Blocking TRAIL-DR5 signaling with soluble DR5 reduces delayed neuronal damage after transient global cerebral ischemia

Molecular signatures in prion disease: altered death receptor pathways in a mouse model

BACKGROUND

Prion diseases are transmissible and fatal neurodegenerative diseases characterized by accumulation of misfolded prion protein isoform (PrPSc), astrocytosis, microgliosis, spongiosis, and neurodegeneration. Elevated levels of cell membrane associated PrPSc protein and inflammatory cytokines hint towards the activation of death receptor (DR) pathway/s in prion diseases. Activation of DRs regulate, either cell survival or apoptosis, autophagy and necroptosis based on the adaptors they interact. Very little is known about the DR pathways activation in prion disease. DR3 and DR5 that are expressed in normal mouse brain were never studied in prion disease, so also their ligands and any DR adaptors. This research gap is notable and investigated in the present study.

METHODS

C57BL/6J mice were infected with Rocky Mountain Laboratory scrapie mouse prion strain. The progression of prion disease was examined by observing morphological and behavioural abnormalities. The levels of PrP isoforms and GFAP were measured as the marker of PrPSc accumulation and astrocytosis respectively using antibody-based techniques that detect proteins on blot and brain section. The levels of DRs, their glycosylation and ectodomain shedding, and associated factors warrant their examination at protein level, hence western blot analysis was employed in this study.

RESULTS

Prion-infected mice developed motor deficits and neuropathology like PrPSc accumulation and astrocytosis similar to other prion diseases. Results from this research show higher expression of all DR ligands, TNFR1, Fas and p75NTR but decreased levels DR3 and DR5. The levels of DR adaptor proteins like TRADD and TRAF2 (primarily regulate pro-survival pathways) are reduced. FADD, which primarily regulate cell death, its level remains unchanged. RIPK1, which regulate pro-survival, apoptosis and necroptosis, its expression and proteolysis (inhibits necroptosis but activates apoptosis) are increased.

CONCLUSIONS

The findings from the present study provide evidence towards the involvement of DR3, DR5, DR6, TL1A, TRAIL, TRADD, TRAF2, FADD and RIPK1 for the first time in prion diseases. The knowledge obtained from this research discuss the possible impacts of these 16 differentially expressed DR factors on our understanding towards the multifaceted neuropathology of prion diseases and towards future explorations into potential targeted therapeutic interventions for prion disease specific neuropathology.

Circulating cytokines and vascular dementia: A bi-directional Mendelian randomization study

Inflammatory responses are associated with the development of vascular dementia (VaD). Circulating cytokines modulate the inflammatory response and are important for the immune system. To further elucidate the role of the immune system in VaD, we used Mendelian randomization (MR) to comprehensively and bi-directionally assess the role of circulating cytokines in VaD. Using state-of-the-art genome-wide association studies, we primarily assessed whether different genetic levels of 41 circulating cytokines affect the risk of developing VaD and, in turn, whether the genetic risk of VaD affects these circulating cytokines. We used inverse variance weighting (IVW) and several other MR methods to assess the bidirectional causality between circulating cytokines and VaD, and performed sensitivity analyses. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) was inversely associated with VaD risk [odds ratio (OR): 0.74, 95 % confidence interval (CI): 0.60-0.92, P = 0.007, 0.007]. VaD was associated with seven circulating cytokines: macrophage inflammatory protein 1b (MIP-1 beta) [OR: 1.05, 95 % CI: 1.01-1.08, P = 0.009], Interleukin-12p70 (IL-12) [OR: 1.04, 95 % CI: 1.00-1.08, P = 0.047], Interleukin-17 (IL-17) [OR: 1.04, 95 % CI: 1.00-1.07, P = 0.038], Interleukin-7 (IL-7) [OR: 1.07, 95 % CI: 1.02-1.12, P = 0.009], Interferon gamma (IFN-γ) [OR: 1.03, 95 % CI: 1.00-1.07, P = 0.046], Granulocyte-colony stimulating factor (GCSF) [OR: 1.06, 95 % CI: 1.02-1.09, P = 0.001], Fibroblast growth factor (FGF) [P = 0.001], and Fibroblast growth factor (FGF) [P = 0.001]. Fibroblast growth factor basic (FGF-Basic) [OR: 1.04, 95 % CI: 1.01-1.08, P = 0.02] were positively correlated. Circulating cytokines are associated with VaD, and further studies are needed to determine whether they are effective targets for intervention to prevent or treat VaD.

Proteomic profiling identifies novel inflammation-related plasma proteins associated with ischemic stroke outcome

BACKGROUND

The inflammatory response to cerebral ischemia is complex; however, most clinical studies of stroke outcome focus on a few selected proteins. We, therefore, aimed to profile a broad range of inflammation-related proteins to: identify proteins associated with ischemic stroke outcome that are independent of established clinical predictors; identify proteins subsets for outcome prediction; and perform sex and etiological subtype stratified analyses.

METHODS

Acute-phase plasma levels of 65 inflammation-related proteins were measured in 534 ischemic stroke cases. Logistic regression was used to estimate associations to unfavorable 3-month functional outcome (modified Rankin Scale score > 2) and LASSO regressions to identify proteins with independent effects.

RESULTS

Twenty proteins were associated with outcome in univariable models after correction for multiple testing (FDR < 0.05), and for 5 the association was independent of clinical variables, including stroke severity (TNFSF14 [LIGHT], OSM, SIRT2, STAMBP, and 4E-BP1). LASSO identified 9 proteins that could best separate favorable and unfavorable outcome with a predicted diagnostic accuracy (AUC) of 0.81; three associated with favorable (CCL25, TRAIL [TNFSF10], and Flt3L) and 6 with unfavorable outcome (CSF-1, EN-RAGE [S100A12], HGF, IL-6, OSM, and TNFSF14). Finally, we identified sex- and etiologic subtype-specific associations with the best discriminative ability achieved for cardioembolic, followed by cryptogenic stroke.

CONCLUSIONS

We identified candidate blood-based protein biomarkers for post-stroke functional outcome involved in, e.g., NLRP3 inflammasome regulation and signaling pathways, such as TNF, JAK/STAT, MAPK, and NF-κB. These proteins warrant further study for stroke outcome prediction as well as investigations into the putative causal role for stroke outcome.

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

TRAIL or TRAIL-R2 as a Predictive Biomarker for Mortality or Cardiovascular Events: A Systematic Review and Meta-analysis

ABSTRACT

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and TRAIL-receptor-2 (TRAIL-R2) are associated with atherosclerosis. This meta-analysis aimed to investigate the potential association between TRAIL/TRAIL-R2 with mortality or cardiovascular (CV) events. PubMed, Embase, and Cochrane Library were searched for reports published up to May 2021. Reports were included when the association between TRAIL or TRAIL-R2 and mortality or CV events was reported. Considering the heterogeneity between studies, we used the random-effects model for all analyses. Ultimately, the meta-analysis included 18 studies (16,295 patients). The average follow-up ranged from 0.25 to 10 years. Decreased TRAIL levels were negatively associated with all-cause mortality [rank variable, hazard ratio (HR), 95% CI, 2.93, 1.94-4.42; I2 = 0.0%, Pheterogeneity = 0.835]. Increased TRAIL-R2 levels were positively associated with all-cause mortality (continuous variable, HR, 95% CI, 1.43, 1.23-1.65; I2 = 0.0%, Pheterogeneity = 0.548; rank variable, HR, 95% CI, 7.08, 2.70-18.56; I2 = 46.5%, Pheterogeneity = 0.154), CV mortality (continuous variable, HR, 95% CI, 1.33, 1.14-1.57; I2 = 0.0%, Pheterogeneity = 0.435), myocardial infarction (continuous variable, HR, 95% CI, 1.23, 1.02-1.49; rank variable, HR, 95% CI, 1.49, 1.26-1.76; I2 = 0.7%, Pheterogeneity = 0.402), and new-onset heart failure (rank variable, HR, 95% CI, 3.23, 1.32-7.87; I2 = 83.0%, Pheterogeneity = 0.003). In conclusion, decreased TRAIL was negatively associated with all-cause mortality, and increased TRAIL-R2 was positively associated with all-cause mortality, CV mortality, myocardial infarction, and heart failure.

TRAIL inhibition by soluble death receptor 5 protects against acute myocardial infarction in rats

Acute myocardial infarction (AMI) is associated with high morbidity and mortality. An effective therapeutic strategy is to rescue cardiomyocytes from death. Apoptosis is a key reason of cardiomyocyte death that can be prevented. In this study, we investigated the role of TNF-related apoptosis-inducing ligand (TRAIL) in initiating apoptosis by binding to death receptor 5 (DR5), and this procession is inhibited by soluble DR5 (sDR5) in rats after AMI. First, we found that the level of TRAIL in serum was down-regulated in AMI patients. Then, TRAIL and DR5 expression was analysed in the myocardium of rats after AMI, and their expression was up-regulated. sDR5 treatment reduced the myocardial infarct size and the levels of CK-MB and cTn-I in serum. The expression of caspase 3 and PARP is decreased, but the anti-apoptotic factor Bcl-2 was increased in sDR5 treatment rats after AMI. DR5 expression was also analysed after sDR5 treatment and it was down-regulated, and a low level of DR5 expression seemed to be beneficial for the myocardium. Overall, our findings indicated that sDR5 decreases myocardial damage by inhibiting apoptosis in rat after AMI. We expect to observe the potential therapeutic effects of sDR5 on AMI in the future.

Potential neurotoxic activity of diverse molecules released by astrocytes

Astrocytes are the main support cells of the central nervous system. They also participate in neuroimmune reactions. In response to pathological and immune stimuli, astrocytes transform to reactive states characterized by increased release of inflammatory mediators. Some of these molecules are neuroprotective and inflammation resolving while others, including reactive oxygen species (ROS), nitric oxide (NO), matrix metalloproteinase (MMP)- 9, L-glutamate, and tumor necrosis factor α (TNF), are well-established toxins known to cause damage to surrounding cells and tissues. We hypothesized that similar to microglia, the brain immune cells, reactive astrocytes can release a broader set of diverse molecules that are potentially neurotoxic. A literature search was conducted to identify such molecules using the following two criteria: 1) evidence of their expression and secretion by astrocytes and 2) direct neurotoxic action. This review describes 14 structurally diverse molecules as less-established astrocyte neurotoxins, including C-X-C motif chemokine ligand (CXCL)10, CXCL12/CXCL12(5-67), FS-7-associated surface antigen ligand (FasL), macrophage inflammatory protein (MIP)- 2α, TNF-related apoptosis inducing ligand (TRAIL), pro-nerve growth factor (proNGF), pro-brain-derived neurotrophic factor (proBDNF), chondroitin sulfate proteoglycans (CSPGs), cathepsin (Cat)B, group IIA secretory phospholipase A₂ (sPLA₂-IIA), amyloid beta peptides (Aβ), high mobility group box (HMGB)1, ceramides, and lipocalin (LCN)2. For some of these molecules, further studies are required to establish either their direct neurotoxic effects or the full spectrum of stimuli that induce their release by astrocytes. Only limited studies with human-derived astrocytes and neurons are available for most of these potential neurotoxins, which is a knowledge gap that should be addressed in the future. We also summarize available evidence of the role these molecules play in select neuropathologies where reactive astrocytes are a key feature. A comprehensive understanding of the full spectrum of neurotoxins released by reactive astrocytes is key to understanding neuroinflammatory diseases characterized by the adverse activation of these cells and may guide the development of novel treatment strategies.

Immunoprofiling of Nonarteritic Anterior Ischemic Optic Neuropathy

Purpose

Nonarteritic anterior ischemic optic neuropathy (NAION) is a common acute optic neuropathy in those older than 50 years. There is no blood diagnostic test or efficient treatment for NAION. We investigated the suitability of blood inflammatory proteins as biomarkers and therapeutic targets of NAION.

Methods

We conducted an exploratory, cross-sectional case-control study including 18 patients with NAION (n = 5 acute, and n = 13 chronic) and 9 controls. NAION was confirmed by clinical examination and optical coherence tomography. Subjects underwent peripheral blood collection; plasma was isolated within 2 hours and analyzed using a 76-plex array of cytokines, chemokines, and growth factors.

Results

In acute NAION, there was increased peripapillary retinal thickness on optical coherence tomography consistent with optic disc edema. Plasma profiling revealed dramatic changes in inflammatory proteins in NAION. Statistical analysis generated a list of 20 top-ranked molecules in NAION, with 15% overlap in acute and chronic NAION. Principal component analysis, hierarchical clustering, and Spearman correlation generally segregated controls, acute and chronic NAION, with some overlap. Longitudinal data from one patient demonstrated an evolving inflammatory pattern from acute to chronic NAION. In acute NAION, Eotaxin-3, MCP-2, TPO, and TRAIL were the top biomarker candidates. In chronic NAION, IL-1α and CXCL10 emerged as the strongest therapeutic targets.

Conclusions

Post-NAION inflammation occurs in both acute and chronic NAION. Statistical analysis of plasma profile changes generated a list of 20 potential biomarker and therapeutic targets of NAION.

Translational Relevance

We identified blood molecular targets to improve NAION diagnosis and treatment.

Brimonidine is Neuroprotective in Animal Paradigm of Retinal Ganglion Cell Damage

To investigate the neuroprotective effect of brimonidine after retinal ischemia damage on mouse eye. Glaucoma is an optic neuropathy characterized by retinal ganglion cells (RGCs) death, irreversible peripheral and central visual field loss, and high intraocular pressure. Ischemia reperfusion (I/R) injury model was used in C57BL/6J mice to mimic conditions of glaucomatous neurodegeneration. Mouse eyes were treated topically with brimonidine and pattern electroretinogram were used to assess the retinal ganglion cells (RGCs) function. A wide range of inflammatory markers, as well as anti-inflammatory and neurotrophic molecules, were investigated to figure out the potential protective effects of brimonidine in mouse retina. In particular, brain-derived neurotrophic factor (BDNF), IL-6, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its death receptor DR-5, TNF-α, GFAP, Iba-1, NOS, IL-1β and IL-10 were assessed in mouse retina that underwent to I/R insult with or without brimonidine treatment. Brimonidine provided remarkable RGCs protection in our paradigm. PERG amplitude values were significantly (p < 0.05) higher in brimonidine-treated eyes in comparison to I/R retinas. Retinal BDNF mRNA levels in the I/R group dropped significantly (p < 0.05) compared to the control group (normal mice); brimonidine treatment counteracted the downregulation of retinal BDNF mRNA in I/R eyes. Retinal inflammatory markers increased significantly (p < 0.05) in the I/R group and brimonidine treatment was able to revert that. The anti-inflammatory IL-10 decreased significantly (p < 0.05) after retinal I/R insult and increased significantly (p < 0.05) in the group treated with brimonidine. In conclusion, brimonidine was effective in preventing loss of function of RGCs and in regulating inflammatory biomarkers elicited by retinal I/R injury.

sDR5-Fc inhibits macrophage M1 polarization by blocking the glycolysis

BACKGROUND

M1 polarization of macrophages is an important pathological process in myocardial ischemia reperfusion injury, which is the major obstacle for the treatment of acute myocardial infarction. Currently, the strategies and mechanisms of inhibiting M1 polarization are poorly explored. This study aims to investigate the role of soluble death receptor 5-Fc (sDR5-Fc) in regulating M1 polarization of macrophages under extreme conditions and explore the mechanisms from the aspect of glycolysis.

METHODS

Extreme conditions were induced in RAW264.7 cells. Real-time quantitative polymerase chain reaction and western blot were used to detect the expression of mRNA and proteins, respectively. Cell counting kit-8 was used to investigate the proliferation activity of cells. Expression levels of inflammatory cytokines were determined by enzyme-linked immunosorbent assay.

RESULTS

We found that sDR5-Fc rescues the proliferation of macrophages under extreme conditions, including nutrition deficiency, excessive peroxide, and ultraviolet irradiation. In addition, administration of sDR5-Fc inhibits the M1 polarization of macrophages induced by lipopolysaccharide (LPS) and interferon-gamma (IFN-γ), as the expression of M1 polarization markers CD86, CXC motif chemokine ligand 10, matrix metalloproteinase 9, and tumor necrosis factor-α, as well as the secretion of inflammatory factors interleukin (IL)-1β and IL-6, were significantly decreased. By further investigation of the mechanisms, the results showed that sDR5-Fc can recover the LPS and IFN-γ induced pH reduction, lactic acid elevation, and increased expression of hexokinase 2 and glucose transporter 1, which were markers of glycolysis in macrophages.

CONCLUSIONS

sDR5-Fc inhibits the M1 polarization of macrophages by blocking the glycolysis, which provides a new direction for the development of strategies in the treatment of myocardial ischemia reperfusion injury.

TRAIL and Cardiovascular Disease-A Risk Factor or Risk Marker: A Systematic Review

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a pro-apoptotic protein showing broad biological functions. Data from animal studies indicate that TRAIL may possibly contribute to the pathophysiology of cardiomyopathy, atherosclerosis, ischemic stroke and abdominal aortic aneurysm. It has been also suggested that TRAIL might be useful in cardiovascular risk stratification. This systematic review aimed to evaluate whether TRAIL is a risk factor or risk marker in cardiovascular diseases (CVDs) focusing on major adverse cardiovascular events. Two databases (PubMed and Cochrane Library) were searched until December 2020 without a year limit in accordance to the PRISMA guidelines. A total of 63 eligible original studies were identified and included in our systematic review. Studies suggest an important role of TRAIL in disorders such as heart failure, myocardial infarction, atrial fibrillation, ischemic stroke, peripheral artery disease, and pulmonary and gestational hypertension. Most evidence associates reduced TRAIL levels and increased TRAIL-R2 concentration with all-cause mortality in patients with CVDs. It is, however, unclear whether low TRAIL levels should be considered as a risk factor rather than a risk marker of CVDs. Further studies are needed to better define the association of TRAIL with cardiovascular diseases.

Insight into the divergent role of TRAIL in non-neoplastic neurological diseases

Tumour necrosis factor–related apoptosis‐inducing ligand (TRAIL) is a member of the tumour necrosis factor (TNF) superfamily which mainly induces apoptosis of tumour cells and transformed cell lines with no systemic toxicity, whereas they share high sequence homology with TNF and CD95L. These unique effects of TRAIL have made it an important molecule in oncology research. However, the research on TRAIL‐related antineoplastic agents has lagged behind and has been limited by the extensive drug resistance in cancer cells. Given the several findings showing that TRAIL is involved in immune regulation and other pleiotropic biological effects in non‐malignant cells, TRAIL and its receptors have attracted widespread attention from researchers. In the central nervous system (CNS), TRAIL is highly correlated with malignant tumours such as glioma and other non‐neoplastic disorders such as acute brain injury, CNS infection and neurodegenerative disease. Many clinical and animal studies have revealed the dual roles of TRAIL in which it causes damage by inducing cell apoptosis, and confers protection by enhancing both pro‐ and non‐apoptosis effects in different neurological disorders and at different sites or stages. Its pro‐apoptotic effect produces a pro‐survival effect that cannot be underestimated. This review extensively covers in vitro and in vivo experiments and clinical studies investigating TRAIL. It also provides a summary of the current knowledge on the TRAIL signalling pathway and its involvement in pathogenesis, diagnosis and therapeutics of CNS disorders as a basis for future research.

HIF-1α Mediates TRAIL-Induced Neuronal Apoptosis via Regulating DcR1 Expression Following Traumatic Brain Injury

Background: Neuronal apoptosis involved in secondary injury following traumatic brain injury (TBI) significantly contributes to the poor outcomes of patients with TBI. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can selectively induce apoptosis of tumor cells. Hypoxia factor (HIF) 1α is a controversial factor that mediates the neuronal apoptotic pathway. Herein, we hypothesize that HIF-1α may mediate the TRAIL-induced neuronal apoptosis after TBI.

Methods: We used Western blots and immunofluorescence to study the expression and cell localization of TRAIL and death receptor 5 (DR5) after TBI in rats. Soluble DR5 (sDR5) administration was used to block the TRAIL-induced neuronal death and neural deficits. HIF-1α inhibitor 2ME and agonist DMOG were used to study the role of HIF-1α in TRAIL-induced neuronal death. Meanwhile, HIF-1α siRNA was used to investigate the role of HIF-1α in TRAIL-induced neuronal death in vitro.

Results: The expressions of microglia-located TRAIL and neuron-located DR5 were significantly upregulated after TBI. sDR5 significantly attenuated TRAIL-induced neuronal apoptosis and neurological deficits. 2ME decreased neuronal apoptosis, lesion area, and brain edema and improved neurological function via increased expression of TRAIL decoy receptor 1 (DcR1), which inhibited TRAIL-induced apoptosis after TBI. The administration of DMOG produced the opposite effect than did 2ME. Similarly, HIF-1α siRNA attenuated TRAIL-induced neuronal death via increased DcR1 expression in vitro.

Conclusion: Our findings suggested that the TRAIL/DR5 signaling pathway plays an important role after neuronal apoptosis after TBI. HIF-1α mediates TRAIL-induced neuronal apoptosis by regulating DcR1 expression following TBI.

Modulator of apoptosis-1 is a potential therapeutic target in acute ischemic injury

Modulator of apoptosis 1 (MOAP-1) is a Bax-associating protein highly enriched in the brain. In this study, we examined the role of MOAP-1 in promoting ischemic injuries following a stroke by investigating the consequences of MOAP-1 overexpression or deficiency in in vitro and in vivo models of ischemic stroke. MOAP-1 overexpressing SH-SY5Y cells showed significantly lower cell viability following oxygen and glucose deprivation (OGD) treatment when compared to control cells. Consistently, MOAP-1^-/- primary cortical neurons were observed to be more resistant against OGD treatment than the MOAP-1^+/+ primary neurons. In the mouse transient middle cerebral artery occlusion (tMCAO) model, ischemia triggered MOAP-1/Bax association, suggested activation of the MOAP-1-dependent apoptotic cascade. MOAP-1^-/- mice were found to exhibit reduced neuronal loss and smaller infarct volume 24 h after tMCAO when compared to MOAP-1^+/+ mice. Correspondingly, MOAP-1^-/- mice also showed better integrity of neurological functions as demonstrated by their performance in the rotarod test. Therefore, both in vitro and in vivo data presented strongly support the conclusion that MOAP-1 is an important apoptotic modulator in ischemic injury. These results may suggest that a reduction of MOAP-1 function in the brain could be a potential therapeutic approach in the treatment of acute stroke.

Cell Death in the Developing Brain after Hypoxia-Ischemia

Perinatal insults such as hypoxia–ischemia induces secondary brain injury. In order to develop the next generation of neuroprotective therapies, we urgently need to understand the underlying molecular mechanisms leading to cell death. The cell death mechanisms have been shown to be quite different in the developing brain compared to that in the adult. The aim of this review is update on what cell death mechanisms that are operating particularly in the setting of the developing CNS. In response to mild stress stimuli a number of compensatory mechanisms will be activated, most often leading to cell survival. Moderate-to-severe insults trigger regulated cell death. Depending on several factors such as the metabolic situation, cell type, nature of the stress stimulus, and which intracellular organelle(s) are affected, the cell undergoes apoptosis (caspase activation) triggered by BAX dependent mitochondrial permeabilzation, necroptosis (mixed lineage kinase domain-like activation), necrosis (via opening of the mitochondrial permeability transition pore), autophagic cell death (autophagy/Na⁺, K⁺-ATPase), or parthanatos (poly(ADP-ribose) polymerase 1, apoptosis-inducing factor). Severe insults cause accidental cell death that cannot be modulated genetically or by pharmacologic means. However, accidental cell death leads to the release of factors (damage-associated molecular patterns) that initiate systemic effects, as well as inflammation and (regulated) secondary brain injury in neighboring tissue. Furthermore, if one mode of cell death is inhibited, another route may step in at least in a scenario when upstream damaging factors predominate over protective responses. The provision of alternative routes through which the cell undergoes death has to be taken into account in the hunt for novel brain protective strategies.

TRAIL facilitates cytokine expression and macrophage migration during hypoxia/reoxygenation via ER stress-dependent NF-κB pathway

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which is known as a key molecule to induce cancer cell apoptosis, has also been found to participate in the process of ischemia/reperfusion (I/R) injury. Infiltrated macrophages play dual roles in inflammatory injury and healing following I/R. Whether TRAIL has any effect on macrophages during this process remains elusive. Here we showed that I/R triggered the expressions of TRAIL, DR5 and cytokines (IL-1β, TNFα, CCL-2 and ICAM-1), in addition to macrophage infiltration, which could be abolished by TRAIL neutralizing antibody. In vitro, TRAIL enhanced DR5 expression and facilitated the macrophages migration following hypoxia/reoxygenation (H/R) treatment in a dose-dependent manner via ER stress and NF-κB signaling pathways, which is accompanied by inflammatory factors expression. The increased cytokines production (such as TNFα and IL-1β) stimulated by TRAIL can be blocked by the NF-κB and ER stress inhibitor. The results also suggested that NF-κB activation of macrophages during H/R was regulated by ER stress. Thus, our research present that TRAIL affects functional activities of macrophages during I/R injury, which may be a potential therapeutic target for ischemic heart disease.

Clinical perspectives of TRAIL: insights into central nervous system disorders

The TNF-related apoptosis inducing ligand TRAIL is a member of the TNF superfamily that has been firstly studied and evaluated for its anti-cancer activity, and the insights into its biology have already led to the identification of several TRAIL-based anticancer strategies with strong clinical therapeutic potentials. Nonetheless, the TRAIL system is far more complex and it can lead to a wider range of biological effects other than the ability of inducing apoptosis in cancer cells. By virtue of the different receptors and the different signalling pathways involved, TRAIL plays indeed a role in the regulation of different processes of the innate and adaptive immune system and this feature makes it an intriguing molecule under consideration in the development/progression/treatment of several immunological disorders. In this context, central nervous system represents a peculiar anatomic site where, despite its "status" of immune-privileged site, both innate and adaptive inflammatory responses occur and are involved in several pathological conditions. A number of studies have evaluated the role of TRAIL and of TRAIL-related pathways as pro-inflammatory or protective stimuli, depending on the specific pathological condition, confirming a twofold nature of this molecule. In this light, the aim of this review is to summarize the main preclinical evidences of the potential/involvement of TRAIL molecule and TRAIL pathways for the treatment of central nervous system disorders and the key suggestions coming from their assessment in preclinical models as proof of concept for future clinical studies.

Activation of TRAIL-DR5 pathway promotes sensorineural degeneration in the inner ear

Tumor necrosis factor (TNF) family cytokines are important mediators of inflammation. Elevated levels of serum TNF‐α are associated with human sensorineural hearing loss via poorly understood mechanisms. We demonstrate, for the first time, expression of TNF‐related apoptosis‐inducing ligand (TRAIL) and its signaling death receptor 5 (DR5) in the murine inner ear and show that exogenous TRAIL can trigger hair cell and neuronal degeneration, which can be partly prevented with DR5‐blocking antibodies.

Remote Limb Preconditioning Generates a Neuroprotective Effect by Modulating the Extrinsic Apoptotic Pathway and TRAIL-Receptors Expression

As remote limb preconditioning (RPC) ameliorates brain damage after ischemic cerebral stroke (ICS), the purpose of the present study was to explore the molecular mechanisms in the course of RPC. Results of TUNEL staining and cleaved caspase-3 expression showed that ischemia-induced neuronal apoptosis was inhibited by RPC. The expression changes in cleaved caspase-8, cFLIP, Bid itself, and its truncated form represented that RPC suppressed the activation of extrinsic apoptotic pathway during ICS. Then, the level of cytoplasmic cytochrome c was also decreased by RPC. In addition, RPC might partially suppress TNF-related apoptosis-inducing ligand (TRAIL)-induced extrinsic apoptosis through downregulation of TRAIL death receptors and upregulation of TRAIL decoy receptors. As a counterproof, immunoneutralization of TRAIL in dMCAO rats resulted in significant restraint of tissue damage and in a marked functional recovery. Our data complemented the knowledge of RPC neuroprotective mechanism and provided new evidence for its clinical application.

Inflammation-induced sensitization of the brain in term infants

Perinatal insults are a leading cause of infant mortality and amongst survivors are frequently associated with neurocognitive impairment, cerebral palsy (CP), and seizure disorders. The events leading to perinatal brain injury are multifactorial. This review describes how one subinjurious factor affecting the brain sensitizes it to a second injurious factor, causing an exacerbated injurious cascade. We will review the clinical and experimental evidence, including observations of high rates of maternal and fetal infections in term-born infants with neonatal encephalopathy and cerebral palsy. In addition, we will discuss preclinical evidence for the sensitizing effects of inflammation on injuries, such as hypoxia-ischaemia, our current understanding of the mechanisms underpinning the sensitization process, and the possibility for neuroprotection.

Role of mitochondria in apoptotic and necroptotic cell death in the developing brain

Hypoxic–ischemic encephalopathy induces secondary brain injury characterized by delayed energy failure. Currently, therapeutic hypothermia is the sole treatment available after severe intrapartum asphyxia in babies and acts to attenuate secondary loss of high energy phosphates improving both short- and long-term outcome. In order to develop the next generation of neuroprotective therapies, we urgently need to understand the underlying molecular mechanisms leading to cell death. Hypoxia–ischemia creates a toxic intracellular environment including accumulation of reactive oxygen/nitrosative species and intracellular calcium after the insult, inducing mitochondrial impairment. More specifically mitochondrial respiration is suppressed and calcium signaling is dysregulated. At a certain threshold, Bax-dependent mitochondrial permeabilization will occur leading to activation of caspase-dependent and apoptosis-inducing factor-dependent apoptotic cell death. In addition, hypoxia–ischemia induces inflammation, which leads to the release of TNF-α, TRAIL, TWEAK, FasL and Toll-like receptor agonists that will activate death receptors on neurons and oligodendroglia. Death receptors trigger apoptotic death via caspase-8 and necroptotic cell death through formation of the necrosome (composed of RIP1, RIP3 and MLKL), both of which converge at the mitochondria.

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Hypoxic-ischemic encephalopathy induces secondary brain injury characterized by delayed energy failure and excitotoxicity.

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Hypoxia-ischemia triggers accumulation of reactive oxygen species andintracellular calcium, which induces mitochondrial dysfunction.

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Mitochondrial impairment can cause Bax-dependent mitochondrial permeabilization, which triggers release of pro-apoptotic proteins and cell death.

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During the recovery phase, Inflammation is produced leading to death receptor activation and induction of necroptosis.

Pinocembrin alleviates memory impairment in transient global cerebral ischemic rats

The aim of the present study was to investigate the effect of pinocembrin on cognitive ability impairment in a rat model of transient global cerebral ischemia (TGCI). The TGCI model was established by inducing global cerebral ischemia for 20 min, followed by reperfusion for two weeks. The rats were divided into five experimental groups, including the sham group that were not subjected to ischemia, and four ischemic groups where the rats were exposed to TGCI. The sham and control TGCI groups were administered a vehicle intravenously immediately after reperfusion, while the other three groups were intravenously treated with 1, 5 and 10 mg/kg pinocembrin, respectively. In the present study, neurological scores were analyzed at 0 and 24 h after reperfusion, and the effect of pinocembrin on cognitive ability impairment in the TGCI rat model was investigated using a Morris water maze test. Neuronal loss was observed under an optical microscope with the assistance of Nissl staining. In addition, glial fibrillary acidic protein (GFAP)-positive cells were observed under an optical microscope by an immunohistochemistry assay. Pinocembrin treatment was found to alleviate the cognitive impairments, decrease the neurological scores, diminish neuronal loss in the hippocampus and reduce the number of GFAP-positive cells in the hippocampal CA1 region of the TGCI rats. Therefore, pinocembrin alleviated memory impairment in the TGCI rats.

Ischemic tolerance modulates TRAIL expression and its receptors and generates a neuroprotected phenotype

TNF-related apoptosis inducing ligand (TRAIL), a member of the TNF superfamily released by microglia, appears to be involved in the induction of apoptosis following focal brain ischemia. Indeed, brain ischemia is associated with progressive enlargement of damaged areas and prominent inflammation. As ischemic preconditioning reduces inflammatory response to brain ischemia and ameliorates brain damage, the purpose of the present study was to evaluate the role of TRAIL and its receptors in stroke and ischemic preconditioning and to propose, by modulating TRAIL pathway, a new therapeutic strategy in stroke. In order to achieve this aim a rat model of harmful focal ischemia, obtained by subjecting animals to 100 min of transient occlusion of middle cerebral artery followed by 24 h of reperfusion and a rat model of ischemic preconditioning in which the harmful ischemia was preceded by 30 mins of tMCAO, which represents the preconditioning protective stimulus, were used. Results show that the neuroprotection elicited by ischemic preconditioning occurs through both upregulation of TRAIL decoy receptors and downregulation of TRAIL itself and of its death receptors. As a counterproof, immunoneutralization of TRAIL in tMCAO animals resulted in significant restraint of tissue damage and in a marked functional recovery. Our data shed new light on the mechanisms that propagate ongoing neuronal damage after ischemia in the adult mammalian brain and provide new molecular targets for therapeutic intervention. Strategies aimed to repress the death-inducing ligands TRAIL, to antagonize the death receptors, or to activate the decoy receptors open new perspectives for the treatment of stroke.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) signaling and cell death in the immature central nervous system after hypoxia-ischemia and inflammation

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the TNF family. The interaction of TRAIL with death receptor 4 (DR4) and DR5 can trigger apoptotic cell death. The aim of this study was to investigate the role of TRAIL signaling in neonatal hypoxia-ischemia (HI). Using a neonatal mouse model of HI, mRNA, and protein expression of TRAIL, DR5 and the TRAIL decoy receptors osteoprotegerin (OPG), mDcTRAILR1, and mDcTRAILR2 were determined. In vitro, mRNA expression of these genes was measured in primary neurons and oligodendrocyte progenitor cells (OPCs) after inflammatory cytokine (TNF-α/IFN-γ) treatment and/or oxygen and glucose deprivation (OGD). The toxicity of these various paradigms was also measured. The expression of TRAIL, DR5, OPG, and mDcTRAILR2 was significantly increased after HI. In vitro, inflammatory cytokines and OGD treatment significantly induced mRNAs for TRAIL, DR5, OPG, and mDcTRAILR2 in primary neurons and of TRAIL and OPG in OPCs. TRAIL protein was expressed primarily in microglia and astroglia, whereas DR5 co-localized with neurons and OPCs in vivo. OGD enhanced TNF-α/IFN-γ toxicity in both neuronal and OPC cultures. Recombinant TRAIL exerted toxicity alone or in combination with OGD and TNF-α/IFN-γ in primary neurons but not in OPC cultures. The marked increases in the expression of TRAIL and its receptors after cytokine exposure and OGD in primary neurons and OPCs were similar to those found in our animal model of neonatal HI. The toxicity of TRAIL in primary neurons suggests that TRAIL signaling participates in neonatal brain injury after inflammation and HI.

Effects of electroacupuncture on apoptotic pathways in a rat model of focal cerebral ischemia

In this study, we investigated the molecular mechanisms underlying the anti-apoptotic properties of electroacupuncture (EA) in a rat model of middle cerebral artery occlusion (MCAO). Treatment with 2 Hz EA (1 mA) resulted in a markedly reduced infarct area after stroke, particularly in the middle region of the brain. Treatment with EA resulted in a significant decrease in the number of apoptotic cells identified by Hoechst 33342 and TUNEL staining. According to the results of the analysis for proteins involved in apoptosis, treatment with EA resulted in a significantly reduced expression of death receptor (DR)5. Among the members of the Bcl‑2 family, a higher expression of anti-apoptotic Bcl‑2 and Bcl‑xL was observed in the rats treated with EA, compared with the untreated rats with MCAO. As regards the expression of the inhibitor of apoptosis protein (IAP) family, a higher expression of anti-apoptotic cIAP‑1 and ‑2 was also detected in the cortex of the EA‑treated rats. Using western blot analysis, we observed that activated caspase‑3 was only significantly arrested by EA treatment in the rats with MCAO; however, according to the results of the caspase assay, the activities of caspase‑3, ‑8 and ‑9 were markedly inhibited by EA treatment. These results suggest that treatment with EA exerts anti‑apoptotic effects in cerebral ischemia in a rat model of MCAO and that these effects are associated with the inhibition of the DR and mitochondrial apoptotic pathways.

Immunological profile of silent brain infarction and lacunar stroke

Neuroinflammation is believed to be involved in the pathophysiological mechanisms of silent brain infarcts (SBI). However, the immunological profile of SBI has been scarcely investigated. In the context of a national research project named SILENCE, aimed at investigating clinical, biochemical and pathogenic features of SBI, we have measured the plasma profile of some inflammatory-related molecules in SBI patients (n = 21), patients with recent lacunar infarcts (LI, n = 28) and healthy controls (n = 31), consecutively enrolled in four Italian centres. A panel of chemokines (MIG, CTACK, IL16, SDF1a, MCP1), growth factors (SCF, SCGFb, HGF, IL3), immunoglobulin-type adhesion molecules (ICAM1, VCAM1), proinflammatory cytokines (IL18, INFa2, MIF, IL12p40), cell surface receptors on T-cells (IL2Ra), and inductors of apoptosis (TRAIL) was assessed in plasma samples by Luminex xMAP™ technology. Immunological parameters were compared using non-parametric statistics and performance to distinguish SBI and LI was evaluated by receiver operating characteristic (ROC) analysis. Plasma levels of ICAM1 were significantly higher in both SBI and LI patients as compared to controls (SBI≥LI>Ctrl). A different trend was observed for IL16 (SBI<LI>Ctrl), SCF (LI<SBI>Ctrl) and SCGFb (SBI>LI<Ctrl). SBI subjects had significantly increased levels of MIG when compared to controls (LI≤SBI>Ctrl) and IL18 when compared to LI patients (Ctrl≤SBI>LI). All the other immunological markers did not significantly differ among groups. According to ROC analysis, the best predictor for SBI condition was the chemokine MIG (AUC = 0.84, sensitivity 86%, specificity 77%), while SCF had the best performance in distinguishing LI patients (AUC = 0.84, sensitivity 86%, specificity 68%). These results confirm the involvement of inflammatory processes in cerebrovascular disorders, particularly in SBI, a very common age-related condition. The differences in plasma profile of inflammatory molecules may underlie different pathological mechanisms in SBI and LI patients.

Hypoxia-ischemia upregulates TRAIL and TRAIL receptors in the immature rat brain

The immature brain is susceptible to inflammatory injury induced by hypoxia-ischemia (HI) or infection, which causes serious neurodevelopmental disabilities in the survivors of preterm births. Recently, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its receptors (death receptor DR4/5 and decoy receptor DcR1/2) were reported to mediate various neuroinflammatory responses. However, little information is available regarding the role of TRAIL and its receptors in the immature brain after HI. The purpose of this study was to evaluate the expression of TRAIL and its receptors in the immature brain after HI and relate this expression to neurological function. We performed right common carotid artery ligation followed by hypoxia (6% O(2), 37°C) for 2.5 h to induce HI in postnatal day 3 rats. The distribution of TRAIL and its receptors, caspase-3 and CD68-labeled microglia/macrophages was evaluated 24 h after HI by immunostaining. The protein and mRNA expression of TRAIL and DR5 was measured by Western blot and real-time PCR, respectively. Delayed neuronal loss was evaluated by NeuN and Nissl staining 7 days after HI. Furthermore, neurological deficits were evaluated by a righting reflex test, time of eye opening and T-maze test. The expression of TRAIL, DR5 and DcR1/2 receptors and caspase-3 was more pronounced in the ipsilateral hemisphere compared with the contralateral part and the control group 24 h after HI. DR5/active caspase-3 double-positive cells were observed at 24 h after HI in the ipsilateral hemisphere but not in the contralateral hemisphere. The TRAIL and CD68 double-labeled cells were more pronounced in the ipsilateral cortical regions compared with the corresponding regions of the contralateral part. HI also resulted in a significant increase in TRAIL and DR5 protein and mRNA expression at 24 h, which corresponded to neuronal cell loss 7 days after HI. Furthermore, the HI group displayed impaired neurobehavioral development compared with the control group (p < 0.05). Altogether our results show that the TNF-α superfamily ligand TRAIL is induced on CD68+ microglia/macrophages after perinatal HI and that one of its receptors, DR5, is induced on neocortical neurons and glial cells. That many DR5+ cells were also caspase-3+ strongly supports the conclusion that these signaling molecules are involved in the delayed loss of neurons in the neocortex and in the neurobehavioral deficits that are often seen after perinatal HI.

Molecular mechanisms of neonatal brain injury

Fetal/neonatal brain injury is an important cause of neurological disability. Hypoxia-ischemia and excitotoxicity are considered important insults, and, in spite of their acute nature, brain injury develops over a protracted time period during the primary, secondary, and tertiary phases. The concept that most of the injury develops with a delay after the insult makes it possible to provide effective neuroprotective treatment after the insult. Indeed, hypothermia applied within 6 hours after birth in neonatal encephalopathy reduces neurological disability in clinical trials. In order to develop the next generation of treatment, we need to know more about the pathophysiological mechanism during the secondary and tertiary phases of injury. We review some of the critical molecular events related to mitochondrial dysfunction and apoptosis during the secondary phase and report some recent evidence that intervention may be feasible also days-weeks after the insult.

The immunology of stroke: from mechanisms to translation

Immunity and inflammation are key elements of the pathobiology of stroke, a devastating illness second only to cardiac ischemia as a cause of death worldwide. While the immune system participates in the brain damage produced by ischemia, the damaged brain, in turn, exerts a powerful immunosuppressive effect that promotes fatal intercurrent infections and threatens the survival of stroke patients. Inflammatory signaling is instrumental in all stages of the ischemic cascade, from the early damaging events triggered by arterial occlusion, to the late regenerative processes underlying post-ischemic tissue repair. Recent developments have revealed that stroke, like multiple sclerosis, engages both innate and adaptive immunity. But, unlike multiple sclerosis, adaptive immunity triggered by newly exposed brain antigens does not have an impact on the acute phase of the damage. Nevertheless, modulation of adaptive immunity exerts a remarkable protective effect on the ischemic brain and offers the prospect of new stroke therapies. However, immunomodulation is not devoid of deleterious side effects, and gaining a better understanding of the reciprocal interaction between the immune system and the ischemic brain is essential to harness the full therapeutic potential of the immunology of stroke.

The death-promoting molecule tumour necrosis factor-related apoptosis inducing ligand (TRAIL) is not required for the development of peripheral lymphopenia or granuloma necrosis during infection with virulent Mycobacterium avium

Disseminated infection with virulent Mycobacterium avium in C57Bl/6 (B6) mice leads to severe lymphocyte depletion in secondary lymphoid organs. In this study, we found an up-regulation of caspase-8 activity in spleen cell extracts from M. avium 25291-infected B6 mice compared to non-infected mice. The activation of this extrinsic apoptotic pathway correlated with an increase in inter-nucleosomal DNA fragmentation in CD4(+) spleen cells, as analysed by the terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay. These data suggest the involvement of death receptors in the induction of lymphocyte loss in the spleen, but previous work has excluded a role for tumour necrosis factor (TNF) receptors and Fas/CD95 in M. avium-induced lymphopenia. TNF-related apoptosis-inducing ligand (TRAIL) is expressed by different cell types of the immune system and induces apoptosis and killing of tumour cells while sparing normal cells. Here we used TRAIL(-/-) mice to determine if the absence of TRAIL prevented M. avium-induced immune pathology. We found that TRAIL-deficient mice still developed splenic lymphopenia during disseminated infection or granuloma necrosis during low-dose infections while exhibiting slightly increased susceptibility to M. avium 25291 when compared to B6 mice. However, in vivo proliferation of less virulent strains of M. avium was not influenced by TRAIL deficiency despite a decrease in interferon-γ production in infected B6.TRAIL(-/-) mice compared to B6 mice. Our results show that TRAIL does not play a significant role in either M. avium-induced pathology or protective immunity.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its death receptor (DR5) in Peyronie's disease. A biomolecular study of apoptosis activation

INTRODUCTION

Peyronie's disease (PD) is a connective tissue disorder of tunica albuginea (TA), a thick fibrous sheath surrounding the corpora cavernosa of the penis. Relatively, little is known about the disease itself.

AIM

To investigate whether the apoptosis cascade in degenerated and macroscopically deformed TA from men with PD is activated through the extrinsic pathway, by assessing the immunoexpression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its death receptor, DR5.

METHODS

TA plaques from 15 men with PD and from four unaffected men were processed for TRAIL and DR5 immunohistochemistry and Western blot analysis.

MAIN OUTCOME MEASURES

A greater understanding of the pathophysiology of PD through a molecular approach, to gain insights that may lead to novel forms of treatment.

RESULTS

Activation of the apoptosis mechanisms through the extrinsic pathway was demonstrated by TRAIL and DR5 overexpression in fibroblasts and myofibroblasts from affected TA.

CONCLUSION

The finding that apoptosis activation in TA plaques occurs, at least in part, via the extrinsic pathway may help devise novel therapeutic options for these patients.