permanent coronary artery ligation ameliorates cardiac performance by promoting tissue regeneration. HMGB1 decreases contractility and induces hypertrophy and apoptosis in cardiomyocytes, stimulates cardiac fibroblast activities, and promotes cardiac stem cell proliferation and differentiation. Interestingly, maintenance of appropriate nuclear HMGB1 levels protects cardiomyocytes from apoptosis by preventing DNA oxidative stress, and mice with HMGB1cardiomyocyte-specific overexpression are partially protected from cardiac damage. Finally, higher levels of circulating HMGB1 are associated to human heart diseases. Hence, during cardiac injury, HMGB1 elicits both harmful and beneficial responses that may in part depend on the generation and stability of the diverse redox forms, whose specific functions in this context remain mostly unexplored. This review summarizes recent findings on HMGB1 biology and heart dysfunctions and discusses the therapeutic potential of modulating its expression, localization, and oxidative-dependent activities.

Towards frailty biomarkers: Candidates from genes and pathways regulated in aging and age-related diseases

OBJECTIVE

Use of the frailty index to measure an accumulation of deficits has been proven a valuable method for identifying elderly people at risk for increased vulnerability, disease, injury, and mortality. However, complementary molecular frailty biomarkers or ideally biomarker panels have not yet been identified. We conducted a systematic search to identify biomarker candidates for a frailty biomarker panel.

METHODS

Gene expression databases were searched (http://genomics.senescence.info/genes including GenAge, AnAge, LongevityMap, CellAge, DrugAge, Digital Aging Atlas) to identify genes regulated in aging, longevity, and age-related diseases with a focus on secreted factors or molecules detectable in body fluids as potential frailty biomarkers. Factors broadly expressed, related to several "hallmark of aging" pathways as well as used or predicted as biomarkers in other disease settings, particularly age-related pathologies, were identified. This set of biomarkers was further expanded according to the expertise and experience of the authors. In the next step, biomarkers were assigned to six "hallmark of aging" pathways, namely (1) inflammation, (2) mitochondria and apoptosis, (3) calcium homeostasis, (4) fibrosis, (5) NMJ (neuromuscular junction) and neurons, (6) cytoskeleton and hormones, or (7) other principles and an extensive literature search was performed for each candidate to explore their potential and priority as frailty biomarkers.

RESULTS

A total of 44 markers were evaluated in the seven categories listed above, and 19 were awarded a high priority score, 22 identified as medium priority and three were low priority. In each category high and medium priority markers were identified.

CONCLUSION

Biomarker panels for frailty would be of high value and better than single markers. Based on our search we would propose a core panel of frailty biomarkers consisting of (1) CXCL10 (C-X-C motif chemokine ligand 10), IL-6 (interleukin 6), CX3CL1 (C-X3-C motif chemokine ligand 1), (2) GDF15 (growth differentiation factor 15), FNDC5 (fibronectin type III domain containing 5), vimentin (VIM), (3) regucalcin (RGN/SMP30), calreticulin, (4) PLAU (plasminogen activator, urokinase), AGT (angiotensinogen), (5) BDNF (brain derived neurotrophic factor), progranulin (PGRN), (6) α-klotho (KL), FGF23 (fibroblast growth factor 23), FGF21, leptin (LEP), (7) miRNA (micro Ribonucleic acid) panel (to be further defined), AHCY (adenosylhomocysteinase) and KRT18 (keratin 18). An expanded panel would also include (1) pentraxin (PTX3), sVCAM/ICAM (soluble vascular cell adhesion molecule 1/Intercellular adhesion molecule 1), defensin α, (2) APP (amyloid beta precursor protein), LDH (lactate dehydrogenase), (3) S100B (S100 calcium binding protein B), (4) TGFβ (transforming growth factor beta), PAI-1 (plasminogen activator inhibitor 1), TGM2 (transglutaminase 2), (5) sRAGE (soluble receptor for advanced glycosylation end products), HMGB1 (high mobility group box 1), C3/C1Q (complement factor 3/1Q), ST2 (Interleukin 1 receptor like 1), agrin (AGRN), (6) IGF-1 (insulin-like growth factor 1), resistin (RETN), adiponectin (ADIPOQ), ghrelin (GHRL), growth hormone (GH), (7) microparticle panel (to be further defined), GpnmB (glycoprotein nonmetastatic melanoma protein B) and lactoferrin (LTF). We believe that these predicted panels need to be experimentally explored in animal models and frail cohorts in order to ascertain their diagnostic, prognostic and therapeutic potential.

Cellular mechanisms and signals that coordinate plasma membrane repair

Plasma membrane forms the barrier between the cytoplasm and the environment. Cells constantly and selectively transport molecules across their plasma membrane without disrupting it. Any disruption in the plasma membrane compromises its selective permeability and is lethal, if not rapidly repaired. There is a growing understanding of the organelles, proteins, lipids, and small molecules that help cells signal and efficiently coordinate plasma membrane repair. This review aims to summarize how these subcellular responses are coordinated and how cellular signals generated due to plasma membrane injury interact with each other to spatially and temporally coordinate repair. With the involvement of calcium and redox signaling in single cell and tissue repair, we will discuss how these and other related signals extend from single cell repair to tissue level repair. These signals link repair processes that are activated immediately after plasma membrane injury with longer term processes regulating repair and regeneration of the damaged tissue. We propose that investigating cell and tissue repair as part of a continuum of wound repair mechanisms would be of value in treating degenerative diseases.

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.

Macrophage-derived superoxide production and antioxidant response following skeletal muscle injury

Macrophages are key players of immunity that display different functions according to their activation states. In a regenerative context, pro-inflammatory macrophages (Ly6C^pos) are involved in the mounting of the inflammatory response whereas anti-inflammatory macrophages (Ly6C^neg) dampen the inflammation and promote tissue repair. Reactive oxygen species (ROS) production is a hallmark of tissue injury and of subsequent inflammation as described in a bacterial challenge context. However, whether macrophages produce ROS following a sterile tissue injury is uncertain. In this study, we used complementary in vitro, ex vivo and in vivo experiments in mouse to show that macrophages do not release ROS following a sterile injury in skeletal muscle. Furthermore, expression profiles of genes involved in the response to oxidative stress in Ly6C^pos and Ly6C^neg macrophage subsets did not indicate any antioxidant response in this context. Finally, in vivo, pharmacological antioxidant supplementation with N-Acetyl-cysteine (NAC) following skeletal muscle injury did not alter macrophage phenotype during skeletal muscle regeneration. Overall, these results indicate that following a sterile injury, macrophage-derived ROS release is not involved in the regulation of the inflammatory response in the regenerating skeletal muscle.

Redox Control of Skeletal Muscle Regeneration

Skeletal muscle shows high plasticity in response to external demand. Moreover, adult skeletal muscle is capable of complete regeneration after injury, due to the properties of muscle stem cells (MuSCs), the satellite cells, which follow a tightly regulated myogenic program to generate both new myofibers and new MuSCs for further needs. Although reactive oxygen species (ROS) and reactive nitrogen species (RNS) have long been associated with skeletal muscle physiology, their implication in the cell and molecular processes at work during muscle regeneration is more recent. This review focuses on redox regulation during skeletal muscle regeneration. An overview of the basics of ROS/RNS and antioxidant chemistry and biology occurring in skeletal muscle is first provided. Then, the comprehensive knowledge on redox regulation of MuSCs and their surrounding cell partners (macrophages, endothelial cells) during skeletal muscle regeneration is presented in normal muscle and in specific physiological (exercise-induced muscle damage, aging) and pathological (muscular dystrophies) contexts. Recent advances in the comprehension of these processes has led to the development of therapeutic assays using antioxidant supplementation, which result in inconsistent efficiency, underlying the need for new tools that are aimed at precisely deciphering and targeting ROS networks. This review should provide an overall insight of the redox regulation of skeletal muscle regeneration while highlighting the limits of the use of nonspecific antioxidants to improve muscle function. Antioxid. Redox Signal. 27, 276-310.

The receptor for advanced glycation end products impairs collateral formation in both diabetic and non-diabetic mice

Diabetics often have poor perfusion in their limbs as a result of peripheral artery disease and an impaired ability to generate collateral vessels. The receptor for advanced glycation end products (RAGE) is one protein that is thought to play a detrimental role in collateral development in diabetics due to increased levels of advanced glycation end products (AGE), one of its ligands, in diabetes. Thus, the aim of this study was to investigate the role of RAGE in both diabetic and non-diabetic settings in a model of collateral formation in mice. Streptozotocin was used to induce diabetes in both wild type and RAGE knockout mice. Increased levels of the AGE, N^ɛ-(carboxymethyl) lysine (CML), were confirmed via an ELISA. A hindlimb ischemia model, in which the femoral artery is ligated, was used to drive collateral growth and reperfusion was assessed using laser Doppler perfusion imaging and histological analysis of vessels in the muscle. Both of these measurements showed impaired collateral growth in diabetic compared with wild-type mice as well as improved collateral growth in both diabetic and non-diabetic RAGE knockout mice when compared their wild-type counterparts. Distance on a freely accessed running wheel, used as a measure of perfusion recovery, showed that wild-type diabetic mice had functionally impaired recovery compared with their wild-type counterparts. Immunohistochemistry and immunoblotting showed that HMGB-1 (high-mobility group box 1), another RAGE ligand, was increased in the ischemic leg compared with the non-ischemic leg in all mice. This increase in HMGB-1 may explain improvement in animals lacking RAGE and its subsequent signaling. In conclusion, this study shows that RAGE impairs collateral growth in a diabetic setting and also in a non-diabetic setting. This demonstrates the importance of RAGE and alternate RAGE ligands in the setting of collateral vessel growth.

The Repair of Skeletal Muscle Requires Iron Recycling through Macrophage Ferroportin

Macrophages recruited at the site of sterile muscle damage play an essential role in the regeneration of the tissue. In this article, we report that the selective disruption of macrophage ferroportin (Fpn) results in iron accumulation within muscle-infiltrating macrophages and jeopardizes muscle healing, prompting fat accumulation. Macrophages isolated from the tissue at early time points after injury express ferritin H, CD163, and hemeoxygenase-1, indicating that they can uptake heme and store iron. At later time points they upregulate Fpn expression, thus acquiring the ability to release the metal. Transferrin-mediated iron uptake by regenerating myofibers occurs independently of systemic iron homeostasis. The inhibition of macrophage iron export via the silencing of Fpn results in regenerating muscles with smaller myofibers and fat accumulation. These results highlight the existence of a local pathway of iron recycling that plays a nonredundant role in the myogenic differentiation of muscle precursors, limiting the adipose degeneration of the tissue.

Oxidant Mechanisms in Renal Injury and Disease

SIGNIFICANCE

A common link between all forms of acute and chronic kidney injuries, regardless of species, is enhanced generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) during injury/disease progression. While low levels of ROS and RNS are required for prosurvival signaling, cell proliferation and growth, and vasoreactivity regulation, an imbalance of ROS and RNS generation and elimination leads to inflammation, cell death, tissue damage, and disease/injury progression.

RECENT ADVANCES

Many aspects of renal oxidative stress still require investigation, including clarification of the mechanisms which prompt ROS/RNS generation and subsequent renal damage. However, we currently have a basic understanding of the major features of oxidative stress pathology and its link to kidney injury/disease, which this review summarizes.

CRITICAL ISSUES

The review summarizes the critical sources of oxidative stress in the kidney during injury/disease, including generation of ROS and RNS from mitochondria, NADPH oxidase, and inducible nitric oxide synthase. The review next summarizes the renal antioxidant systems that protect against oxidative stress, including superoxide dismutase and catalase, the glutathione and thioredoxin systems, and others. Next, we describe how oxidative stress affects kidney function and promotes damage in every nephron segment, including the renal vessels, glomeruli, and tubules.

FUTURE DIRECTIONS

Despite the limited success associated with the application of antioxidants for treatment of kidney injury/disease thus far, preventing the generation and accumulation of ROS and RNS provides an ideal target for potential therapeutic treatments. The review discusses the shortcomings of antioxidant treatments previously used and the potential promise of new ones. Antioxid. Redox Signal. 25, 119-146.

Disruption of a Regulatory Network Consisting of Neutrophils and Platelets Fosters Persisting Inflammation in Rheumatic Diseases

A network of cellular interactions that involve blood leukocytes and platelets maintains vessel homeostasis. It plays a critical role in the response to invading microbes by recruiting intravascular immunity and through the generation of neutrophil extracellular traps (NETs) and immunothrombosis. Moreover, it enables immune cells to respond to remote chemoattractants by crossing the endothelial barrier and reaching sites of infection. Once the network operating under physiological conditions is disrupted, the reciprocal activation of cells in the blood and the vessel walls determines the vascular remodeling via inflammatory signals delivered to stem/progenitor cells. A deregulated leukocyte/mural cell interaction is an early critical event in the natural history of systemic inflammation. Despite intense efforts, the signals that initiate and sustain the immune-mediated vessel injury, or those that enforce the often-prolonged phases of clinical quiescence in patients with vasculitis, have only been partially elucidated. Here, we discuss recent evidence that implicates the prototypic damage-associated molecular pattern/alarmin, the high mobility group box 1 (HMGB1) protein in systemic vasculitis and in the vascular inflammation associated with systemic sclerosis. HMGB1 could represent a player in the pathogenesis of rheumatic diseases and an attractive target for molecular interventions.

Vascular Remodelling and Mesenchymal Transition in Systemic Sclerosis

Fibrosis of the skin and of internal organs, autoimmunity, and vascular inflammation are hallmarks of Systemic Sclerosis (SSc). The injury and activation of endothelial cells, with hyperplasia of the intima and eventual obliteration of the vascular lumen, are early features of SSc. Reduced capillary blood flow coupled with deficient angiogenesis leads to chronic hypoxia and tissue ischemia, enforcing a positive feed-forward loop sustaining vascular remodelling, further exacerbated by extracellular matrix accumulation due to fibrosis. Despite numerous developments and a growing number of controlled clinical trials no treatment has been shown so far to alter SSc natural history, outlining the need of further investigation in the molecular pathways involved in the pathogenesis of the disease. We review some processes potentially involved in SSc vasculopathy, with attention to the possible effect of sustained vascular inflammation on the plasticity of vascular cells. Specifically we focus on mesenchymal transition, a key phenomenon in the cardiac and vascular development as well as in the remodelling of injured vessels. Recent work supports the role of transforming growth factor-beta, Wnt, and Notch signaling in these processes. Importantly, endothelial-mesenchymal transition may be reversible, possibly offering novel cues for treatment.

Cell death, clearance and immunity in the skeletal muscle

The skeletal muscle is an immunologically unique tissue. Leukocytes, virtually absent in physiological conditions, are quickly recruited into the tissue upon injury and persist during regeneration. Apoptosis, necrosis and autophagy coexist in the injured/regenerating muscles, including those of patients with neuromuscular disorders, such as inflammatory myopathies, dystrophies, metabolic and mitochondrial myopathies and drug-induced myopathies. Macrophages are able to alter their function in response to microenvironment conditions and as a consequence coordinate changes within the tissue from the early injury throughout regeneration and eventual healing, and regulate the activation and the function of stem cells. Early after injury, classically activated macrophages ('M1') dominate the picture. Alternatively activated M2 macrophages predominate during resolution phases and regulate the termination of the inflammatory responses. The dynamic M1/M2 transition is increasingly felt to be the key to the homeostasis of the muscle. Recognition and clearance of debris originating from damaged myofibers and from dying stem/progenitor cells, stromal cells and leukocytes are fundamental actions of macrophages. Clearance of apoptotic cells and M1/M2 transition are causally connected and represent limiting steps for muscle healing. The accumulation of apoptotic cells, which reflects their defective clearance, has been demonstrated in various tissues to prompt autoimmunity against intracellular autoantigens. In the muscle, in the presence of type I interferon, apoptotic myoblasts indeed cause the production of autoantibodies, lymphocyte infiltration and continuous cycles of muscle injury and regeneration, mimicking human inflammatory myopathies. The clearance of apoptotic cells thus modulates the homeostatic response of the skeletal muscle to injury. Conversely, defects in the process may have deleterious local effects, guiding maladaptive tissue remodeling with collagen and fat accumulation and promoting autoimmunity itself. There is strong promise for novel treatments based on new knowledge of cell death, clearance and immunity in the muscle.

The role of oxidative stress in skeletal muscle injury and regeneration: focus on antioxidant enzymes

Reactive oxygen species (ROS) are generated in skeletal muscle both during the rest and contractile activity. Myogenic cells are equipped with antioxidant enzymes, like superoxide dismutase, catalase, glutathione peroxidase, γ-glutamylcysteine synthetase and heme oxygenase-1. These enzymes not only neutralise excessive ROS, but also affect myogenic regeneration at several stages: influence post-injury inflammatory reaction, enhance viability and proliferation of muscle satellite cells and myoblasts and affect their differentiation. Finally, antioxidant enzymes regulate also processes accompanying muscle regeneration-induce angiogenesis and reduce fibrosis. Elevated ROS production was also observed in Duchenne muscular dystrophy (DMD), a disease characterised by degeneration of muscle tissue and therefore-increased rate of myogenic regeneration. Antioxidant enzymes are consequently considered as target for therapies counteracting dystrophic symptoms. In this review we present current knowledge regarding the role of oxidative stress and systems of enzymatic antioxidant defence in muscular regeneration after both acute injury and persistent muscular degeneration.

Chemokine interaction with synergy-inducing molecules: fine tuning modulation of cell trafficking

Review on synergistic activities induced by heterocomplexes formed with chemokines.

Directed migration and arrest of leukocytes during homeostasis, inflammation, and tumor development is mediated by the chemokine system, which governs leukocyte migration and activities. Although we understand well the effects of different chemokines one by one, much less was known about the potential consequences of the concomitant expression of multiple chemokines or of their interaction with inflammatory molecules on leukocyte migration and functions. In the past 10 yr, several studies revealed the existence of additional features of chemokines: they can antagonize chemokine receptors or synergize with other chemokines, also by forming heterocomplexes. Moreover, recent data show that not only chemokines but also the alarmin high-mobility group box 1 can for a complex with CXCL12, enhancing its potency on CXCR4. The molecular mechanism underlying the effect of the heterocomplex has been partially elucidated, whereas its structure is a matter of current investigations. The present review discusses the current knowledge and relevance of the functions of heterocomplexes formed between chemokines or between the chemokine CXCL12 and the alarmin high-mobility group box 1. These studies highlight the importance of taking into account, when approaching innovative therapies targeting the chemokine system, also the fact that some chemokines and molecules released in inflammation, can considerably affect the activity of chemokine receptor agonists.

The HMGB1-RAGE Inflammatory Pathway: Implications for Brain Injury-Induced Pulmonary Dysfunction

SIGNIFICANCE

Deceased patients who have suffered severe traumatic brain injury (TBI) are the largest source of organs for lung transplantation. However, due to severely compromised pulmonary lung function, only one-third of these patients are eligible organ donors, with far fewer capable of donating lungs (∼ 20%). As a result of this organ scarcity, understanding and controlling the pulmonary pathophysiology of potential donors are key to improving the health and long-term success of transplanted lungs.

RECENT ADVANCES

Although the exact mechanism by which TBI produces pulmonary pathophysiology remains unclear, it may be related to the release of damage-associated molecular patterns (DAMPs) from the injured tissue. These heterogeneous, endogenous host molecules can be rapidly released from damaged or dying cells and mediate sterile inflammation following trauma. In this review, we highlight the interaction of the DAMP, high-mobility group box protein 1 (HMGB1) with the receptor for advanced glycation end-products (RAGE), and toll-like receptor 4 (TLR4).

CRITICAL ISSUES

Recently published studies are reviewed, implicating the release of HMGB1 as producing marked changes in pulmonary inflammation and physiology following trauma, followed by an overview of the experimental evidence demonstrating the benefits of blocking the HMGB1-RAGE axis.

FUTURE DIRECTIONS

Targeting the HMGB1 signaling axis may increase the number of lungs available for transplantation and improve long-term benefits for organ recipient patient outcomes.

Primary glioblastoma multiforme tumors and recurrence : Comparative analysis of the danger signals HMGB1, HSP70, and calreticulin

PURPOSE

Glioblastoma multiforme (GBM) is the most common and aggressive brain tumor. Despite improved multimodal therapies, the tumor recurs in most cases. Diverging patient survival suggests great tumor heterogeneity and different therapy responses. Danger signals such as high-mobility group box protein 1 (HMGB1), heat shock protein 70 (HSP70), and calreticulin (CRT) are biomarker candidates, due to their association with tumor progression versus induction of antitumor immune responses. Overexpression of these danger signals has been reported for various types of tumors; however, their role in GBM is still elusive. A direct comparison of their expression in the primary tumor versus the corresponding relapse is still lacking for most tumor entities.

PATIENTS AND METHODS

We therefore performed an expression analysis by immunohistochemistry of the danger signals HMGB1, HSP70, and CRT in primary tumors and the corresponding relapses of 9 patients with de novo GBM.

RESULTS

HMGB1 was highly expressed in primary tumors with a significant reduction in the respective relapse. The extracellular HSP70 expression was significantly increased in the relapse compared to the primary tumor. CRT was generally highly expressed in the primary tumor, with a slight increase in the relapse.

CONCLUSION

The combination of a decreased expression of HMGB1, an increased expression of extracellular HSP70, and an increased expression of CRT in the relapse seems to be beneficial for patient survival. HMGB1, extracellular HSP70, and CRT could be taken into concerted consideration as potential biomarkers for the prognosis of patients with GBM.

Role of inflammatory cells in fibroblast activation

Although fibrosis is an essential response to acute cardiac tissue injury, prolonged myofibroblast activation and progressive fibrosis lead to further distortion of tissue architecture and worsened cardiac function. Thus, optimal tissue repair following injury requires tight control over myofibroblast activation. It is now recognized that inflammation plays a critical role in regulating fibrosis. In this review we will highlight how advances in the field of innate immunity have led to a better understanding of the role of inflammation in cardiovascular disease and, in particular, in the regulation of fibrosis. Specifically, we will discuss how the innate immune system recognizes tissue damage in settings of acute injury and chronic cardiovascular disease. We will also review the role of different cell populations in this response, particularly the unique role of different macrophage subsets and mast cells.

FOXP3+ T Cells Recruited to Sites of Sterile Skeletal Muscle Injury Regulate the Fate of Satellite Cells and Guide Effective Tissue Regeneration

Muscle injury induces a classical inflammatory response in which cells of the innate immune system rapidly invade the tissue. Macrophages are prominently involved in this response and required for proper healing, as they are known to be important for clearing cellular debris and supporting satellite cell differentiation. Here, we sought to assess the role of the adaptive immune system in muscle regeneration after acute damage. We show that T lymphocytes are transiently recruited into the muscle after damage and appear to exert a pro-myogenic effect on muscle repair. We observed a decrease in the cross-sectional area of regenerating myofibers after injury in Rag2^-/- γ-chain^-/- mice, as compared to WT controls, suggesting that T cell recruitment promotes muscle regeneration. Skeletal muscle infiltrating T lymphocytes were enriched in CD4⁺CD25⁺FOXP3⁺ cells. Direct exposure of muscle satellite cells to in vitro induced Treg cells effectively enhanced their expansion, and concurrently inhibited their myogenic differentiation. In vivo, the recruitment of Tregs to acutely injured muscle was limited to the time period of satellite expansion, with possibly important implications for situations in which inflammatory conditions persist, such as muscular dystrophies and inflammatory myopathies. We conclude that the adaptive immune system, in particular T regulatory cells, is critically involved in effective skeletal muscle regeneration. Thus, in addition to their well-established role as regulators of the immune/inflammatory response, T regulatory cells also regulate the activity of skeletal muscle precursor cells, and are instrumental for the proper regeneration of this tissue.

Necrotic myocardial cells release damage-associated molecular patterns that provoke fibroblast activation in vitro and trigger myocardial inflammation and fibrosis in vivo

BACKGROUND

Tissue injury triggers inflammatory responses that promote tissue fibrosis; however, the mechanisms that couple tissue injury, inflammation, and fibroblast activation are not known. Given that dying cells release proinflammatory "damage-associated molecular patterns" (DAMPs), we asked whether proteins released by necrotic myocardial cells (NMCs) were sufficient to activate fibroblasts in vitro by examining fibroblast activation after stimulation with proteins released by necrotic myocardial tissue, as well as in vivo by injecting proteins released by necrotic myocardial tissue into the hearts of mice and determining the extent of myocardial inflammation and fibrosis at 72 hours.

METHODS AND RESULTS

The freeze-thaw technique was used to induce myocardial necrosis in freshly excised mouse hearts. Supernatants from NMCs contained multiple DAMPs, including high mobility group box-1 (HMGB1), galectin-3, S100β, S100A8, S100A9, and interleukin-1α. NMCs provoked a significant increase in fibroblast proliferation, α-smooth muscle actin activation, and collagen 1A1 and 3A1 mRNA expression and significantly increased fibroblast motility in a cell-wounding assay in a Toll-like receptor 4 (TLR4)- and receptor for advanced glycation end products-dependent manner. NMC stimulation resulted in a significant 3- to 4-fold activation of Akt and Erk, whereas pretreatment with Akt (A6730) and Erk (U0126) inhibitors decreased NMC-induced fibroblast proliferation dose-dependently. The effects of NMCs on cell proliferation and collagen gene expression were mimicked by several recombinant DAMPs, including HMGB1 and galectin-3. Moreover, immunodepletion of HMGB1 in NMC supernatants abrogated NMC-induced cell proliferation. Finally, injection of NMC supernatants or recombinant HMGB1 into the heart provoked increased myocardial inflammation and fibrosis in wild-type mice but not in TLR4-deficient mice.

CONCLUSIONS

These studies constitute the initial demonstration that DAMPs released by NMCs induce fibroblast activation in vitro, as well as myocardial inflammation and fibrosis in vivo, at least in part, through TLR4-dependent signaling.

Modulation of radiochemoimmunotherapy-induced B16 melanoma cell death by the pan-caspase inhibitor zVAD-fmk induces anti-tumor immunity in a HMGB1-, nucleotide- and T-cell-dependent manner

One prerequisite that radiotherapy (RT) and chemotherapy (CT) result in anti-tumor immune responses is triggering of immunogenic cell death forms such as necroptosis. The latter is inducible by inhibition of apoptosis with the pan-caspase inhibitor zVAD-fmk. The design of multimodal therapies that overcome melanoma's resistance to apoptosis is a big challenge of oncoimmunology. As hints exist that immune stimulation by hyperthermia (HT) augments the efficacy of melanoma therapies and that tumors can be sensitized for RT with zVAD-fmk, we asked whether combinations of RT with dacarbazine (DTIC) and/or HT induce immunogenic melanoma cell death and how this is especially influenced by zVAD-fmk. Necroptosis was inducible in poorly immunogenic B16-F10 melanoma cells and zVAD-fmk generally increased melanoma cell necrosis concomitantly with the release of HMGB1. Supernatants (SNs) of melanoma cells whose cell death was modulated with zVAD-fmk induced an upregulation of the activation markers CD86 and MHCII on macrophages. The same was seen on dendritic cells (DCs), but only when zVAD-fmk was added to multimodal tumor treatments including DTIC. DCs of MyD88 KO mice and DCs incubated with SNs containing apyrase did not increase the expression of these activation markers on their surface. The in vivo experiments revealed that zVAD-fmk decreases the tumor growth significantly and results in a significantly reduced tumor infiltration of Tregs when added to multimodal treatment of the tumor with RT, DTIC and HT. Further, a significantly increased DC and CD8+ T-cell infiltration into the tumor and in the draining lymph nodes was induced, as well as an increased expression of IFNγ by CD8+ T cells. However, zVAD-fmk did not further reduce tumor growth in MyD88 KO mice, mice treated with apyrase or RAG KO mice. We conclude that HMGB1, nucleotides and CD8+ T cells mediate zVAD-fmk induced anti-melanoma immune reactions in multimodal therapy settings.

Required role of apoptotic myogenic precursors and toll-like receptor stimulation for the establishment of autoimmune myositis in experimental murine models

OBJECTIVE

Muscle regeneration is a hallmark of the idiopathic inflammatory myopathies (IIMs), a group of autoimmune disorders that are characterized by leukocyte infiltration and dysfunction of the skeletal muscle. Despite detailed studies describing the clinical and histopathologic features of IIMs, the immunopathogenesis of these disorders remains undefined. The aim of this study was to investigate the immunopathologic processes of autoimmune myositis in experimental murine models.

METHODS

Expression of the autoantigen histidyl-transfer RNA synthetase (HisRS) was analyzed in mice with acutely injured or dystrophic muscles, in inflammatory leukocytes, and in purified satellite cells. Anti-HisRS antibodies and myositis induction were assessed in mice after muscle injury and immunization with apoptotic satellite cells or C2C12 myoblasts, in the presence or absence of the Toll-like receptor 7 (TLR-7) agonist R848.

RESULTS

Muscle necrosis, leukocyte infiltration, and myofiber regeneration induced by toxic agents (cardiotoxin or glycerol) or promoted by genetic disruption of the α-sarcoglycan/dystrophin complex in mice were uniformly associated with up-regulated expression of HisRS. Although regenerating myofibers and purified satellite cells are known to show increased expression of HisRS in these settings, anti-HisRS antibodies were not detectable. However, intramuscular immunization with ultraviolet B-irradiated, HisRS-expressing apoptotic myoblasts in the presence of R848 triggered the production of anti-HisRS IgG antibodies as well as persistent lymphocyte infiltration and prolonged/delayed muscle regeneration. Conversely, intramuscular administration of R848 alone or in combination with living or postapoptotic/necrotic myoblasts failed to generate this myositis phenotype.

CONCLUSION

In the presence of TLR/adjuvant signals and underlying muscle injury, apoptotic myogenic precursors expressing high levels of autoantigen can provoke autoantibody formation and lymphocytic infiltration of muscle tissue, effectively replicating the features of IIM.

Decreased eccentric exercise-induced macrophage infiltration in skeletal muscle after supplementation with a class of ginseng-derived steroids

Dammarane steroids (DS) are a class of chemical compounds present in Panax ginseng. Here, we evaluated the effect of 10 weeks of DS supplementation on inflammatory modulation in the soleus muscle following eccentric exercise (EE)-induced muscle damage (downhill running). Eighty rats were randomized into 4 groups of DS supplementation (saline, 20, 60, 120 mg/kg body weight). Inflammatory markers were measured at rest and again 1 h after EE. At rest, NFκB signaling, TNF-alpha and IL-6 mRNAs, 3-nitrotyrosine, glutathione peroxidase, and GCS (glutamylcysteine synthetase) levels were significantly elevated in the skeletal muscle of DS-treated rats in a dose-dependent manner. Additionally, there were no detectable increases in the number of necrotic muscle fibers or CD68+ M1 macrophages. However, muscle strength, centronucleation, IL-10 mRNA expression, and the number of CD163+ M2 macrophages increased significantly over controls with DS treatment in rat soleus muscle. Under EE-challenged conditions, significant increases in muscle fiber necrosis, CD68+ M1 macrophage distribution, and 3-nitrotyrosine were absent in rats that received low and medium doses (20 and 60 mg/kg) of DS treatment, suggesting that DS possess anti-inflammatory action protecting against a muscle-damaging challenge. However, this protective activity was diminished when a high dose of DS (120 mg/kg) was administered, suggesting that DS possess hormetic properties. In conclusion, our study provides new evidence suggesting that DS is an ergogenic component of ginseng that potentiate inflammation at baseline but that produce anti-inflammatory effects on skeletal muscle following muscle-damaging exercise. Furthermore, high doses should be avoided in formulating ginseng-based products.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.

Identification of a functional interaction of HMGB1 with Receptor for Advanced Glycation End-products in a model of neuropathic pain

Recent studies indicate that the release of high mobility group box 1 (HMGB1) following nerve injury may play a central role in the pathogenesis of neuropathic pain. HMGB1 is known to influence cellular responses within the nervous system via two distinct receptor families; the Receptor for Advanced Glycation End-products (RAGE) and Toll-like receptors (TLRs). The degree to which HMGB1 activates a receptor is thought to be dependent upon the oxidative state of the ligand, resulting in the functional isoforms of all-thiol HMGB1 (at-HMGB1) acting through RAGE, and disufide HMGB1 (ds-HMGB1) interacting with TLR4. Though it is known that dorsal root ganglia (DRG) sensory neurons exposed to HMGB1 and TLR4 agonists can influence excitation, the degree to which at-HMGB1 signaling through neuronal RAGE contributes to neuropathic pain is unknown. Here we demonstrate that at-HMGB1 activation of nociceptive neurons is dependent on RAGE and not TLR4. To distinguish the possible role of RAGE on neuropathic pain, we characterized the changes in RAGE mRNA expression up to one month after tibial nerve injury (TNI). RAGE mRNA expression in lumbar dorsal root ganglion (DRG) is substantially increased by post-injury day (PID) 28 when compared with sham injured rodents. Protein expression at PID28 confirms this injury-induced event in the DRG. Moreover, a single exposure to monoclonal antibody to RAGE (RAGE Ab) failed to abrogate pain behavior at PID 7, 14 and 21. However, RAGE Ab administration produced reversal of mechanical hyperalgesia on PID28. Thus, at-HMGB1 activation through RAGE may be responsible for sensory neuron sensitization and mechanical hyperalgesia associated with chronic neuropathic pain states.

5-Fluorouracil causes leukocytes attraction in the peritoneal cavity by activating autophagy and HMGB1 release in colon carcinoma cells

Signals released by leukocytes contribute to tumor growth and influence the efficacy of antineoplastic treatments. The outcome of peritoneal carcinomatosis treatments is unsatisfactory, possibly because chemotherapy activates events that have in the long-term deleterious effects. In this study we offer evidence that 5-fluorouracile (5-FU), besides provoking apoptosis of MC38 colon carcinoma cells, induces a striking attraction of leukocytes both in an orthotopic model of colon carcinomatosis in vivo and in monocyte-migration assays in vitro. Leukocyte attraction depends on the presence of High Mobility Group Box 1 (HMGB1), an endogenous immune adjuvant and chemoattractant released by dying cells. Leukocyte recruitment is prevented in vivo and in vitro using blocking antibodies against HMGB1 and its competitive antagonist BoxA or by interfering with HMGB1 expression. Autophagy is required for leukocyte chemoattraction, since the latter abates upon pharmacological blockade of the autophagic flux while activation of autophagy per se, in the absence of death of colon carcinoma cells, is not sufficient to attract leukocytes. Our results identify autophagy induction and HMGB1 release in colon carcinoma cells as key events responsible for 5-FU elicited leukocyte attraction and define a novel rate-limiting target for combinatorial therapies.

Intravascular immunity as a key to systemic vasculitis: a work in progress, gaining momentum

Vascular inflammation contributes to the defence against invading microbes and to the repair of injured tissues. In most cases it resolves before becoming apparent. Vasculitis comprises heterogeneous clinical entities that are characterized by the persistence of vascular inflammation after it has served its homeostatic function. Most underlying mechanisms have so far remained elusive. Intravascular immunity refers to the surveillance of the vasculature by leucocytes that sense microbial or sterile threats to vessel integrity and initiate protective responses that entail most events that determine the clinical manifestations of vasculitis, such as end-organ ischaemia, neutrophil extracellular traps generation and thrombosis, leucocyte extravasation and degranulation. Understanding how the resolution of vascular inflammation goes awry in patients with systemic vasculitis will facilitate the identification of novel pharmacological targets and bring us a step closer in each patient to the selection of more effective and less toxic treatments.

Muscle atrophy, ubiquitin-proteasome, and autophagic pathways in dysferlinopathy

INTRODUCTION

Muscle fiber atrophy and the molecular pathways underlying this process have not been investigated in dysferlinopathy patients.

METHODS

In 22 muscles from dysferlinopathy patients we investigated fiber atrophy by morphometry and ubiquitin-proteasome and autophagic pathways using protein and/or transcriptional analysis of atrophy- and autophagy-related genes (MuRF1, atrogin1, LC3, p62, Bnip3).

RESULTS

Dysferlinopathy showed significant fiber atrophy and higher MuRF-1 protein and mRNA levels, which correlated with fiber size, suggesting activation of the atrophy program by proteasome induction.

CONCLUSIONS

Some of the MuRF-1 upregulation and proteasome induction may be attributed to the prominent regeneration found. A potential role of impaired autophagy was suggested by p62-positive protein aggregates in atrophic fibers and significantly higher levels of LC3-II and p62 proteins and overexpression of p62 and Bnip3 mRNA. Damaged muscle fibers and prominent inflammatory changes may also enhance autophagy due to the insufficient level of proteasomal degradation of mutant dysferlin.

Leukocyte HMGB1 is required for vessel remodeling in regenerating muscles

Signals of tissue necrosis, damage-associated molecular patterns (DAMPs), cause inflammation. Leukocytes migrating into injured tissues tonically release DAMPs, including the high mobility group box 1 protein (HMGB1). In the absence of suitable models, the relative role of DAMPs released because of necrosis or leukocyte activation has not, so far, been dissected. We have generated a mouse model lacking Hmgb1 in the hematopoietic system and studied the response to acute sterile injury of the skeletal muscle. Regenerating fibers are significantly less numerous at earlier time points and smaller at the end of the process. Leukocyte Hmgb1 licenses the skeletal muscle to react to hypoxia, to express angiopoietin-2, and to initiate angiogenesis in response to injury. Vascularization of the regenerating tissue is selectively jeopardized in the absence of leukocyte Hmgb1, revealing that it controls the nutrient and oxygen supply to the regenerating tissue. Altogether, our results reveal a novel nonredundant role for leukocyte Hmgb1 in the repair of injured skeletal muscle.

Macrophage plasticity in skeletal muscle repair

Macrophages are one of the first barriers of host defence against pathogens. Beyond their role in innate immunity, macrophages play increasingly defined roles in orchestrating the healing of various injured tissues. Perturbations of macrophage function and/or activation may result in impaired regeneration and fibrosis deposition as described in several chronic pathological diseases. Heterogeneity and plasticity have been demonstrated to be hallmarks of macrophages. In response to environmental cues they display a proinflammatory (M1) or an alternative anti-inflammatory (M2) phenotype. A lot of evidence demonstrated that after acute injury M1 macrophages infiltrate early to promote the clearance of necrotic debris, whereas M2 macrophages appear later to sustain tissue healing. Whether the sequential presence of two different macrophage populations results from a dynamic shift in macrophage polarization or from the recruitment of new circulating monocytes is a subject of ongoing debate. In this paper, we discuss the current available information about the role that different phenotypes of macrophages plays after injury and during the remodelling phase in different tissue types, with particular attention to the skeletal muscle.

Inflammation, DAMPs, tumor development, and progression: a vicious circle orchestrated by redox signaling

SIGNIFICANCE

Increasing evidence indicates that cancer development and progression are promoted by the joint action of redox distress and inflammation, supporting the potential impact of therapies aimed at restoring the redox homeostasis and fighting inflammation.

RECENT ADVANCES

Most of the literature of the last 40 years converges to the view that continuous oxidative stress and chronic inflammation sustain each other, leads to transformation of a normal cell to a neoplastic cell, and promotes tumor progression. Some recent findings, however, support an alternative model whereby the increased production of reactive oxygen species (ROS) is an attempt to defend more than a pathogenetic factor in cancer. Rather, tumor development and progression may be promoted by an excess of antioxidants, induced in both transformed cells and recruited inflammatory cells as an adaptive response to ROS.

CRITICAL ISSUES

Although the link among redox stress, chronic inflammation, and cancer is widely recognized, the underlying mechanisms are far to be understood. The redox unbalance of the microenvironment is likely to modulate the bioactivity of damage-associated molecular pattern molecules such as HMGB1, which are released by stressed tissues and play pleiotropic functions on tumor and inflammatory cells, but how this occur, and the relevant consequences, are still unclear.

FUTURE DIRECTIONS

In vivo measurement of cell redox status is an important challenge for future investigations. The improvement of the methodologies for ROS and antioxidant detection will allow a better understanding of the redox-related events in the tumor microenvironment with tremendous application potential in the development of rational combination therapies for cancer treatment.

Oxidative stress elicits platelet/leukocyte inflammatory interactions via HMGB1: a candidate for microvessel injury in sytemic sclerosis

AIMS

An abnormal generation of reactive oxygen species (ROS) is thought to contribute to systemic sclerosis (SSc), fostering autoimmunity, fibrosis, and vascular inflammation. The function of the prototypic damage-associated molecular pattern, high mobility group box 1 (HMGB1), depends on its redox status. Here we investigate whether oxidative stress regulates the cross-talk between leukocytes and platelets via HMGB1, thus contributing to vessel inflammation in SSc.

RESULTS

The oxidation of HMGB1 amplified its ability to activate neutrophils, as detected assessing the redistribution of primary granule molecules and the transactivation of the β2 integrin chain CD18. Activated platelets are a source of bioactive HMGB1 and via P-selectin stimulated neutrophils to generate ROS. Oxidized extracellular HMGB1, soluble or associated to platelet membrane or to platelet-derived microparticles (PDμPs), further increased leukocyte activation. Leukocyte activation abated in the presence of inhibitors of HMGB1 or of catalase, which catalyzes the dismutation of hydrogen peroxide into water and molecular oxygen. The redistribution of the content of primary granules and the transactivation of β2 integrins characterized blood leukocytes of SSc patients and membrane HMGB1 was significantly higher in patients with pulmonary hypertension or with diffuse SSc. HMGB1(+) microparticles (μPs) purified from SSc patients, but not HMGB1(-) μPs purified from control subjects, activated in vitro healthy neutrophils, and HMGB1 inhibitors reversed the effects of μPs.

INNOVATION AND CONCLUSION

ROS dramatically increase the ability of extracellular HMGB1 to activate blood leukocytes. This event might contribute to maintain the microvascular injury of patients with SSc.

HMGB1 localization during experimental periodontitis

AIM

This study sought to investigate the in vitro expression profile of high mobility group box 1 (HMGB1) in murine periodontal ligament fibroblasts (mPDL) stimulated with LPS or IL-1β and in vivo during ligature- or LPS-induced periodontitis in rats.

MATERIAL AND METHODS

For the in vivo study, 36 rats were divided into experimental and control groups, and biopsies were harvested at 7-30 d following disease induction. Bone loss and inflammation were evaluated. HMGB1 expression was assessed by immunohistochemistry, qPCR, and Western blot.

RESULTS

Significant increases in mPDL HMGB1 mRNA occurred at 4, 8, and 12 h with protein expression elevated by 24 h. HMGB1 mRNA expression in gingival tissues was significantly increased at 15 d in the LPS-PD model and at 7 and 15 d in the ligature model. Immunohistochemical staining revealed a significant increase in the number of HMGB1-positive cells during the experimental periods.

CONCLUSION

The results show that PDL cells produce HMGB1, which is increased and secreted extracellularly after inflammatory stimuli. In conclusion, this study demonstrates that HMGB1 may be associated with the onset and progression of periodontitis, suggesting that further studies should investigate the potential role of HMGB1 on periodontal tissue destruction.

Integrating phenotypic plasticity within an Ecological Genomics framework: recent insights from the genomics, evolution, ecology, and fitness of plasticity

E.B. Ford's 1964 book Ecological Genetics was a call for biologists to engage in multidisciplinary work in order to elucidate the link between genotype, phenotype, and fitness for ecologically relevant traits. In this review, we argue that the integration of an ecological genomics framework in studies of phenotypic plasticity is a promising approach to elucidate the causal links between genes and the environment, particularly during colonization of novel environments, environmental change, and speciation. This review highlights some of the questions and hypotheses generated from a mechanistic, evolutionary, and ecological perspective, in order to direct the continued and future use of genomic tools in the study of phenotypic plasticity.

The role of high mobility group box chromosomal protein 1 in rheumatoid arthritis

High mobility group box chromosomal protein 1 (HMGB1) is a ubiquitous highly conserved single polypeptide in all mammal eukaryotic cells. HMGB1 exists mainly within the nucleus and acts as a DNA chaperone. When passively released from necrotic cells or actively secreted into the extracellular milieu in response to appropriate signal stimulation, HMGB1 binds to related cell signal transduction receptors, such as RAGE, TLR2, TLR4 and TLR9, and becomes a proinflammatory cytokine that participates in the development and progression of many diseases, such as arthritis, acute lung injury, graft rejection immune response, ischaemia reperfusion injury and autoimmune liver damage. Only a small amount of HMGB1 release occurs during apoptosis, which undergoes oxidative modification on Cys106 and delivers tolerogenic signals to suppress immune activity. This review focuses on the important role of HMGB1 in the pathogenesis of RA, mainly manifested as the aberrant expression of HMGB1 in the serum, SF and synovial tissues; overexpression of signal transduction receptors; abnormal regulation of osteoclastogenesis and bone remodelling leading to the destruction of cartilage and bones. Intervention with HMGB1 may ameliorate the pathogenic conditions and attenuate disease progression of RA. Therefore administration of an HMGB1 inhibitor may represent a promising clinical approach for the treatment of RA.

Oxygen consumption and usage during physical exercise: the balance between oxidative stress and ROS-dependent adaptive signaling

The complexity of human DNA has been affected by aerobic metabolism, including endurance exercise and oxygen toxicity. Aerobic endurance exercise could play an important role in the evolution of Homo sapiens, and oxygen was not important just for survival, but it was crucial to redox-mediated adaptation. The metabolic challenge during physical exercise results in an elevated generation of reactive oxygen species (ROS) that are important modulators of muscle contraction, antioxidant protection, and oxidative damage repair, which at moderate levels generate physiological responses. Several factors of mitochondrial biogenesis, such as peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α), mitogen-activated protein kinase, and SIRT1, are modulated by exercise-associated changes in the redox milieu. PGC-1α activation could result in decreased oxidative challenge, either by upregulation of antioxidant enzymes and/or by an increased number of mitochondria that allows lower levels of respiratory activity for the same degree of ATP generation. Endogenous thiol antioxidants glutathione and thioredoxin are modulated with high oxygen consumption and ROS generation during physical exercise, controlling cellular function through redox-sensitive signaling and protein-protein interactions. Endurance exercise-related angiogenesis, up to a significant degree, is regulated by ROS-mediated activation of hypoxia-inducible factor 1α. Moreover, the exercise-associated ROS production could be important to DNA methylation and post-translation modifications of histone residues, which create heritable adaptive conditions based on epigenetic features of chromosomes. Accumulating data indicate that exercise with moderate intensity has systemic and complex health-promoting effects, which undoubtedly involve regulation of redox homeostasis and signaling.

Magnetic resonance imaging at 7T reveals common events in age-related sarcopenia and in the homeostatic response to muscle sterile injury

Skeletal muscle remodeling in response to various noxae physiologically includes structural changes and inflammatory events. The possibility to study those phenomena in-vivo has been hampered by the lack of validated imaging tools. In our study, we have relied on multiparametric magnetic resonance imaging for quantitative monitoring of muscle changes in mice experiencing age-related sarcopenia or active regeneration after sterile acute injury of tibialis anterior muscle induced by cardiotoxin (CTX) injection. The extent of myofibrils’ necrosis, leukocyte infiltration, and regeneration have been evaluated and compared with parameters from magnetic resonance imaging: T2-mapping (T2 relaxation time; T2-rt), diffusion-tensor imaging (fractional anisotropy, F.A.) and diffusion weighted imaging (apparent diffusion coefficient, ADC). Inflammatory leukocytes within the perimysium and heterogeneous size of fibers characterized aged muscles. They displayed significantly increased T2-rt (P<0.05) and F.A. (P<0.05) compared with young muscles. After acute damage T2-rt increased in otherwise healthy young muscles with a peak at day 3, followed by a progressive decrease to basal values. F.A. dropped 24 hours after injury and afterward increased above the basal level in the regenerated muscle (from day 7 to day 15) returning to the basal value at the end of the follow up period. The ADC displayed opposite kinetics. T2-rt positively correlated with the number of infiltrating leucocytes retrieved by immunomagnetic bead sorting from the tissue (r = 0.92) and with the damage/infiltration score (r = 0.88) while F.A. correlated with the extent of tissue regeneration evaluated at various time points after injury (r = 0.88). Our results indicate that multiparametric MRI is a sensitive and informative tool for monitoring inflammatory and structural muscle changes in living experimental animals; particularly, it allows identifying the increase of T2-rt and F.A. as common events reflecting inflammatory infiltration and muscle regeneration in the transient response of the tissue to acute injury and in the persistent adaptation to aging.

Endometriosis, a disease of the macrophage

Endometriosis, a common cause of pelvic pain and female infertility, depends on the growth of vascularized endometrial tissue at ectopic sites. Endometrial fragments reach the peritoneal cavity during the fertile years: local cues decide whether they yield endometriotic lesions. Macrophages are recruited at sites of hypoxia and tissue stress, where they clear cell debris and heme-iron and generate pro-life and pro-angiogenesis signals. Macrophages are abundant in endometriotic lesions, where are recruited and undergo alternative activation. In rodents macrophages are required for lesions to establish and to grow; bone marrow-derived Tie-2 expressing macrophages specifically contribute to lesions neovasculature, possibly because they concur to the recruitment of circulating endothelial progenitors, and sustain their survival and the integrity of the vessel wall. Macrophages sense cues (hypoxia, cell death, iron overload) in the lesions and react delivering signals to restore the local homeostasis: their action represents a necessary, non-redundant step in the natural history of the disease. Endometriosis may be due to a misperception of macrophages about ectopic endometrial tissue. They perceive it as a wound, they activate programs leading to ectopic cell survival and tissue vascularization. Clearing this misperception is a critical area for the development of novel medical treatments of endometriosis, an urgent and unmet medical need.

Requirement of inducible nitric oxide synthase for skeletal muscle regeneration after acute damage

Adult skeletal muscle regeneration results from activation, proliferation, and fusion of muscle stem cells, such as myogenic precursor cells. Macrophages are consistently present in regenerating skeletal muscles and participate into the repair process. The signals involved in the cross-talk between various macrophage populations and myogenic precursor cells have been only partially identified. In this study, we show a key role of inducible NO synthase (iNOS), expressed by classically activated macrophages in the healing of skeletal muscle. We found that, after sterile injury, iNOS expression is required for effective regeneration of the tissue, as myogenic precursor cells in the muscle of injured iNOS(-/-) mice fail to proliferate and differentiate. We also found that iNOS modulates inflammatory cell recruitment: damaged muscles of iNOS(-/-) animals express significantly higher levels of chemokines such as MIP2, MCP1, MIP-1α, and MCP1, and display more infiltrating neutrophils after injury and a persistence of macrophages at later time points. Finally, we found that iNOS expression in the injured muscle is restricted to infiltrating macrophages. To our knowledge, these data thus provide the first evidence that iNOS expression by infiltrating macrophages contributes to muscle regeneration, revealing a novel mechanism of inflammation-dependent muscle healing.

The pharmacologic inhibition of the xc- antioxidant system improves the antitumor efficacy of COX inhibitors in the in vivo model of 3-MCA tumorigenesis

The chemopreventive and therapeutic efficacy of the cyclooxygenase (COX) inhibitor ibuprofen (IB) and of sulfasalazine (SASP), a drug that targets the antioxidant xc- system, were exploited in the experimental model of 3-methylcholantrene (3-MCA)-induced mouse sarcoma. The chemopreventive treatments gave unsatisfactory results because administration of IB one day after the 3-MCA injection only slightly delayed the tumor development, whereas SASP dispensed under the same conditions resulted in accelerated tumorigenesis. Similarly, the therapeutic treatment with either drug, administrated daily from the tumor detection, decreased the proliferation rate of tumor cells and increased the survival of treated mice only at a low extent. Remarkably, the combined chemopreventive treatment with IB and therapeutic treatment with SASP displayed a better efficacy, with strong delay of sarcoma growth, reduced tumor size and increased survival of treated mice. The two drugs target not only tumor cells but also tumor-associated macrophages that were dramatically decreased in the tumor infiltrate of mice subjected to the combined treatment. The synergistic effects of the association between a broad anti-inflammatory compound, such as IB, and a redox-directed drug, such as SASP, shed new light in the role of inflammation and of the redox response in chemical tumorigenesis and point to the combined chemopreventive plus therapeutic treatment with IB and SASP as a promising novel approach for antitumor therapy.

Transplanted mesoangioblasts require macrophage IL-10 for survival in a mouse model of muscle injury

The aim of this study was to verify whether macrophages influence the fate of transplanted mesoangioblasts--vessel-associated myogenic precursors--in a model of sterile toxin-induced skeletal muscle injury. We have observed that in the absence of macrophages, transplanted mesoangioblasts do not yield novel fibers. Macrophages retrieved from skeletal muscles at various times after injury display features that resemble those of immunoregulatory macrophages. Indeed, they secrete IL-10 and express CD206 and CD163 membrane receptors and high amounts of arginase I. We have reconstituted the muscle-associated macrophage population by injecting polarized macrophages before mesoangioblast injection: alternatively activated, immunoregulatory macrophages only support mesoangioblast survival and function. This action depends on the secretion of IL-10 in the tissue. Our results reveal an unanticipated role for tissue macrophages in mesoangioblast function. Consequently, the treatment of muscle disorders with mesoangioblasts should take into consideration coexisting inflammatory pathways, whose activation may prove crucial for its success.