Necrostatin-1 reduces histopathology and improves functional outcome after controlled cortical impact in mice

Necrostatin-1: a promising compound for neurological disorders

Necrostatin-1, a small molecular alkaloid, was identified as an inhibitor of necroptosis in 2005. Investigating the fundamental mechanism of Necrostatin-1 and its role in various diseases is of great significance for scientific and clinical research. Accumulating evidence suggests that Necrostatin-1 plays a crucial role in numerous neurological disorders. This review aims to provide a comprehensive overview of the potential functions of Necrostatin-1 in various neurological disorders, offering valuable insights for future research.

Regulated cell death in hypoxic-ischaemic encephalopathy: recent development and mechanistic overview

Hypoxic-ischaemic encephalopathy (HIE) in termed infants remains a significant cause of morbidity and mortality worldwide despite the introduction of therapeutic hypothermia. Depending on the cell type, cellular context, metabolic predisposition and insult severity, cell death in the injured immature brain can be highly heterogenous. A continuum of cell death exists in the H/I-injured immature brain. Aside from apoptosis, emerging evidence supports the pathological activation of necroptosis, pyroptosis and ferroptosis as alternative regulated cell death (RCD) in HIE to trigger neuroinflammation and metabolic disturbances in addition to cell loss. Upregulation of autophagy and mitophagy in HIE represents an intrinsic neuroprotective strategy. Molecular crosstalk between RCD pathways implies one RCD mechanism may compensate for the loss of function of another. Moreover, mitochondrion was identified as the signalling "hub" where different RCD pathways converge. The highly-orchestrated nature of RCD makes them promising therapeutic targets. Better understanding of RCD mechanisms and crosstalk between RCD subtypes likely shed light on novel therapy development for HIE. The identification of a potential RCD converging node may open up the opportunity for simultaneous and synergistic inhibition of cell death in the immature brain.

Electrical Stimulation Induces Activation of Mitochondrial Apoptotic Pathway and Down-Regulates Heat Shock Proteins in Pork: An Innovative Strategy for Enhancing the Ripening Process and Quality of Dry-Cured Loin Ham

A fundamental regulatory framework to elucidate the role of electrical stimulation (ES) in reducing long production cycles, enhancing protein utilization, and boosting product quality of dry-cured ham is essential. However, how mitochondria and enzymes in meat fibers are altered by ES during post-processing, curing, and fermentation procedures remains elusive. This study sought to explore the impact of ES on the regulation of heat shock proteins (HSP27, HSP70), apoptotic pathways, and subsequent influences on dry-cured pork loin quality. The gathered data validated the hypothesis that ES notably escalates mitochondrial oxidative stress and accelerates mitochondrial degradation along the ripening process. The proapoptotic response in ES-treated samples was increased by 120.7%, with a cellular apoptosis rate 5-fold higher than that in control samples. This mitochondrial degradation is marked by increased ratios of Bax/Bcl-2 protein along the time course, indicating that apoptosis could contribute to the dry-cured ham processing. ES was shown to further down-regulate HSP27 and HSP70, establishing a direct correlation with the activation of mitochondrial apoptosis pathways, accompanied by dry-cured ham quality improvements. The findings show that ES plays a crucial role in facilitating the ripening of dry-cured ham by inducing mitochondrial apoptosis to reduce HSP expression. This knowledge not only explains the fundamental mechanisms behind myofibril degradation in dry-cured ham production but also offers a promising approach to enhance quality and consistency.

An overview of preclinical models of traumatic brain injury (TBI): relevance to pathophysiological mechanisms

Background

Traumatic brain injury (TBI) is a major cause of morbidity and mortality, affecting millions annually worldwide. Although the majority of TBI patients return to premorbid baseline, a subset of patient can develop persistent and often debilitating neurocognitive and behavioral changes. The etiology of TBI within the clinical setting is inherently heterogenous, ranging from sport related injuries, fall related injuries and motor vehicle accidents in the civilian setting, to blast injuries in the military setting.

Objective

Animal models of TBI, offer the distinct advantage of controlling for injury modality, duration and severity. Furthermore, preclinical models of TBI have provided the necessary temporal opportunity to study the chronic neuropathological sequelae of TBI, including neurodegenerative sequelae such as tauopathy and neuroinflammation within the finite experimental timeline. Despite the high prevalence of TBI, there are currently no disease modifying regimen for TBI, and the current clinical treatments remain largely symptom based. The preclinical models have provided the necessary biological substrate to examine the disease modifying effect of various pharmacological agents and have imperative translational value.

Methods

The current review will include a comprehensive survey of well-established preclinical models, including classic preclinical models including weight drop, blast injury, fluid percussion injury, controlled cortical impact injury, as well as more novel injury models including closed-head impact model of engineered rotational acceleration (CHIMERA) models and closed-head projectile concussive impact model (PCI). In addition to rodent preclinical models, the review will include an overview of other species including large animal models and Drosophila.

Results

There are major neuropathological perturbations post TBI captured in various preclinical models, which include neuroinflammation, calcium dysregulation, tauopathy, mitochondrial dysfunction and oxidative stress, axonopathy, as well as glymphatic system disruption.

Conclusion

The preclinical models of TBI continue to offer valuable translational insight, as well as essential neurobiological basis to examine specific disease modifying therapeutic regimen.

Impact of Exercise Training on Survival Rate and Neural Cell Death in Sepsis Through the Maintenance of Redox Equilibrium

PURPOSE

Sepsis-related deaths occur during both the early proinflammatory and the late immunosuppressive phases of the condition. The balance of pro- and anti-inflammatory responses is influenced by damaged cells that die via either proinflammatory necroptosis or anti-inflammatory apoptosis. Both forms of cell death may be mediated by reactive oxygen species (ROS) generated during the proinflammatory response. Recent evidence suggests that exercise training boosts antioxidative capacity and could offer protection against sepsis. Given these findings, we aimed to examine the impact of exercise training on neural cell death in the context of sepsis.

METHODS

We assessed the effectiveness of exercise in reducing ROS production and the inflammatory response using a cecal ligation and puncture (CLP)-induced sepsis model. Forty C57BL/6N male mice were randomly divided into 2 groups: control (CLP-Con; n=20) and experimental (CLP-Ex; n=20). Before the induction of sepsis by CLP, the CLP-Ex mice underwent interval training on a treadmill 3 days per week for 8 weeks. Each day involved 10 cycles of 2 minutes at 8 m/min and 2 minutes at 15 m/min. After the CLP procedure, we monitored the survival of 10 mice from each group over a 30-hour period.

RESULTS

The findings indicated that exercise training increased the survival rate among mice with CLP-induced sepsis by enhancing antioxidative capacity and delaying the transition from a hyperdynamic to an immunosuppressive state.

CONCLUSION

Exercise training may delay the progression from the hyperdynamic state to the hypodynamic phase of sepsis by increasing antioxidant capacity and reducing apoptotic cell death.

Receptor-interacting protein 3-phosphorylated Ca2+ /calmodulin-dependent protein kinase II and mixed lineage kinase domain-like protein mediate intracerebral hemorrhage-induced neuronal necroptosis

Necroptosis-mediated cell death is an important mechanism in intracerebral hemorrhage (ICH)-induced secondary brain injury (SBI). Our previous study has demonstrated that receptor-interacting protein 1 (RIP1) mediated necroptosis in SBI after ICH. However, further mechanisms, such as the roles of receptor-interacting protein 3 (RIP3), mixed lineage kinase domain-like protein (MLKL), and Ca²⁺ /calmodulin-dependent protein kinase II (CaMK II), remain unclear. We hypothesized that RIP3, MLKL, and CaMK II might participate in necroptosis after ICH, including their phosphorylation. The ICH model was induced by autologous blood injection. First, we found the activation of necroptosis after ICH in brain tissues surrounding the hematoma (propidium iodide staining). Meanwhile, the phosphorylation and expression of RIP3, MLKL, and CaMK II were differently up-regulated (western blotting and immunofluorescent staining). The specific inhibitors could suppress RIP3, MLKL, and CaMK II (GSK'872 for RIP3, necrosulfonamide for MLKL, and KN-93 for CaMK II). We found the necroptosis surrounding the hematoma and the concrete interactions in RIP3-MLKL/RIP3-CaMK II also both decreased after the specific intervention (co-immunoprecipitation). Then we conducted the short-/long-term neurobehavioral tests, and the rats with specific inhibition mostly had better performance. We also found less blood-brain barrier (BBB) injury, and less neuron loss (Nissl staining) in intervention groups, which supported the neurobehavioral tests. Besides, oxidative stress and inflammation were also alleviated with intervention, which had significant less reactive oxygen species (ROS), tumor necrosis factor (TNF)-α, lactate dehydrogenase (LDH), Iba1, and GFAP surrounding the hematoma. These results confirmed that RIP3-phosphorylated MLKL and CaMK II participate in ICH-induced necroptosis and could provide potential targets for the treatment of ICH patients.

Outcomes of RIP Kinase Signaling During Neuroinvasive Viral Infection

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

Xenon attenuated neonatal lipopolysaccharide exposure induced neuronal necroptosis and subsequently improved cognition in juvenile rats

Background: Neonatal sepsis is known to cause neurodevelopment impairment and has been reported to increase risks for neurological/psychiatric disorders. In this study, we investigated the effect of xenon, a well-known potent neuroprotective gas, on neonatal sepsis-induced neurodevelopment impairment in rats together with underlying mechanism by focusing on receptor-interacting protein kinase (RIP) mediated neuronal necroptosis. Methods: 3-day-old Sprague-Dawley rat pups were exposed to either 70% xenon or N2 balanced with O2 for 6 h, during which lipopolysaccharide (LPS) was injected intraperitoneally for 3 times (500 μg/kg for the 1st and 250 μg/kg for the second and third dose; n = 6-10/group). In another cohort of 3-day-old rat pups, intracerebroventricular injection of necrostatin-1 (4 µg in 4 µl saline, a RIP-1-targeted inhibitor of necroptosis) was performed 20 min after the third dose of LPS. The learning ability and memory were assessed 25 days after LPS injection. Then, their hippocampus was collected for neuronal necroptosis with RIP and MIKL assessments using western blot and in situ immunostaining. Systemic and neuro-inflammation was also assessed. Results: LPS insult resulted in elevation of pro-inflammatory cytokine TNF-𝝰 and IL-6, caused neuronal necroptosis and damaged synaptic integrity at the brain developing stage, which finally led to the long-term cognitive impairment. Xenon inhibited necroptosis associated mediator RIP-1, RIP-3, and MLKL activation, protected neurons and attenuated cognitive dysfunction induced by LPS. Like xenon, the similar pattern changes induced by a RIP-1 inhibitor Necrostatin-1 were also found. Conclusion: This study indicates that necroptosis is involved in neonatal sepsis-induced neurofunctional impairments and xenon may be a novel therapeutic strategy to prevent/treat cognitive impairment in neonatal septic patients.

Fetuin-A alleviates neuroinflammation against traumatic brain injury-induced microglial necroptosis by regulating Nrf-2/HO-1 pathway

BACKGROUND

The microglia-mediated inflammatory response is a vital mechanism of secondary damage following traumatic brain injury (TBI), but the underlying mechanism of microglial activation is unclear.

METHODS

Controlled cortical impact (CCI) was induced in adult male C57BL/6J mice, and glutamate was used to construct a classical in vitro injury model in the primary microglia. Microglial activation was determined by western blot and immunostaining. The inflammatory factors were measured by enzyme-linked immunosorbent assay. The oxidative stress marker and mitochondrial reactive oxygen species (ROS) were measured by immunoblotting and MitoSox Red staining. Transmission electron microscopy was used to observe the typical morphology of necroptotic cells.

RESULTS

Our quantitative proteomics identified 2499 proteins; 157 were significantly differentially expressed in brain tissue between the 6 h after CCI (CCI6h) group and sham group, and 109 were significantly differentially expressed between the CCI24h and sham groups. Moreover, compared with the sham group, the terms "acute-phase response", "inflammation", and "protein binding" were significantly enriched in CCI groups. Fetuin-A, a liver-secreted acute-phase glycoprotein, was involved in these biological processes. Using an experimental TBI model, we found that the Fetuin-A level peaked at 6 h and then decreased gradually. Importantly, we showed that administration of Fetuin-A reduced the cortical lesion volume and edema area and inhibited the inflammatory response, which was associated with suppressing microglial necroptosis, thus decreasing microglial activation. Furthermore, administration of Fetuin-A attenuated mitochondrial oxidative stress in glutamate-treated microglial cells, which is a critical mechanism of necroptosis suppression. In addition, we demonstrated that Fetuin-A treatment promoted translocation of nuclear factor erythroid 2-related factor 2 (Nrf-2) from the cytoplasm to the nucleus in vivo; however, the Nrf-2 inhibitor ML385 and si-heme oxygenase-1 (si-HO-1) disrupted the regulation of oxidative stress by Fetuin-A and induced increased ROS levels and necroptosis in glutamate-treated microglial cells. Fetuin-A also protected neurons from adverse factors in vivo and in vitro.

CONCLUSIONS

Our results demonstrated that Fetuin-A activated Nrf-2/HO-1, suppressed oxidative stress and necroptosis levels, and thereby attenuates the abnormal inflammatory response following TBI. The findings suggest a potential therapeutic strategy for TBI treatment.

The role of regulatory necrosis in traumatic brain injury

Traumatic brain injury (TBI) is a major cause of death and disability in the population worldwide, of which key injury mechanism involving the death of nerve cells. Many recent studies have shown that regulatory necrosis is involved in the pathological process of TBI which includes necroptosis, pyroptosis, ferroptosis, parthanatos, and Cyclophilin D (CypD) mediated necrosis. Therefore, targeting the signaling pathways involved in regulatory necrosis may be an effective strategy to reduce the secondary injury after TBI. Meanwhile, drugs or genes are used as interference factors in various types of regulatory necrosis, so as to explore the potential treatment methods for the secondary injury after TBI. This review summarizes the current progress on regulatory necrosis in TBI.

Necroptosis Contributes to LPS-Induced Activation of the Hypothalamic-Pituitary-Adrenal Axis in a Piglet Model

Stressors cause activation of the hypothalamic-pituitary-adrenal (HPA) axis and a systemic inflammatory response. As a newly proposed cell death manner in recent years, necroptosis occurs in a variety of tissue damage and inflammation. However, the role of necroptosis in HPA axis activation remains to be elucidated. The aim of this study was to investigate the occurrence of necroptosis and its role in HPA activation in a porcine stress model induced by Escherichia coli lipopolysaccharide (LPS). Several typical stress behaviors like fever, anorexia, shivering and vomiting were observed in piglets after LPS injection. HPA axis was activated as shown by increased plasma cortisol concentration and mRNA expression of pituitary corticotropin-releasing hormone receptor 1 (CRHR1) and adrenal steroidogenic acute regulatory protein (StAR). The mRNA expression of tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β) and IL-6 in the hypothalamus, pituitary gland and adrenal gland was elevated by LPS, accompanied by the activation of necroptosis indicated by higher mRNA expression of necroptosis signals including receptor-interacting protein kinase (RIP) 1, RIP3, and phosphorylated mixed-lineage kinase domain-like protein (MLKL). Furthermore, necrostatin-1 (Nec-1), an inhibitor of necroptosis, inhibited necroptosis indicated by decreased mRNA levels of RIP1, RIP3, MLKL, and phosphoglycerate mutase family member 5 (PGAM5) in the hypothalamus, pituitary gland and adrenal gland. Nec-1 also decreased the mRNA expression of TNF-α and IL-β and inhibited the activation of the HPA axis indicated by lower plasma cortisol concentration and mRNA expression of adrenal type 2 melanocortin receptor (MC2R) and StAR. These findings suggest that necroptosis is present and contributes to HPA axis activation induced by LPS. These findings provide a potential possibility for necroptosis as an intervention target for alleviating HPA axis activation and stress responses.

Oxidative stress and mitochondrial dysfunction following traumatic brain injury: From mechanistic view to targeted therapeutic opportunities

Traumatic brain injury (TBI) is one of the most prevalent causes of permanent physical and cognitive disabilities. TBI pathology results from primary insults and a multi-mechanistic biochemical process, termed as secondary brain injury. Currently, there are no pharmacological agents for definitive treatment of patients with TBI. This article is presented with the purpose of reviewing molecular mechanisms of TBI pathology, as well as potential strategies and agents against pathological pathways. In this review article, materials were obtained by searching PubMed, Scopus, Elsevier, Web of Science, and Google Scholar. This search was considered without time limitation. Evidence indicates that oxidative stress and mitochondrial dysfunction are two key mediators of the secondary injury cascade in TBI pathology. TBI-induced oxidative damage results in the structural and functional impairments of cellular and subcellular components, such as mitochondria. Impairments of mitochondrial electron transfer chain and mitochondrial membrane potential result in a vicious cycle of free radical formation and cell apoptosis. The results of some preclinical and clinical studies, evaluating mitochondria-targeted therapies, such as mitochondria-targeted antioxidants and compounds with pleiotropic effects after TBI, are promising. As a proposed strategy in recent years, mitochondria-targeted multipotential therapy is a new hope, waiting to be confirmed. Moreover, based on the available findings, biologics, such as stem cell-based therapy and transplantation of mitochondria are novel potential strategies for the treatment of TBI; however, more studies are needed to clearly confirm the safety and efficacy of these strategies.

Necroptosis and Neuroinflammation in Retinal Degeneration

Necroptosis mediates the chronic inflammatory phenotype in neurodegeneration. Receptor-interacting protein kinase (RIPK) plays a pivotal role in the induction of necroptosis in various cell types, including microglia, and it is implicated in diverse neurodegenerative diseases in the central nervous system and the retina. Targeting RIPK has been proven beneficial for alleviating both neuroinflammation and degeneration in basic/preclinical studies. In this review, we discuss the role of necroptosis in retinal degeneration, including (1) the molecular pathways involving RIPK, (2) RIPK-dependent microglial activation and necroptosis, and (3) the interactions between necroptosis and retinal neuroinflammation/degeneration. This review will contribute to a renewed focus on neuroinflammation induced by necroptosis and to the development of anti-RIPK drugs against retinal degeneration.

Radiosynthesis and characterization of a carbon-11 PET tracer for receptor-interacting protein kinase 1

INTRODUCTION

Receptor-interacting protein kinase 1 (RIPK1) has emerged as a crucial regulator of necroptosis and the inflammatory response by activating a group of downstream immune receptors. It has been recognized as a pivotal contributor to cell death and inflammation in various physiological and pathological processes. RIPK1 deficiency or dysregulation in humans can cause severe immunodeficiency and neurodegenerative diseases such as multiple sclerosis and amyotrophic lateral sclerosis. Recently, diverse structures of RIPK1 inhibitors have been developed as potential therapeutics for neurodegenerative diseases and other pathological inflammatory processes. 7-oxo-2,4,5,7-tetrahydro-6H-pyrazolo[3,4-c]pyridine (Compound 5 or TZ7774) was reported as a novel RIPK1 inhibitor with a Ki of 0.91 nM that can suppress necroptosis in mouse and human cells. To develop a radiotracer for investigating the RIPK1 in vivo, we radiosynthesized [11C]TZ7774 and performed preliminary in vitro and in vivo evaluations in rodents and macaque.

METHODS

Synthesis of the desmethyl precursor TZ7790 was performed and optimized. The radiosynthesis of [11C]TZ7774 was achieved through TZ7790 reacting with [11C]methyl iodide via N-methylation. Ex vivo biodistribution of [11C]TZ7774 was performed in normal Sprague-Dawley rats. Characterization of [11C]TZ7774 in response to inflammation was performed using ex vivo biodistribution study in normal and LPS treated (10 mg/kg) C57BL/6 mice, and in vitro autoradiography and immunohistochemistry of the spleen. MicroPET brain study of [11C]TZ7774 in the macaque was also performed.

RESULTS AND CONCLUSIONS

The radiosynthesis of [11C]TZ7774 was achieved with good radiochemical yield (30-40%, decay corrected to the end of bombardment (EOB)), high chemical purity (>90%), high radiochemical purity (>99%), and high molar activity (>207 GBq/μmol, decay corrected to EOB). Biodistribution studies in Sprague-Dawley rats showed [11C]TZ7774 has a high brain uptake of 0.53 (%ID/g) at 5 min post injection; pancreas, spleen, kidney, and liver also showed a relatively high initial uptake of 0.49, 0.41, 0.62, and 0.95 at 5 min respectively. Uptake of [11C]TZ7774 increased in LPS-treated C57BL/6 mice by 40.9%, 90.4%, and 54.9% in liver, spleen, and kidney respectively. In vitro autoradiography study also revealed increased uptake of [11C]TZ7774 in the spleen of LPS-treated mice. Further characterization with immunohistochemistry confirmed increased expression of RIPK1 in red and white pulp of the spleen for mice pre-treated with LPS. MicroPET demonstrated that [11C]TZ7774 had good initial brain uptake in macaque with an (SUV) of ∼3.7 at 6-10 min, and quickly washed out from brain. These data confirm successful radiosynthesis of a RIPK1 specific radiotracer [11C]TZ7774. Our preliminary studies showed good response to LPS-induced inflammation in rodents and good uptake in macaque brain. [11C]TZ7774 has a potential to image RIPK1 related necroptosis and inflammatory processes.

Tetrahydrobiopterin in Cell Function and Death Mechanisms

Significance: Tetrahydrobiopterin (BH4) is most well known as a required cofactor for enzymes regulating cellular redox homeostasis, aromatic amino acid metabolism, and neurotransmitter synthesis. Less well known are the effects dependent on the cofactor's availability, factors governing its synthesis and recycling, redox implications of the cofactor itself, and protein-protein interactions that underlie cell death. This review provides an understanding of the recent advances implicating BH4 in the mechanisms of cell death and suggestions of possible therapeutic interventions. Recent Advances: The levels of BH4 often reflect the sum of synthetic and recycling enzyme activities. Enhanced expression of GTP cyclohydrolase, the rate-limiting enzyme in biosynthesis, increases BH4, leading to improved cell function and survival. Pharmacologically increasing BH4 levels has similar beneficial effects, leading to enhanced production of neurotransmitters and nitric oxide or reducing oxidant levels. The GTP cyclohydrolase-BH4 pairing has been implicated in a type of cell death, ferroptosis. At the cellular level, BH4 counteracts anticancer therapies directed to enhance ferroptosis via glutathione peroxidase 4 (GPX4) activity inhibition. Critical Issues: Because of the multitude of intertwined mechanisms, a clear relationship between BH4 and cell death is not well understood yet. The possibility that the cofactor directly influences cell viability has not been excluded in previous studies when modulating BH4-producing enzymes. Future Directions: The importance of cellular BH4 variations and BH4 biosynthetic enzymes to cell function and viability makes it essential to better characterize temporal changes, cofactor activity, and the influence on redox status, which in turn would help develop novel therapies. Antioxid. Redox Signal. 37, 171-183.

Silk Fibroin Hydrogels Could Be Therapeutic Biomaterials for Neurological Diseases

Silk fibroin, a natural macromolecular protein without physiological activity, has been widely used in different fields, such as the regeneration of bones, cartilage, nerves, and other tissues. Due to irrevocable neuronal injury, the treatment and prognosis of neurological diseases need to be investigated. Despite attempts to propel neuroprotective therapeutic approaches, numerous attempts to translate effective therapies for brain disease have been largely unsuccessful. As a good candidate for biomedical applications, hydrogels based on silk fibroin effectively amplify their advantages. The ability of nerve tissue regeneration, inflammation regulation, the slow release of drugs, antioxidative stress, regulation of cell death, and hemostasis could lead to a new approach to treating neurological disorders. In this review, we introduced the preparation of SF hydrogels and then delineated the probable mechanism of silk fibroin in the treatment of neurological diseases. Finally, we showed the application of silk fibroin in neurological diseases.

Necrostatin-1 Against Sevoflurane-Induced Cognitive Dysfunction Involves Activation of BDNF/TrkB Pathway and Inhibition of Necroptosis in Aged Rats

Postoperative cognitive dysfunction (POCD) induced by anesthesia or surgery has become a common complication in the aged population. Sevoflurane, a clinical inhalation anesthetic, could stimulate calcium overload and necroptosis to POCD. In addition, necroptosis inhibitor necrostatin-1 (Nec-1) alleviated cognitive impairment caused by multiple causes, including postoperative cognitive impairment. However, whether Nec-1 exerts a neuroprotective effect on POCD via calcium and necroptosis remains unclear. We anesthetized Sprague-Dawley rats with sevoflurane to construct the POCD model and to explore the mechanism underlying neuroprotective effects of Nec-1 in POCD. Rats were treated with Nec-1 (6.25 mg/kg) 1 h prior to anesthesia. Open field test and Morris water maze were employed to detect the cognitive function. In this study, rats exposed to sevoflurane displayed cognitive dysfunction without changes in spontaneous activity; however, the sevoflurane-induced POCD could be relieved by Nec-1 pretreatment. Nec-1 decreased sevoflurane-induced calcium overload and calpain activity in the hippocampus. In addition, Nec-1 alleviated the expression of p-RIPK1, RIPK1, p-RIPK3, RIPK3, p-MLKL and MLKL. Furthermore, Nec-1 remarkably increased BDNF and p-TrkB/TrkB expression in the hippocampus of aged rats. Ultimately, our research manifests evidence that Nec-1 may play a neuroprotective role against sevoflurane-induced cognitive impairment via the increase of BDNF/TrkB and suppression of necroptosis-related pathway.

Genetic inhibition of RIPK3 ameliorates functional outcome in controlled cortical impact independent of necroptosis

Traumatic brain injury (TBI) is a leading cause of death and disability with no specific effective therapy, in part because disease driving mechanisms remain to be elucidated. Receptor interacting protein kinases (RIPKs) are serine/threonine kinases that assemble multi-molecular complexes that induce apoptosis, necroptosis, inflammasome and nuclear factor kappa B activation. Prior studies using pharmacological inhibitors implicated necroptosis in the pathogenesis of TBI and stroke, but these studies cannot be used to conclusively demonstrate a role for necroptosis because of the possibility of off target effects. Using a model of cerebral contusion and RIPK3 and mixed lineage kinase like knockout (MLKL^-/-) mice, we found evidence for activation of RIPK3 and MLKL and assembly of a RIPK1-RIPK3-MLKL necrosome complex in pericontusional brain tissue. Phosphorylated forms of RIPK3 and MLKL were detected in endothelium, CD11b + immune cells, and neurons, and RIPK3 was upregulated and activated in three-dimensional human endothelial cell cultures subjected to CCI. RIPK3^-/- and MLKL^-/- mice had reduced blood-brain barrier damage at 24 h (p < 0.05), but no differences in neuronal death (6 h, p = ns in CA1, CA3 and DG), brain edema (24 h, p = ns), or lesion size (4 weeks, p = ns) after CCI. RIPK3^-/-, but not MLKL^-/- mice, were protected against postinjury motor and cognitive deficits at 1-4 weeks (RIPK3^-/- vs WT: p < 0.05 for group in wire grip, Morris water maze hidden platform trials, p < 0.05 for novel object recognition test, p < 0.01 for rotarod test). RIPK3^-/- mice had reduced infiltrating leukocytes (p < 0.05 vs WT in CD11b + cells, microglia and macrophages), HMGB1 release and interleukin-1 beta activation at 24-48 h (p < 0.01) after CCI. Our data indicate that RIPK3 contributes to functional outcome after cerebral contusion by mechanisms involving inflammation but independent of necroptosis.

Novel insights into RIPK1 as a promising target for future Alzheimer's disease treatment

Alzheimer's disease (AD) is an intractable neurodegenerative disease showing a clinical manifestation with memory loss, cognitive impairment and behavioral dysfunction. The predominant pathological characteristics of AD include neuronal loss, β-amyloid (Aβ) deposition and hyperphosphorylated Tau induced neurofibrillary tangles (NFTs), while considerable studies proved these could be triggered by neuronal death and neuroinflammation. Receptor-interacting protein kinase 1 (RIPK1) is a serine/threonine kinase existed at the cross-point of cell death and inflammatory signaling pathways. Emerging investigations have shed light on RIPK1 for its potential role in AD progression. The present review makes a bird's eye view on the functions of RIPK1 and mainly focus on the underlying linkages between RIPK1 and AD from comprehensive aspects including neuronal death, Aβ and Tau, inflammasome activation, BBB rupture, AMPK/mTOR, mitochondrial dysfunction and O-glcNAcylation. Moreover, the discovery of RIPK1 inhibitors, ongoing clinical trials along with future RIPK1-targeted therapeutics are also reviewed.

Inhibition of neuronal necroptosis mediated by RIP1/RIP3/MLKL provides neuroprotective effects on kaolin-induced hydrocephalus in mice

OBJECTIVES

Necroptosis is widespread in neurodegenerative diseases. Here, we examined necroptosis in the hippocampus and cortex after hydrocephalus and found that a necroptosis pathway inhibitor alleviates necroptosis and provides neuroprotective effects.

MATERIALS AND METHODS

Hydrocephalus was induced in C57BL/6 mice by kaolin. Haematoxylin and eosin (HE), Nissl, PI and Fluoro-Jade B (FJB) staining were used for general observations. Phosphorylated receptor-interacting protein kinase 3 (p-RIP3) and phosphorylated mixed lineage kinase domain-like (p-MLKL) were measured by Western blotting and immunohistochemistry. Scanning electron microscopy (SEM) was used to observe ependymal cilia. Magnetic resonance imaging (MRI) and the Morris water maze (MWM) test were used to assess neurobehavioral changes. Immunofluorescence was used to detect microglial and astrocyte activation. Inflammatory cytokines were measured by Western blotting and RT-PCR.

RESULTS

Obvious pathological changes appeared in the hippocampus and cortex after hydrocephalus, and expression of the necroptosis markers p-RIP3, p-MLKL and inflammatory cytokines increased. Necrostatin-1 (Nec-1) and GSK872 reduced necrotic cell death, attenuated p-RIP3 and p-MLKL levels, slightly improved neurobehaviours and inhibited microglial and astrocyte activation and inflammation.

CONCLUSIONS

RIP1/RIP3/MLKL mediates necroptosis in the cortex and hippocampus in a hydrocephalus mouse model, and Nec-1 and GSK872 have some neuroprotective effects.

Roadmap for Advancing Pre-Clinical Science in Traumatic Brain Injury

Pre-clinical models of disease have long played important roles in the advancement of new treatments. However, in traumatic brain injury (TBI), despite the availability of numerous model systems, translation from bench to bedside remains elusive. Integrating clinical relevance into pre-clinical model development is a critical step toward advancing therapies for TBI patients across the spectrum of injury severity. Pre-clinical models include in vivo and ex vivo animal work-both small and large-and in vitro modeling. The wide range of pre-clinical models reflect substantial attempts to replicate multiple aspects of TBI sequelae in humans. Although these models reveal multiple putative mechanisms underlying TBI pathophysiology, failures to translate these findings into successful clinical trials call into question the clinical relevance and applicability of the models. Here, we address the promises and pitfalls of pre-clinical models with the goal of evolving frameworks that will advance translational TBI research across models, injury types, and the heterogenous etiology of pathology.

Necroptosis: A Novel Pathway in Neuroinflammation

Neuroinflammation is a complex inflammatory process in the nervous system that is expected to play a significant role in neurological diseases. Necroptosis is a kind of necrosis that triggers innate immune responses by rupturing dead cells and releasing intracellular components; it can be caused by Toll-like receptor (TLR)-3 and TLR-4 agonists, tumor necrosis factor (TNF), certain microbial infections, and T cell receptors. Necroptosis signaling is modulated by receptor-interacting protein kinase (RIPK) 1 when the activity of caspase-8 becomes compromised. Activated death receptors (DRs) cause the activation of RIPK1 and the RIPK1 kinase activity-dependent formation of an RIPK1-RIPK3-mixed lineage kinase domain-like protein (MLKL), which is complex II. RIPK3 phosphorylates MLKL, ultimately leading to necrosis through plasma membrane disruption and cell lysis. Current studies suggest that necroptosis is associated with the pathogenesis of neuroinflammatory diseases, such as Alzheimer’s disease, Parkinson’s disease, and traumatic brain injury. Inhibitors of necroptosis, such as necrostatin-1 (Nec-1) and stable variant of Nec (Nec-1s), have been proven to be effective in many neurological diseases. The purpose of this article is to illuminate the mechanism underlying necroptosis and the important role that necroptosis plays in neuroinflammatory diseases. Overall, this article shows a potential therapeutic strategy in which targeting necroptotic factors may improve the pathological changes and clinical symptoms of neuroinflammatory disorders.

Celastrol protects against early brain injury after subarachnoid hemorrhage in rats through alleviating blood-brain barrier disruption and blocking necroptosis

BACKGROUND

Subarachnoid hemorrhage (SAH) is a life-threatening disease worldwide, and effective pharmaceutical treatment is still lacking. Celastrol is a plant-derived triterpene which showed neuroprotective potential in several types of brain insults. This study aimed to investigate the effects of celastrol on early brain injury (EBI) after SAH.

METHODS

A total of sixty-one male Sprague-Dawley rats were used in this study. Rat SAH endovascular perforation model was established to mimic the pathological changes of EBI after SAH. Multiple methods such as 3.0T MRI scanning, immunohistochemistry, western blotting and propidium iodide (PI) labeling were used to explore the therapeutic effects of celastrol on SAH.

RESULTS

Celastrol treatment attenuated SAH-caused brain swelling, reduced T2 lesion volume and ventricular volume in MRI scanning, and improved overall neurological score. Albumin leakage and the degradation of tight junction proteins were also ameliorated after celastrol administration. Celastrol protected blood-brain bairrer integrity through inhibiting MMP-9 expression and anti-neuroinflammatory effects. Additionally, necroptosis-related proteins RIP3 and MLKL were down-regulated and PI-positive cells in the basal cortex were less in the celastrol-treated SAH group than that in untreated SAH group.

CONCLUSIONS

Celastrol exhibits neuroprotective effects on EBI after SAH and deserves to be further investigated as an add-on pharmaceutical therapy.

Targeting Necrosis: Elastase-like Protease Inhibitors Curtail Necrotic Cell Death Both In Vitro and in Three In Vivo Disease Models

Necrosis is the main mode of cell death, which leads to multiple clinical conditions affecting hundreds of millions of people worldwide. Its molecular mechanisms are poorly understood, hampering therapeutics development. Here, we identify key proteolytic activities essential for necrosis using various biochemical approaches, enzymatic assays, medicinal chemistry, and siRNA library screening. These findings provide strategies to treat and prevent necrosis, including known medicines used for other indications, siRNAs, and establish a platform for the design of new inhibitory molecules. Indeed, inhibitors of these pathways demonstrated protective activity in vitro and in vivo in animal models of traumatic brain injury, acute myocardial infarction, and drug-induced liver toxicity. Consequently, this study may pave the way for the development of novel therapies for the treatment, inhibition, or prevention of a large number of hitherto untreatable diseases.

Dose-dependent effects of necrostatin-1 supplementation to tissue culture media of young porcine islets

Previous studies have shown that necrostatin-1 (Nec-1) supplementation improved the viability of murine islets following exposure to nitric oxide, increased the survival of human islets during hypoxic culture, and augmented the maturation of pre-weaned porcine islets (PPIs) after 7 days of tissue culture. A limitation of these studies is that only one concentration of Nec-1 was used, and no studies have determined the optimal dose of Nec-1 for PPIs. Thus, the present study examined the effects of Nec-1 on PPIs at four different doses—0, 25, 50, 100, and 200 μM—after 7 days of tissue culture when supplemented on day 3. PPIs were isolated from pancreata of pre-weaned Yorkshire piglets (8–15 days old) and cultured in a specific islet maturation media added with Nec-1 on day 3 of tissue culture at 4 different doses—0, 25, 50, 100, and 200 μM (n = 6 for each dose). After 7 days of tissue culture, islets were assessed for recovery, viability, endocrine cellular content, GLUT2 expression in beta cells, and insulin secretion after glucose challenge. Nec-1 did not affect the viability of both intact islets and dissociated islets cells during tissue culture regardless of doses. Islets cultured in media supplemented with Nec-1 at 100 μM, but not 25, 50, or 200 μM, had a significantly higher recovery, composition of endocrine cells, GLUT2 expression in beta cells, and insulin secretion capacity than control islets cultured in media without Nec-1 supplementation. Moreover, culturing islets in 200 μM Nec-1 supplemented media not only failed to improve the insulin release but resulted in a lower glucose-induced insulin stimulation index compared to islets cultured in media added with 100 μM Nec-1. Xenotransplantation using porcine islets continues to demonstrate scientific advances to justify this area of research. Our findings indicate that Nec-1 supplementation at 100 μM was most effective to enhance the in vitro maturation of PPIs during tissue culture.

The molecular mechanisms of MLKL-dependent and MLKL-independent necrosis

Necrosis, a type of unwanted and passive cell demise, usually occurs under the excessive external stress and is considered to be unregulated. However, under some special conditions such as caspase inhibition, necrosis is regulable in a well-orchestrated way. The term 'regulated necrosis' has been proposed to describe such programed necrosis. Recently, several forms of necrosis, including necroptosis, pyroptosis, ferroptosis, parthanatos, oxytosis, NETosis, and Na+/K+-ATPase-mediated necrosis, have been identified, and some crucial regulators governing regulated necrosis have also been discovered. Mixed lineage kinase domain-like pseudokinase (MLKL), a core regulator in necroptosis, acts as an executioner in response to ligands of death receptor family. Its activation requires the receptor-interacting protein kinases, RIP1 and RIP3. However, MLKL is only involved in necroptosis, i.e. MLKL is dispensable for necrosis. Therefore, this review is aimed at summarizing the molecular mechanisms of MLKL-dependent and MLKL-independent necrosis.

Receptor-interacting protein kinase 1 (RIPK1) as a therapeutic target

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) is a key mediator of cell death and inflammation. The unique hydrophobic pocket in the allosteric regulatory domain of RIPK1 has enabled the development of highly selective small-molecule inhibitors of its kinase activity, which have demonstrated safety in preclinical models and clinical trials. Potential applications of these RIPK1 inhibitors for the treatment of monogenic and polygenic autoimmune, inflammatory, neurodegenerative, ischaemic and acute conditions, such as sepsis, are emerging. This article reviews RIPK1 biology and disease-associated mutations in RIPK1 signalling pathways, highlighting clinical trials of RIPK1 inhibitors and potential strategies to mitigate development challenges.

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) — a key mediator of cell death and inflammation — is activated in human diseases. Here, Yuan and colleagues discuss current understanding of RIPK1 biology and its association with diseases including inflammatory and autoimmune disorders, neurodegenerative diseases and sepsis. The clinical development of small-molecule RIPK1 inhibitors and associated challenges are discussed.

Up-regulation of CHMP4B alleviates microglial necroptosis induced by traumatic brain injury

Microglial cells are key component of central nervous system (CNS) and mediate the immune response of the brain under physiological or pathological conditions. It tends to activate into a pro‐inflammatory M1 phenotype after traumatic brain injury (TBI) and promote secondary brain damage. Recently, necroptosis was found to promote microglial activation and neuroinflammation after TBI. However, the mechanism and specific interventions of microglial necroptosis after TBI remain poorly investigated. Here, we reported that overexpress the charged multivesicular body protein 4b (CHMP4B) which is a core member of the endosomal sorting required for transport complex III (ESCRT‐III) significantly decreased the level of necroptosis in microglia, improved neurological function recovery and protected against cell death after TBI. Further investigation showed that forkhead transcription factor O1 (FOXO1) was a crucial transcription factor that increased CHMP4B transcription by binding to the promoter region, thereby inhibiting necroptosis in microglia. Collectively, our findings demonstrated that CHMP4B relieved microglial necroptosis and neuroinflammation after TBI, and promote the recovery of nerve function. FOXO1 is an important factor in promoting CHMP4B expression. This study provides the novel viewpoint for TBI prevention and treatment.

Changes in Expression of Receptor-Interacting Protein Kinase 1 in Secondary Neural Tissue Damage Following Spinal Cord Injury

Introduction:

Necroptosis is a form of programmed cell death that is different from apoptotic cell death. Receptor-interacting protein kinase 1 (RIPK1) plays a particularly important function in necroptosis execution. This study investigated changes in expression of RIPK1 in secondary neural tissue damage following spinal cord injury in mice. The time course of the RIPK1 expression was also compared with that of apoptotic cell death in the lesion site.

Methods and Materials:

Immunostaining for RIPK1 was performed at different time points after spinal cord injury. The protein expressions of RIPK1 were determined by western blot. The RIPK1 expressions in various neural cells were investigated using immunohistochemistry. To investigate the time course of apoptotic cell death, TUNEL-positive cells were counted at the different time points. To compare the incidence of necroptosis and apoptosis, the RIPK1-labeled sections were co-stained with TUNEL.

Results:

The RIPK1 expression was significantly upregulated in the injured spinal cord. The upregulation of RIPK1 expression was observed in neurons, astrocytes, and oligodendrocytes. The increase in RIPK1 expression started at 4 hours and peaked at 3 days after injury. Time course of the RIPK1 expression was similar to that of apoptosis detected by TUNEL. Interestingly, the increased expression of RIPK1 was rarely observed in the TUNEL-positive cells. Furthermore, the number of RIPK1-positive cells was significantly higher than that of TUNEL-positive cells.

Conclusions:

This study demonstrated that the expression of RIPK1 increased in various neural cells and peaked at 3 days following spinal cord injury. The temporal change of the RIPK1 expression was analogous to that of apoptosis at the lesion site. However, the increase in RIPK1 expression was barely seen in the apoptotic cells. These findings suggested that the RIPK1 might contribute to the pathological mechanism of the secondary neural tissue damage after spinal cord injury.

Assessment of necroptosis in the retina in a repeated primary ocular blast injury mouse model

Primary blast injury (caused by the initial rapid increase in pressure following an explosive blast) to the retina and optic nerve (ON) causes progressive visual loss and neurodegeneration. Military personnel are exposed to multiple low-overpressure blast waves, which may be in quick succession, such as during breacher training or in combat. We investigated the necroptotic cell death pathway in the retina in a mouse repeated primary ocular blast injury (rPBI) model using immunohistochemistry. We further evaluated whether intravitreal injections of a potent necroptosis inhibitor, Necrostatin-1s (Nec-1s), protects the retina and ON axons by retinal ganglion cells (RGC) counts, ON axonal counting and optical coherence tomography (OCT) analysis of vitreous haze. Receptor interacting protein kinase (RIPK) 3, increased in the inner plexiform layer 2 days post injury (dpi) and persisted until 14 dpi, whilst RIPK1 protein expression did not change after injury. The number of degenerating ON axons was increased at 28 dpi but there was no evidence of a reduction in the number of intact ON axons or RNA-binding protein with multiple splicing (RBPMS)⁺ RGC in the retina by 28 dpi in animals not receiving any intravitreal injections. But, when intravitreal injections (vehicle or Nec-1s) were given there was a significant reduction in RBPMS⁺ RGC numbers, suggesting that rPBI with intraocular injections is damaging to RGC. There were fewer RGC lost after Nec-1s than vehicle injection, but there was no effect of Nec-1s or vehicle treatment on the number of degenerating axons. OCT analysis demonstrated no effect of rPBI on vitreous haze, but intravitreal injection combined with rPBI increased vitreous haze (P = 0.004). Whilst necroptosis may be an active cell death signalling pathway after rPBI, its inhibition did not prevent cell death, and intravitreal injections in combination with rPBI increased vitreous inflammation and reduced RBPMS⁺ RGC numbers, implying intravitreal injection is not an ideal method for drug delivery after rPBI.

Modeling Controlled Cortical Impact Injury in 3D Brain-Like Tissue Cultures

Traumatic brain injury (TBI) survivors suffer long term from mental illness, neurodegeneration, and neuroinflammation. Studies of 3D tissue models have provided new insights into the pathobiology of many brain diseases. Here, a 3D in vitro contusion model is developed consisting of mouse cortical neurons grown on a silk scaffold embedded in collagen and used outcomes from an in vivo model for benchmarking. Molecular, cellular, and network events are characterized in response to controlled cortical impact (CCI). In this model, CCI induces degradation of neural network structure and function and release of glutamate, which are associated with the expression of programmed necrosis marker phosphorylated Mixed Lineage Kinase Domain Like Pseudokinase (pMLKL). Neurodegeneration is observed first in the directly impacted area and it subsequently spreads over time in 3D space. CCI reduces phosphorylated protein kinase B (pAKT) and Glycogen synthase kinase 3 beta (GSK3β) in neurons in vitro and in vivo, but discordant responses are observed in phosphprylated ribosomal S6 kinase (pS6) and phosphorylated Tau (pTau) expression. In summary, the 3D brain-like culture system mimicked many aspects of in vivo responses to CCI, providing evidence that the model can be used to study the molecular, cellular, and functional sequelae of TBI, opening up new possibilities for discovery of therapeutics.

The necroptosis pathway and its role in age-related neurodegenerative diseases: will it open up new therapeutic avenues in the next decade?

INTRODUCTION

Necroptosis is a programmed form of necrotic cell death. Growing evidence demonstrates that necroptosis contributes to cell demise in different pathological conditions including age-dependent neurodegenerative diseases (NDs). These findings open new avenues for understanding the mechanisms of neuronal loss in NDs, which might eventually translate into novel therapeutic interventions.

AREAS COVERED

We reviewed key aspects of necroptosis, in health and disease, focusing on evidence demonstrating its involvement in the pathogenesis of age-related NDs. We then highlight the activation of this pathway in the mechanism of axonal degeneration. We searched on PubMed the literature regarding necroptosis published between 2008 and 2020 and reviewed all publications were necroptosis was studied in the context of age-related NDs.

EXPERT OPINION

Axonal loss and neuronal death are the ultimate consequences of NDs that translate into disease phenotypes. Targeting degenerative mechanisms of the neuron appears as a strategy that might cover a wide range of diseases. Thus, the participation of necroptosis as a common mediator of neuronal demise emerges as a promising target for therapeutic intervention. Considering evidence demonstrating that necroptosis mediates axonal degeneration, we propose and discuss the potential of targeting necroptosis-mediated axonal destruction as a strategy to tackle NDs before neuronal loss occurs.

Optimal concentration of necrostatin-1 for protecting against hippocampal neuronal damage in mice with status epilepticus

Hippocampal neurons undergo various forms of cell death after status epilepticus. Necrostatin-1 specifically inhibits necroptosis mediated by receptor interacting protein kinase 1 (RIP1) and RIP3 receptors. However, there are no reports of necroptosis in mouse models of status epilepticus. Therefore, in this study, we investigated the effects of necrostatin-1 on hippocampal neurons in mice with status epilepticus, and, furthermore, we tested different amounts of the compound to identify the optimal concentration for inhibiting necroptosis and apoptosis. A mouse model of status epilepticus was produced by intraperitoneal injection of kainic acid, 12 mg/kg. Different concentrations of necrostatin-1 (10, 20, 40, and 80 μM) were administered into the lateral ventricle 15 minutes before kainic acid injection. Hippocampal damage was assessed by hematoxylin-eosin staining 24 hours after the model was successfully produced. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining, western blot assay and immunohistochemistry were used to evaluate the expression of apoptosis-related and necroptosis-related proteins. Necrostatin-1 alleviated damage to hippocampal tissue in the mouse model of epilepsy. The 40 μM concentration of necrostatin-1 significantly decreased the number of apoptotic cells in the hippocampal CA1 region. Furthermore, necrostatin-1 significantly downregulated necroptosis-related proteins (MLKL, RIP1, and RIP3) and apoptosis-related proteins (cleaved-Caspase-3, Bax), and it upregulated the expression of anti-apoptotic protein Bcl-2. Taken together, our findings show that necrostatin-1 effectively inhibits necroptosis and apoptosis in mice with status epilepticus, with the 40 μM concentration of the compound having an optimal effect. The experiments were approved by the Animal Ethics Committee of Fujian Medical University, China (approval No. 2016-032) on November 9, 2016.

Necrostatin-1 prevents the proapoptotic protein Bcl-2/adenovirus E1B 19-kDa interacting protein 3 from integration into mitochondria

Necrostatin-1 (Nec-1) has previously been shown to protect neurons from death in traumatic and ischemic brain injuries. This study tests the hypothesis that Nec-1 protects neural cells against traumatic and ischemic brain injuries through inhibition of the Bcl-2/adenovirus E1B 19-kDa interacting protein 3 (BNIP3). We have used biochemical and morphological techniques to determine the inhibition of Nec-1 on BNIP3-induced cell death and to identify its mechanism of action in in vivo and in vitro models of neurodegeneration. Here we show that Nec-1 significantly increased neuronal viability following prolonged exposure to hypoxia in vitro, and attenuated myelin damage and neuronal death in traumatic brain injury and cerebral ischemia in Sprague-Dawley rats. Nec-1 alleviated traumatic brain injury-induced up-regulation of BNIP3 in mature oligodendrocytes. In isolated mitochondria, Nec-1 prevented BNIP3 from integrating into mitochondria by modifying its binding sites on the mitochondria. Consequently, Nec-1 robustly inhibited BNIP3-induced collapse of mitochondrial membrane potential and reduced the opening probability of mitochondrial permeability transition pores. Nec-1 also preserved mitochondrial ultrastructure and suppressed BNIP3-induced nuclear translocation of apoptosis-inducing factor. In conclusion, Nec-1 protects neurons and oligodendrocytes against traumatic and ischemic brain injuries by targeting the BNIP3-induced cell death pathway, and is a novel inhibitor for BNIP3. Cover Image for this issue: https://doi.org/10.1111/jnc.15056.

Necroptosis, ADAM proteases and intestinal (dys)function

Recently, an unexpected connection between necroptosis and members of the a disintegrin and metalloproteinase (ADAM) protease family has been reported. Necroptosis represents an important cell death routine which helps to protect from viral, bacterial, fungal and parasitic infections, maintains adult T cell homeostasis and contributes to the elimination of potentially defective organisms before parturition. Equally important for organismal homeostasis, ADAM proteases control cellular processes such as development and differentiation, immune responses or tissue regeneration. Notably, necroptosis as well as ADAM proteases have been implicated in the control of inflammatory responses in the intestine. In this review, we therefore provide an overview of the physiology and pathophysiology of necroptosis, ADAM proteases and intestinal (dys)function, discuss the contribution of necroptosis and ADAMs to intestinal (dys)function, and review the current knowledge on the role of ADAMs in necroptotic signaling.

Molecular mechanisms of necroptosis and relevance for neurodegenerative diseases

Necroptosis is a regulated cell death pathway morphologically similar to necrosis that depends on the kinase activity of receptor interacting protein 3 (RIP3) and the subsequent activation of the pseudokinase mixed lineage kinase domain-like protein (MLKL), being also generally dependent on RIP1 kinase activity. Necroptosis can be recruited during pathological conditions, usually following the activation of death receptors under specific cellular contexts. In this regard, necroptosis has been implicated in the pathogenesis of multiple disorders, including acute and chronic neurodegenerative diseases, such as Parkinson's and Alzheimer's diseases, and multiple sclerosis. Here, we summarize the molecular mechanisms regulating the induction of necroptosis and downstream effectors of this form of cell death, besides exploring non-necroptotic roles for necroptosis-related proteins that may impact on alternative cell death pathways and inflammatory mechanisms in disease. Finally, we outline the recent evidence implicating necroptosis in neurodegenerative conditions and the emerging therapeutic perspectives targeting necroptosis in these diseases.

Arc silence aggravates traumatic neuronal injury via mGluR1-mediated ER stress and necroptosis

Delayed neuronal death is associated with neurological deficits and mortality after traumatic brain injury (TBI), where post-synaptic density (PSD) proteins are thought to play key roles. The immediate-early gene (IEG) coded protein Arc is a brain-specific PSD protein that controls synaptic plasticity and learning behaviors. In this study, we investigated the expression and biological function of Arc in neuronal death after TBI in an in vitro model mimicked by traumatic neuronal injury (TNI) in cortical neurons. TNI caused a temporal increase of Arc expression at 3 and 6 h. Knockdown of Arc expression using small interfering RNA (Si-Arc-3) promoted TNI-induced cytotoxicity and apoptosis. The results of western blot showed that Si-Arc-3 transfection further enhanced the activation of endoplasmic reticulum (ER) stress-associated factors, including glucose-regulated protein 78 (GRP78), C/EBP homologous protein (CHOP) and caspase-12 after TNI. In addition, knockdown of Arc significantly increased expression of (receptor-interacting protein kinase 1) RIP1 and the number of necroptotic cells, which were apparently prevented by necrostatin-1 (Nec-1). The results of immunostaining and western blot showed that knockdown of Arc activated the metabotropic glutamate receptor 1 (mGluR1) and intracellular Ca²⁺ release in neurons. Mechanistically, the Si-Arc-3-induced activation of ER stress-associated factors, RIP1 expression, apoptosis, and necroptosis were partially reversed by the mGluR1 antagonist AIDA. In summary, our data suggest that silence of Arc expression aggravates neuronal death after TNI by promoting apoptosis and necroptosis. These data support for the first time that Arc may represent a novel candidate for therapies against TBI.

The Function and Mechanisms of Autophagy in Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the most common causes of long-term disability and death worldwide. Autophagy is activated and autophagic flux is impaired following TBI. But the controversial roles and underlying mechanisms of autophagy after TBI are not clear. This chapter will update the current state of knowledge in the process of autophagy, the roles of autophagy in TBI as well as some upstream moleculars and pharmacological regulators of autophagy involved in TBI. We also discuss autophagy mechanism-based preclinical pharmacological intervention. These observations make autophagy an attractive therapeutic target for developing new therapeutic strategies to achieve better outcomes for patients suffering from TBI.

Necroptosis and RIPK1-mediated neuroinflammation in CNS diseases

Apoptosis is crucial for the normal development of the nervous system, whereas neurons in the adult CNS are relatively resistant to this form of cell death. However, under pathological conditions, upregulation of death receptor family ligands, such as tumour necrosis factor (TNF), can sensitize cells in the CNS to apoptosis and a form of regulated necrotic cell death known as necroptosis that is mediated by receptor-interacting protein kinase 1 (RIPK1), RIPK3 and mixed lineage kinase domain-like protein (MLKL). Necroptosis promotes further cell death and neuroinflammation in the pathogenesis of several neurodegenerative diseases, including multiple sclerosis, amyotrophic lateral sclerosis, Parkinson disease and Alzheimer disease. In this Review, we outline the evidence implicating necroptosis in these neurological diseases and suggest that targeting RIPK1 might help to inhibit multiple cell death pathways and ameliorate neuroinflammation.

B-RAFV600E Inhibitor Dabrafenib Attenuates RIPK3-Mediated Necroptosis and Promotes Functional Recovery after Spinal Cord Injury

The receptor-interacting protein kinase 3 (RIPK3) is a key regulator of necroptosis and is involved in various pathologies of human diseases. We previously reported that RIPK3 expression is upregulated in various neural cells at the lesions and necroptosis contributed to secondary neural tissue damage after spinal cord injury (SCI). Interestingly, recent studies have shown that the B-RAF^V600E inhibitor dabrafenib has a function to selectively inhibit RIPK3 and prevents necroptosis in various disease models. In the present study, using a mouse model of thoracic spinal cord contusion injury, we demonstrate that dabrafenib administration in the acute phase significantly inhibites RIPK3-mediated necroptosis in the injured spinal cord. The administration of dabrafenib attenuated secondary neural tissue damage, such as demyelination, neuronal loss, and axonal damage, following SCI. Importantly, the neuroprotective effect of dabrafenib dramatically improved the recovery of locomotor and sensory functions after SCI. Furthermore, the electrophysiological assessment of the injured spinal cord objectively confirmed that the functional recovery was enhanced by dabrafenib. These findings suggest that the B-RAF^V600E inhibitor dabrafenib attenuates RIPK3-mediated necroptosis to provide a neuroprotective effect and promotes functional recovery after SCI. The administration of dabrafenib may be a novel therapeutic strategy for treating patients with SCI in the future.

Retinal Ganglion Cells Die by Necroptotic Mechanisms in a Site-Specific Manner in a Rat Blunt Ocular Injury Model

Closed-globe injury can cause visual loss in military and civilian populations, with retinal cell death, including retinal ganglion cell (RGC) degeneration, leading to irreversible blindness. RGC and optic nerve (ON) degeneration after eye or head injury is termed traumatic optic neuropathy (TON). There are currently no treatments for RGC loss, therefore novel therapeutics to prevent RGC death or promote axonal regeneration are a priority. We investigated necroptotic signaling mechanisms in a rat blunt ocular injury model. After bilateral blunt trauma, protein expression and retinal localization of necroptosis pathway members (receptor interacting protein kinase 1, RIPK1; receptor interacting protein kinase 3, RIPK3; and mixed lineage kinase domain like pseudokinase, MLKL) were assessed by Western blot and immunohistochemistry (IHC), and potent necroptosis inhibitor Necrostatin-1s (Nec-1s) was delivered by intravitreal injection to one eye and vehicle to the contralateral eye. RGC and photoreceptor survival were assessed by cell counting and outer nuclear layer (ONL) thickness measurements on histology. The neuroprotective effects of Nec-1s were assessed in primary retinal culture by βIII-tubulin⁺ RGC cell counts. MLKL protein expression were upregulated at 48 h after injury and MLKL immunolocalised to retinal binding protein with multiple splice (RBPMS)⁺ RGC, inner nuclear cells and ONL cells, specifically at the retinal injury site. RIPK3 expression did not increase but RIPK3 co-immunolocalised with RBPMS⁺ RGC in intact and injured retinae. In vitro, a Nec-1s concentration of 0.01 pg/µL was RGC neuroprotective. In the blunt ocular injury rat model, Nec-1s prevented RGC death at the center of the impact site but did not protect against ONL thinning or provide functional restitution. RGC degeneration in our blunt ocular injury model is site-specific, with necroptosis driving death at the center of the focal impact site.

The Neuroprotective Effects of Necrostatin-1 on Subarachnoid Hemorrhage in Rats Are Possibly Mediated by Preventing Blood-Brain Barrier Disruption and RIP3-Mediated Necroptosis

Despite the substantial efforts to elucidate the role of early brain injury in subarachnoid hemorrhage (SAH), an effective pharmaceutical therapy for patients with SAH continues to be unavailable. This study aims to reveal the role of necroptosis after SAH, and explore whether the disruption of the blood-brain barrier (BBB) and RIP3-mediated necroptosis following SAH in a rat SAH model are altered by necrostatin-1 via its selective inhibition of receptor-interacting protein kinase 1 (RIP1). Sixty-five rats were used in the experiments. The SAH model was established using endovascular perforation. Necrostatin-1 was intracerebroventricularly injected 1 h before SAH induction. The neuroprotective effects of necrostatin-1 were evaluated with multiple methods such as magnetic resonance imaging (MRI) scanning, immunohistochemistry, propidium iodide (PI) labeling, and western blotting. Pretreatment with necrostatin-1 attenuated brain swelling and reduced the lesion volume on T2 sequence and ventricular volume on MRI 72 h after SAH induction. Albumin leakage and the degradation of tight junction proteins were also ameliorated by necrostatin-1 administration. In addition, necrostatin-1 decreased the number of PI-positive cells in the basal cortex, reduced the levels of the RIP3 and MLKL proteins, and inhibited the production of the pro-inflammatory cytokines IL-1β, IL-6, and TNF-α. Based on the findings from the present study, the selective RIP1 inhibitor necrostatin-1 functioned as a neuroprotective agent after SAH by attenuating brain swelling and BBB disruption. Moreover, the necrostatin-1 pretreatment prevented SAH-induced necroptosis by suppressing the activity of the RIP3/MLKL signaling pathway. These results will provide insights into new drugs and pharmacological targets to manage SAH, which are worth further study.

Blood-Related Toxicity after Traumatic Brain Injury: Potential Targets for Neuroprotection

Emergency visits, hospitalizations, and deaths due to traumatic brain injury (TBI) have increased significantly over the past few decades. While the primary early brain trauma is highly deleterious to the brain, the secondary injury post-TBI is postulated to significantly impact mortality. The presence of blood, particularly hemoglobin, and its breakdown products and key binding proteins and receptors modulating their clearance may contribute significantly to toxicity. Heme, hemin, and iron, for example, cause membrane lipid peroxidation, generate reactive oxygen species, and sensitize cells to noxious stimuli resulting in edema, cell death, and increased morbidity and mortality. A wide range of other mechanisms such as the immune system play pivotal roles in mediating secondary injury. Effective scavenging of all of these pro-oxidant and pro-inflammatory metabolites as well as controlling maladaptive immune responses is essential for limiting toxicity and secondary injury. Hemoglobin metabolism is mediated by key molecules such as haptoglobin, heme oxygenase, hemopexin, and ferritin. Genetic variability and dysfunction affecting these pathways (e.g., haptoglobin and heme oxygenase expression) have been implicated in the difference in susceptibility of individual patients to toxicity and may be target pathways for potential therapeutic interventions in TBI. Ongoing collaborative efforts are required to decipher the complexities of blood-related toxicity in TBI with an overarching goal of providing effective treatment options to all patients with TBI.

The necroptosis machinery mediates axonal degeneration in a model of Parkinson disease

Parkinson's disease (PD) is the second most common neurodegenerative condition, characterized by motor impairment due to the progressive degeneration of dopaminergic neurons in the substantia nigra and depletion of dopamine release in the striatum. Accumulating evidence suggest that degeneration of axons is an early event in the disease, involving destruction programs that are independent of the survival of the cell soma. Necroptosis, a programmed cell death process, is emerging as a mediator of neuronal loss in models of neurodegenerative diseases. Here, we demonstrate activation of necroptosis in postmortem brain tissue from PD patients and in a toxin-based mouse model of the disease. Inhibition of key components of the necroptotic pathway resulted in a significant delay of 6-hydroxydopamine-dependent axonal degeneration of dopaminergic and cortical neurons in vitro. Genetic ablation of necroptosis mediators MLKL and RIPK3, as well as pharmacological inhibition of RIPK1 in preclinical models of PD, decreased dopaminergic neuron degeneration, improving motor performance. Together, these findings suggest that axonal degeneration in PD is mediated by the necroptosis machinery, a process here referred to as necroaxoptosis, a druggable pathway to target dopaminergic neuronal loss.

Tissue-regenerative potential of the secretome of γ-irradiated peripheral blood mononuclear cells is mediated via TNFRSF1B-induced necroptosis

Peripheral blood mononuclear cells (PBMCs) have been shown to produce and release a plethora of pro-angiogenetic factors in response to γ-irradiation, partially accounting for their tissue-regenerative capacity. Here, we investigated whether a certain cell subtype of PBMCs is responsible for this effect, and whether the type of cell death affects the pro-angiogenic potential of bioactive molecules released by γ-irradiated PBMCs. PBMCs and PBMC subpopulations, including CD4⁺ and CD8⁺ T cells, B cells, monocytes, and natural killer cells, were isolated and subjected to high-dose γ-irradiation. Transcriptome analysis revealed subpopulation-specific responses to γ-irradiation with distinct activation of pro-angiogenic pathways, cytokine production, and death receptor signalling. Analysis of the proteins released showed that interactions of the subsets are important for the generation of a pro-angiogenic secretome. This result was confirmed at the functional level by the finding that the secretome of γ-irradiated PBMCs displayed higher pro-angiogenic activity in an aortic ring assay. Scanning electron microscopy and image stream analysis of γ-irradiated PBMCs revealed distinct morphological changes, indicative for apoptotic and necroptotic cell death. While inhibition of apoptosis had no effect on the pro-angiogenic activity of the secretome, inhibiting necroptosis in stressed PBMCs abolished blood vessel sprouting. Mechanistically, we identified tumor necrosis factor (TNF) receptor superfamily member 1B as the main driver of necroptosis in response to γ-irradiation in PBMCs, which was most likely mediated via membrane-bound TNF-α. In conclusion, our study demonstrates that the pro-angiogenic activity of the secretome of γ-irradiated PBMCs requires interplay of different PBMC subpopulations. Furthermore, we show that TNF-dependent necroptosis is an indispensable molecular process for conferring tissue-regenerative activity and for the pro-angiogenic potential of the PBMC secretome. These findings contribute to a better understanding of secretome-based therapies in regenerative medicine.

Film interface for drug testing for delivery to cells in culture and in the brain

Brain access remains a major challenge in drug testing. The nearly 'impermeable' blood-brain-barrier (BBB) prevents most drugs from gaining access to brain cells via systematic intravenous (IV) injection. In this study, silk fibroin films were used as drug carrier as well as cell culture substrate to simulate the in vivo interface between drug reservoir and brain cells for testing drug delivery in the brain. In in vitro studies, film-released arabinofuranosyl cytidine (AraC), a mitotic inhibitor, selectively killed glial cells in film-supported mixed neural cell cultures; with widened dosage windows for drug efficacy and tolerance compared to drugs in solution. In the brain, the presence of silk films was well tolerated with no signs of acute neuroinflammation, cell death, or altered brain function. Topical application of silk films on the cortical surface delivered Evans blue, a BBB-impenetrable fluorescent marker, through the intact dura matter into the parenchyma of the ipsilateral hemisphere as deep as the hippocampal region, but not the contralateral hemisphere. In a mouse traumatic brain injury (TBI) model, necrosis markers by film delivery accessed more cells in the lesion core than by con-current IV delivery; whereas the total coverage including the peri-lesional area appeared to be comparable between the two routes. The complementary distribution patterns of co-delivered markers provided direct evidence of the partial confinement of either route's access to brain cells by a restrictive zone near the lesion border. Finally, film-delivered necrostatin-1 reduced overall cell necrosis by approximately 40% in the TBI model. These findings from representative small molecules of delivery route-dependent drug access are broadly applicable for evaluating drug actions both in vitro and in vivo. Combined with its demonstrated role of supporting neuron-electrode interfaces, the film system can be further developed for testing a range of neuromodulation approaches (i.e., drug delivery, electrical stimulation, cell graft) in the brain. STATEMENT OF SIGNIFICANCE: This study demonstrated that silk fibroin films can be used to evaluate drug actions both in vitro and in vivo, partially overcoming the significant delivery barriers of the brain. This system can be adapted for efficient drug access to specific brain regions and/or cell types. The film system can be further developed for testing a range of interventions with drugs, electrical signals or cell graft for analysis of treatment outcomes including cell responses and brain function.

Necrostatin-1 Prevents Necroptosis in Brains after Ischemic Stroke via Inhibition of RIPK1-Mediated RIPK3/MLKL Signaling

Pharmacological studies have indirectly shown that necroptosis participates in ischemic neuronal death. However, its mechanism has yet to be elucidated in the ischemic brain. TNFα-triggered RIPK1 kinase activation could initiate RIPK3/MLKL-mediated necroptosis under inhibition of caspase-8. In the present study, we performed middle cerebral artery occlusion (MCAO) to induce cerebral ischemia in rats and used immunoblotting and immunostaining combined with pharmacological analysis to study the mechanism of necroptosis in ischemic brains. In the ipsilateral hemisphere, we found that ischemia induced the increase of (i) RIPK1 phosphorylation at the Ser166 residue (p-RIPK1), representing active RIPK1 kinase and (ii) the number of cells that were double stained with P-RIPK1 (Ser166) (p-RIPK1⁺) and TUNEL, a label of DNA double-strand breaks, indicating cell death. Furthermore, ischemia induced activation of downstream signaling factors of RIPK1, RIPK3 and MLKL, as well as the formation of mature interleukin-1β (IL-1β). Treatment with necrostatin-1 (Nec-1), an inhibitor of necroptosis, significantly decreased ischemia-induced increase of p-RIPK1 expression and p-RIPK1⁺ neurons, which showed protection from brain damage. Meanwhile, Nec-1 reduced RIPK3, MLKL and p-MLKL expression levels and mature IL-1β formation in Nec-1 treated ischemic brains. Our results clearly demonstrated that phosphorylation of RIPK1 at the Ser166 residue was involved in the pathogenesis of necroptosis in the brains after ischemic injury. Nec-1 treatment protected brains against ischemic necroptosis by reducing the activation of RIPK1 and inhibiting its downstream signaling pathways. These results provide direct in vivo evidence that phosphorylated RIPK1 (Ser 166) plays an important role in the initiation of RIPK3/MLKL-dependent necroptosis in the pathogenesis of ischemic stroke in the rodent brain.

RIPK1 inhibitor Cpd-71 attenuates renal dysfunction in cisplatin-treated mice via attenuating necroptosis, inflammation and oxidative stress

Acute kidney injury (AKI) is a destructive clinical condition induced by multiple insults including ischemic reperfusion, nephrotoxic drugs and sepsis. It is characterized by a sudden decline in renal function, in addition to excessive inflammation, oxidative stress and programmed cell death of renal tubular epithelial cells. RIPK1-mediated necroptosis plays an important role in AKI. In the present study, we evaluated the treatment effects of Compound-71 (Cpd-71), a novel RIPK1 inhibitor, by comparing with Necrostatin-1 (Nec-1), a classic RIPK1 inhibitor, which has several drawbacks like the narrow structure–activity relationship (SAR) profile, moderate potency and non-ideal pharmacokinetic properties, in vivo and in vitro. Our results showed that pretreatment of Cpd-71 attenuated cisplatin-induced renal injury, restored renal function and suppressed renal inflammation, oxidative stress and cell necroptosis. In addition, Cpd-71 inhibited renal damage while reducing the up-regulated serum creatinine (Cr) and blood urea nitrogen (BUN) levels in established AKI mice model. Consistently, we confirmed that Cpd-71 exhibited more effectively suppressive effect on cisplatin-induced renal tubular cell necroptosis than Nec-1, by physically binding to the allosteric type III ligand binding site of RIPK1, thereby reduced RIPK1 kinase activity, RIPK1/RIPK3 complex formation and phosphor-MLKL membrane translocation by molecular docking, Western blot, co-immunoprecipitation and cellular thermal shift assay (CETSA). Taken together, we currently showed that targeting RIPK1 with Cpd-71 may serve as a promising clinical candidate for AKI treatment.