Upregulation of the receptor-interacting protein 3 expression and involvement in neural tissue damage after spinal cord injury in mice

RIP1 inhibition protects retinal ganglion cells in glaucoma models of ocular injury

Receptor-interacting protein 1 (RIP1, RIPK1) is a critical mediator of multiple signaling pathways that promote inflammatory responses and cell death. The kinase activity of RIP1 contributes to the pathogenesis of a number of inflammatory and neurodegenerative diseases. However, the role of RIP1 in retinopathies remains unclear. This study demonstrates that RIP1 inhibition protects retinal ganglion cells (RGCs) in preclinical glaucoma models. Genetic inactivation of RIP1 improves RGC survival and preserves retinal function in the preclinical glaucoma models of optic nerve crush (ONC) and ischemia-reperfusion injury (IRI). In addition, the involvement of necroptosis in ONC and IRI glaucoma models was examined by utilizing RIP1 kinase-dead (RIP1-KD), RIP3 knockout (RIP3-KO), and MLKL knockout (MLKL-KO) mice. The number of RGCs, retinal thickness, and visual acuity were rescued in RIP1-kinase-dead (RIP1-KD) mice in both models, while wild-type (WT) mice experienced significant retinal thinning, RGC loss, and vision impairment. RIP3-KO and MLKL-KO mice showed moderate protective effects in the IRI model and limited in the ONC model. Furthermore, we confirmed that a glaucoma causative mutation in optineurin, OPTN-E50K, sensitizes cells to RIP1-mediated inflammatory cell death. RIP1 inhibition reduces RGC death and axonal degeneration following IRI in mice expressing OPTN-WT and OPTN-E50K variant mice. We demonstrate that RIP1 inactivation suppressed microglial infiltration in the RGC layer following glaucomatous damage. Finally, this study highlights that human glaucomatous retinas exhibit elevated levels of TNF and RIP3 mRNA and microglia infiltration, thus demonstrating the role of neuroinflammation in glaucoma pathogenesis. Altogether, these data indicate that RIP1 plays an important role in modulating neuroinflammation and that inhibiting RIP1 activity may provide a neuroprotective therapy for glaucoma.

Therapeutic effects of exendin-4 on spinal cord injury via restoring autophagy function and decreasing necroptosis in neuron

AIMS

Necroptosis is one of programmed death that may aggravate spinal cord injury (SCI). We aimed to investigate the effect and mechanism of exendin-4 (EX-4) on the recovery of motor function and necroptosis after SCI.

METHODS

The SD rats with left hemisection in the T10 spinal cord as SCI model were used. The behavior tests were measured within 4 weeks. The effects of EX-4 on necroptosis-associated proteins and autophagy flux were explored. In addition, the SHSY5Y cell model was introduced to explore the direct effect of EX-4 on neurons. The effect of lysosome was explored using mTOR activator and AO staining.

RESULTS

EX-4 could improve motor function and limb strength, promote the recovery of autophagy flux, and accelerate the degradation of necroptosis-related protein at 3 d after injury in rats. EX-4 reduced lysosome membrane permeability, promoted the recovery of lysosome function and autophagy flux, and accelerated the degradation of necroptosis-related proteins by inhibiting the phosphorylation level of mTOR in the SHSY5Y cell model.

CONCLUSION

Our results demonstrated that EX-4 may improve motor function after SCI via inhibiting mTOR phosphorylation level and accelerating the degradation of necroptosis-related proteins in neurons. Our findings may provide new therapeutic targets for clinical treatment after SCI.

Inhibition of autophagy and RIP1/RIP3/MLKL-mediated necroptosis by edaravone attenuates blood spinal cord barrier disruption following spinal cord injury

The disruption of the blood spinal cord barrier (BSCB) after spinal cord injury (SCI) can trigger secondary tissue damage. Edaravone is likely to protect the BSCB as a free radical scavenger, whereas it has been rarely reported thus far. In this study, the protective effect of edaravone was investigated with the use of compression spinal cord injured rats and human brain microvascular endothelial cells (HBMECs) injury. As indicated by the result of this study, edaravone treatment facilitated functional recovery after rats were subjected to SCI, ameliorated the vascular damage, and up-regulated the expression of BSCB-associated proteins. In vitro results, edaravone improved HBMECs viability, restored intercellular junctions, and promoted cellular angiogenic activities. It is noteworthy that autophagy was activated and RIP1/RIP3/MLKL phosphorylation was notably up-regulated. However, edaravone treatment exhibited the capability of mitigating above-mentioned tendency in vivo and in vitro. Moreover, rapamycin (Rapa) treatment deteriorated the protective effect of edaravone while aggravating the phosphorylation of RIP1/RIP3/MLKL expression. In the model of necrotic activator-induced HBMECs, autophagic expression was increased, whereas edaravone prevented autophagy and phosphorylation of RIP1/RIP3/MLKL. In general, our results suggested that edaravone is capable of reducing the destruction of BSCB and promoting functional recovery after SCI. The possible underlying mechanism is that edaravone is capable of protecting angiogenic activity and improving autophagy and the phosphorylation of RIP1/RIP3/MLKL, as well as their mutual deterioration. Accordingly, edaravone can be a favorable option for the treatment of SCI.

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.

Receptor-Interacting Protein Kinase 3 Inhibition Relieves Mechanical Allodynia and Suppresses NLRP3 Inflammasome and NF-κB in a Rat Model of Spinal Cord Injury

Background

Neuroinflammation is critical in developing and maintaining neuropathic pain after spinal cord injury (SCI). The receptor-interacting protein kinase 3 (RIPK3) has been shown to promote inflammatory response by exerting its non-necroptotic functions. In this study, we explored the involvement of RIPK3 in neuropathic pain after SCI.

Methods

Thoracic (T10) SCI rat model was conducted, and the mechanical threshold in rats was measured. The expressions of RIPK3, nod-like receptor family pyrin domain-containing protein 3 (NLRP3), caspase-1, and nuclear factor-κB (NF-κB) were measured with western blotting analysis or quantitative real-time polymerase chain reaction (qRT-PCR). Double immunofluorescence staining was used to explore the colabeled NLRP3 with NeuN, glial fibrillary acidic protein (GFAP), and ionized calcium-binding adapter molecule 1 (IBA1). In addition, enzyme-linked immunosorbent assay (ELISA) was applied to analyze the levels of proinflammatory factors interleukin 1 beta (IL-1β), interleukin 18 (IL-18), and tumor necrosis factor alpha (TNF-α).

Results

The expression of RIPK3 was elevated from postoperative days 7–21, which was consistent with the development of mechanical allodynia. Intrathecal administration of RIPK3 inhibitor GSK872 could alleviate the mechanical allodynia in SCI rats and reduce the expression levels of RIPK3. The activation of NLRP3 inflammasome and NF-κB was attenuated by GSK872 treatment. Furthermore, immunofluorescence suggested that NLRP3 had colocalization with glial cells and neurons in the L4–L6 spinal dorsal horns. In addition, GSK872 treatment reduced the production of inflammatory cytokines.

Conclusion

Our findings indicated that RIPK3 was an important facilitated factor for SCI-induced mechanical allodynia. RIPK3 inhibition might relieve mechanical allodynia by inhibiting NLRP3 inflammasome, NF-κB, and the associated inflammation.

Apoptosis and necroptosis occur in the different brain regions of hippocampus in a rat model of hypoxia asphyxia

AIM OF THE STUDY

Hypoxic-ischemic encephalopathy (HIE) is a major cause of newborn brain injury. Apoptosis and necroptosis are two forms of cell death which may occur in HIE but reported data are yet limited. This study investigates the expression of receptor interacting protein kinase (RIPK) 1 and 3, and caspase3, the key modulators of necroptosis and apoptosis, respectively, in a model of HIE to determine whether both forms of cell death occur in the corresponding brain regions.

MATERIALS AND METHODS

Postneonatal day 7 Sprague-Dawley rats were subjected to right carotid artery ligation followed by hypoxia or subjected to skin incision under surgical anesthesia without ligation and hypoxia. Neuroglioma (H4) cell was cultured and subjected to 24 h hypoxic insults. Necrostatin-1, a RIPK1 inhibitor, was administered in both in vivo and in vitro settings before insult.

RESULTS

After hypoxic-ischemic insults, both RIPK1 and RIPK3 expression were significantly increased in the region of hippocampal dentate gyrus in the injurious hemisphere. However, cleaved caspase3 was significantly increased in the hippocampal cornu ammonis 1 region in the injurious hemisphere. After hypoxic insults, RIPK1 and RIPK3 expression was also found in H4 cells. In addition, it was identified that the increased RIPK1 and RIPK3 can be inhibited by necrostatin-1 in both in vivo and in vitro.

CONCLUSIONS

These data indicated that apoptosis and necroptosis occur in different brain regions of hippocampus in a model of HIE which may suggest that strategies to prevent each form of neuronal death is valuable to be developed.

Regenerative replacement of neural cells for treatment of spinal cord injury

Introduction: Traumatic Spinal Cord Injury (SCI) results from primary physical injury to the spinal cord, which initiates a secondary cascade of neural cell death. Current therapeutic approaches can attenuate the consequences of the primary and secondary events, but do not address the degenerative aspects of SCI. Transplantation of neural stem/progenitor cells (NPCs) for the replacement of the lost/damaged neural cells is suggested here as a regenerative approach that is complementary to current therapeutics.Areas Covered: This review addresses how neurons, oligodendrocytes, and astrocytes are impacted by traumatic SCI, and how current research in regenerative-NPC therapeutics aims to restore their functionality. Methods used to enhance graft survival, as well as bias progenitor cells towards neuronal, oligodendrogenic, and astroglia lineages are discussed.Expert Opinion: Despite an NPC's ability to differentiate into neurons, oligodendrocytes, and astrocytes in the transplant environment, their potential therapeutic efficacy requires further optimization prior to translation into the clinic. Considering the temporospatial identity of NPCs could promote neural repair in region specific injuries throughout the spinal cord. Moreover, understanding which cells are targeted by NPC-derived myelinating cells can help restore physiologically-relevant myelin patterns. Finally, the duality of astrocytes is discussed, outlining their context-dependent importance in the treatment of SCI.

Transplantation of olfactory ensheathing cells promotes the therapeutic effect of neural stem cells on spinal cord injury by inhibiting necrioptosis

Transplantation of neural stem cells (NSCs) is one of the most promising treatments for spinal cord injury (SCI). However, the limited survival of transplanted NSCs reduces their therapeutic effects. The aim of the present study was to examine whether a co-transplantation of olfactory ensheathing cells (OECs) may enhance the survival of NSCs and improve the beneficial effects of NSCs in rats with SCI, as well as to investigate potential mechanisms underlying such efficacies. Co-transplantation of OECs and NSCs was used to treat rats with SCI. Sympathetic nerve function was determined by measuring sympathetic skin responses. The results showed that OEC/NSC co-transplantation improved motor function and autonomic nerve function in rats with SCI. Co-transplantation of OECs promoted NSC-induced neuroprotection and inhibited programmed necrosis of NSCs, which was mediated by receptor-interacting protein kinase 3 (RIP3) and mixed lineage kinase domain-like protein (MLKL). Furthermore, OECs increased the proliferation and differentiation of NSCs in vitro, and improved the survival rate of NSCs in vivo. Taken together, we conclude that transplantation of OECs inhibited programmed necrosis of co-transplanted NSCs to promote therapeutic effects on SCI. Therefore, co-transplantation of OECs and NSCs may represent a promising strategy for treating patients with SCI.

Novel Methods of Necroptosis Inhibition for Spinal Cord Injury Using Translational Research to Limit Secondary Injury and Enhance Endogenous Repair and Regeneration

Spinal cord injuries (SCIs) pose an immense challenge from a clinical perspective as current treatments and interventions have been found to provide marginal improvements in clinical outcome (with varying degrees of success) particularly in areas of motor and autonomic function. In this review, the pathogenesis of SCI will be described, particularly as it relates to the necroptotic pathway which has been implicated in limiting recovery of SCI via its roles in neuronal cell death, glial scarring, inflammation, and axonal demyelination and degeneration. Major mediators of the necroptotic pathway including receptor-interacting protein kinase 1, receptor-interacting protein kinase 3, and mixed-lineage kinase domain-like will be described in detail regarding their role in facilitating necroptosis. Additionally, due to the rapid accumulation of reactive oxygen species and inflammatory markers, the onset of necroptosis can begin within hours following SCI, thus developing therapeutics that readily cross the blood-brain barrier and inhibit necroptosis during these critical periods of inflammation are imperative in preventing irreversible damage. As such, current therapeutic interventions regarding SCI and targeting of the necroptotic pathway will be explored as will discussion of potential future therapeutics that show promise in minimizing long-term or permanent damage to the spinal cord following severe injury.

Genetic inactivation of RIP1 kinase does not ameliorate disease in a mouse model of ALS

RIP1 kinase is proposed to play a critical role in driving necroptosis and inflammation in neurodegenerative disorders, including Amyotrophic Lateral Sclerosis (ALS). Preclinical studies indicated that while pharmacological inhibition of RIP1 kinase can ameliorate axonal pathology and delay disease onset in the mutant SOD1 transgenic (SOD1-Tg) mice, genetic blockade of necroptosis does not provide benefit in this mouse model. To clarify the role of RIP1 kinase activity in driving pathology in SOD1-Tg mice, we crossed SOD1-Tgs to RIP1 kinase-dead knock-in mice, and measured disease progression using functional and histopathological endpoints. Genetic inactivation of the RIP1 kinase activity in the SOD1-Tgs did not benefit the declining muscle strength or nerve function, motor neuron degeneration or neuroinflammation. In addition, we did not find evidence of phosphorylated RIP1 accumulation in the spinal cords of ALS patients. On the other hand, genetic inactivation of RIP1 kinase activity ameliorated the depletion of the neurotransmitter dopamine in a toxin model of dopaminergic neurodegeneration. These findings indicate that RIP1 kinase activity is dispensable for disease pathogenesis in the SOD1-Tg mice while inhibition of kinase activity may provide benefit in acute injury models.

Experimental infection of hepatitis E virus induces pancreatic necroptosis in miniature pigs

Infection by hepatitis E virus (HEV) via the oral route causes acute hepatitis. Extra-hepatic manifestations of HEV infection may stem from various causes; however, its distribution in organs such as the liver, as well as the mechanisms underlying HEV-induced cell injury, remain unclear. The objective of this study was to determine the chronological distribution of HEV in various tissues of HEV-challenged miniature pigs and to investigate the mechanisms underlying HEV-induced cell death in the pancreas and liver. Virological and serological analyses were performed on blood and faecal samples. Histopathology of the liver and extra-hepatic tissues was analysed. Cell death pathways and immune cell characterisation in inflammatory lesions were analysed using immunohistochemistry. The liver and pancreas displayed inflammation and cellular injury, and a large amount of HEV was observed in the lesions. The liver was infiltrated by T and natural killer cells. HEV was identified in all organs except the heart, and was associated with immune cells. Although the liver and the pancreas strongly expressed TNF-α and TRAIL, TUNEL assay results were negative. RIP3 and pMLKL were expressed in the pancreas. RIP3, but not pMLKL, was expressed in the liver. Pancreatitis induced in HEV-infected miniature pigs is associated with necroptosis.

The Lipoxin A4 Receptor Agonist BML-111 Alleviates Inflammatory Injury and Oxidative Stress in Spinal Cord Injury

Background

Spinal cord injury (SCI) has a high incidence and causes serious harm. Lipoxin A4 (LXA4) receptor agonist BML-111 was reported to regulate inflammation and oxidative stress. The goal of this study was to assess whether BML-111 could protect against SCI by suppressing inflammation and oxidative stress.

Material/Methods

We developed a rat SCI model, then BML-111 was intraperitoneally injected into SCI rats to observe the BML-111 function. The pathological changes of SCI were observed with hematoxylin and eosin (HE) staining. Motor function of rats were assessed by the modified Tarlov’s scale. ELISA was used to assess the changes in levels of TNF-α, IL-1β, and IL-6. Western blot analysis was performed to assess the expressions of TNF-α, IL-1β, IL-6, Bcl2, Bax, and cleaved caspase3 in spinal cord tissue. TOS and TAS in rat serum were detected by xylenol orange method and ABTS method, respectively. The apoptotic cells in spinal cord tissue were observed with TUNEL assay.

Results

The results indicated that BML-111 effectively improved the SCI and motor function of rats. BML-111 treatment decreased the levels of TNF-α, IL-1β, and IL-6 in serum and spinal cord tissue, as well as decreasing the levels of TOS and TAS and cell apoptosis.

Conclusions

BML-111 alleviated inflammation and oxidative stress in SCI rats.

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.

Deletion of Ripk3 Prevents Motor Neuron Death In Vitro but not In Vivo

Increasing evidence suggests that necroptosis, a form of programmed cell death (PCD), contributes to neurodegeneration in several disorders, including ALS. Supporting this view, investigations in both in vitro and in vivo models of ALS have implicated key molecular determinants of necroptosis in the death of spinal motor neurons (MNs). Consistent with a pathogenic role of necroptosis in ALS, we showed increased mRNA levels for the three main necroptosis effectors Ripk1, Ripk3, and Mlkl in the spinal cord of mutant superoxide dismutase-1 (SOD1G93A) transgenic mice (Tg), an established model of ALS. In addition, protein levels of receptor-interacting protein kinase 1 (RIPK1; but not of RIPK3, MLKL or activated MLKL) were elevated in spinal cord extracts from these Tg SOD1G93A mice. In postmortem motor cortex samples from sporadic and familial ALS patients, no change in protein levels of RIPK1 were detected. Silencing of Ripk3 in cultured MNs protected them from toxicity associated with SOD1G93A astrocytes. However, constitutive deletion of Ripk3 in Tg SOD1G93A mice failed to provide behavioral or neuropathological improvement, demonstrating no similar benefit of Ripk3 silencing in vivo. Lastly, we detected no genotype-specific myelin decompaction, proposed to be a proxy of necroptosis in ALS, in either Tg SOD1G93A or Optineurin knock-out mice, another ALS mouse model. These findings argue against a role for RIPK3 in Tg SOD1G93A-induced neurodegeneration and call for further preclinical investigations to determine if necroptosis plays a critical role in the pathogenesis of ALS.

MLKL-PITPα signaling-mediated necroptosis contributes to cisplatin-triggered cell death in lung cancer A549 cells

Necroptosis has been reported to be involved in cisplatin-induced cell death, but the mechanisms underlying the occurrence of necroptosis are not fully elucidated. In this study, we show that apart from apoptosis, cisplatin induces necroptosis in A549 cells. The alleviation of cell death by two necroptosis inhibitors-necrostatin-1 (Nec-1) and necrosulfonamide (NSA), and the phosphorylation of mixed lineage kinase domain-like protein (MLKL) at serine 358, suggest the involvement of receptor-interacting protein kinase 1 (RIPK1)-RIPK3-MLKL signaling in cisplatin-treated A549 cells. Additionally, the initiation of cisplatin-induced necroptosis relies on autocrine tumor necrosis factor alpha (TNF-α). Furthermore, we present the first evidence that phosphatidylinositol transfer protein alpha (PITPα) is involved in MLKL-mediated necroptosis by interacting with the N terminal MLKL on its sixth helix and the preceding loop, which facilitates MLKL oligomerization and plasma membrane translocation in necroptosis. Silencing of PITPα expression interferes with MLKL function and reduces cell death. Our data elucidate that cisplatin-treated lung cancer cells undergo a new type of programmed cell death called necroptosis and shed new light on how MLKL translocates to the plasma membrane.

Inhibiting RIPK1 Limits Neuroinflammation and Alleviates Postoperative Cognitive Impairments in D-Galactose-Induced Aged Mice

Neuroinflammation plays a critical role in the pathogenesis of postoperative cognitive dysfunction (POCD) of the elderly patients. Receptor-interacting protein kinase1 (RIPK1) is a key molecular switch modulating inflammation, apoptosis and necroptosis. Here, we investigated whether inhibiting RIPK1 by necrostatin-1 (Nec-1) could limit neuroinflammation and attenuate POCD in D-Galactose (D-Gal)-induced aged mice. The mice were subjected to anesthesia and partial hepatectomy, and necrostatin-1 was administered intraperitoneally 1 h prior to anesthesia and surgery. Cognitive function and movement were tested 24 h after surgery by open field, Barnes maze and puzzle box. The hippocampal tissues were collected to detect the following: neuroinflammation (Iba-1, IL-1α, IL-1β, TNF-α), Necroptosis (Propidium Iodide (PI) labeling, RIPK1, nuclear transcription factor kappa B (NF-κB) and neuroplasticity (doublecortin (DCX), NR2B, GluA1, GluA2). We found that anesthesia and surgery induced a significant deficit in spatial memory acquisition and impairment of executive function and memory to simple task in D-Galactose-induced aged mice. Inhibiting RIPK1 by necrostatin-1 strikingly mitigated cognitive impairment and alleviated postoperative amplified neuroinflammation, necroptosis and GluA1 loss in hippocampus. These suggest that targeting RIPK1 by necrostatin-1 may serve as a promising therapeutics for prevention of POCD in elderly patients.

Neuronal Cell Death

Neuronal cell death occurs extensively during development and pathology, where it is especially important because of the limited capacity of adult neurons to proliferate or be replaced. The concept of cell death used to be simple as there were just two or three types, so we just had to work out which type was involved in our particular pathology and then block it. However, we now know that there are at least a dozen ways for neurons to die, that blocking a particular mechanism of cell death may not prevent the cell from dying, and that non-neuronal cells also contribute to neuronal death. We review here the mechanisms of neuronal death by intrinsic and extrinsic apoptosis, oncosis, necroptosis, parthanatos, ferroptosis, sarmoptosis, autophagic cell death, autosis, autolysis, paraptosis, pyroptosis, phagoptosis, and mitochondrial permeability transition. We next explore the mechanisms of neuronal death during development, and those induced by axotomy, aberrant cell-cycle reentry, glutamate (excitoxicity and oxytosis), loss of connected neurons, aggregated proteins and the unfolded protein response, oxidants, inflammation, and microglia. We then reassess which forms of cell death occur in stroke and Alzheimer's disease, two of the most important pathologies involving neuronal cell death. We also discuss why it has been so difficult to pinpoint the type of neuronal death involved, if and why the mechanism of neuronal death matters, the molecular overlap and interplay between death subroutines, and the therapeutic implications of these multiple overlapping forms of neuronal death.

Necrostatin-1 Mitigates Endoplasmic Reticulum Stress After Spinal Cord Injury

Necrostatin-1 (Nec-1) has been shown to inhibit necroptosis and convey a significant protective effect after spinal cord injury (SCI). This small molecule inhibitor may reduce tissue damage and restore neurological function by lessening mitochondrial injury after SCI and preserving energy homeostasis. However, the effects of Nec-1 on endoplasmic reticulum stress (ERS)-an important pathological consequence of SCI-are still not clear. The present study investigates the relationship between necroptosis and ERS in a rat model of SCI. Electron microscopy was employed to observe ultra-structural changes in the endoplasmic reticulum and mitochondria after lesioning. Real-time quantitative PCR was used to measure the mRNA levels of ERS-related pro-apoptotic molecules such as C/EBP homologous protein (CHOP), immunoglobulin-binding protein (BiP/GRP78) and X box-binding protein-1 (XBP-1). Western blot and immunofluorescence were conducted to analyze CHOP, GRP78 and XBP-1 protein expression after lesioning. Results demonstrated that applying Nec-1 in SCI reduces ultra-structural damage to the endoplasmic reticulum and mitochondria and inhibits expression of ERS-related genes and proteins after lesioning. Immunofluorescence also shows ERS-related proteins mainly expressed in the cytoplasm of nerve cells. Taken together, these results demonstrate that Nec-1 has protective effect on the endoplasmic reticulum and mitochondria and alleviates ERS after SCI.

The effects and regulatory mechanism of RIP3 on RGC-5 necroptosis following elevated hydrostatic pressure

Necroptosis is a type of regulated cell death that has been implicated in various diseases. Receptor-interacting protein 3 (RIP3), a member of the RIP family, is an important mediator of the necroptotic pathway. Cleavage of RIP3 at Asp328 by caspase-8 abolishes the kinase activity of RIP3, which is critical for necroptosis. Moreover, RIP3 is significantly upregulated during the early stages of acute high intra-ocular pressure and oxygen glucose deprivation. In this study, the effects of RIP3 during elevated hydrostatic pressure (EHP) were investigated and the possible mechanism through which caspase-8 regulated RIP3 cleavage was explored. Flow cytometry analysis revealed that the number of EHP-induced necrotic retinal ganglion cell 5 (RGC-5) cells was reduced after RIP3-knockdown. Furthermore, malondialdehyde (MDA) levels and glycogen phosphorylase (PYGL) activity in normal RGC-5 cells were much higher than those in RIP3-knockdown cells after EHP. EHP-induced RGC-5 necrosis was significantly reduced after treatment with butylated hydroxyanisole (BHA), a reactive oxygen species (ROS) scavenger. MDA levels and PYGL activity were lower in normal RGC-5 cells than those in cells with caspase-8 inhibition after EHP. Western blot analysis demonstrated that the RIP3 cleavage product was upregulated in cells with caspase-8 inhibition. Additionally, flow cytometry analysis revealed that the number of EHP-induced necrotic RGC-5 cells was increased after caspase-8 inhibition. Our results suggested that RGC-5 necroptosis following EHP was mediated by RIP3 through induction of PYGL activity and subsequent ROS accumulation. Thus, caspase-8 may participate in the regulation of RGC-5 necroptosis via RIP3 cleavage.

Necrostatin-1 attenuates early brain injury after subarachnoid hemorrhage in rats by inhibiting necroptosis

Necroptosis is programmed cell death that has been recently proposed and reported to be involved in several neurologic diseases. However, the role of necroptosis in early brain injury after subarachnoid hemorrhage (SAH) is still unknown. The purpose of this study was to investigate whether necroptosis was involved in SAH-induced early brain injury, and to assess the possible neuroprotective effect of necrostatin-1 using an endovascular perforation rat model of SAH. Our results showed that the expression levels of necroptosis-related proteins including RIP1, RIP3 and MLKL in the basal cortex all increased at 3 hours after SAH (P<0.05) and peaked at 48 hours after SAH (P<0.05). However, they were greatly reduced after treatment with necrostatin-1 (P<0.05). Concurrently, neurologic outcomes were significantly improved after necrostatin-1 treatment (P<0.05). Furthermore, brain edema, blood-brain barrier disruption, necrotic cell death and neuroinflammation were also greatly inhibited after necrostatin-1 treatment. These results indicate that necroptosis is an important mechanism of cell death involved in the early brain injury after experimental SAH. Necrostatin-1 perhaps can serve as a promising neuroprotective agent for SAH treatment.

Upregulation of PSMB4 is Associated with the Necroptosis after Spinal Cord Injury

Spinal cord injury (SCI) is one of the most common and severe complications in spine injury. It is difficult to prevent cell necroptosis and promote the survival of residual neurons after SCI. Proteasome beta-4 subunit (PSMB4) is the first proteasomal subunit with oncogenic properties promoting cancer cell survival and tumor growth in vivo, and our previous study showed that PSMB4 is significantly associated with neuronal apoptosis in neuroinflammation. However, PSMB4 function in the necroptosis after SCI is unkown. RIP3, a key regulatory factor of necroptosis, correlates with the induction of necroptosis in various types of cells and signaling pathway. Upregulation of the RIP3 expression may play a role as a novel molecular mechanism in secondary neural tissue damage following SCI. In this study, we established an acute spinal cord contusion injury model in adult rats to investigate the potential role of PSMB4 during the pathological process of SCI. We found PSMB4 expression was significantly up-regulated 3 days after injury by western blot and immunohistochemical staining. Double immunofluorescent staining indicated obvious changes of PSMB4 expression occurred in neurons. Significant up-regulation of PSMB4 expression was observed in Rip3 positive neurons at 3 days after SCI, which indicated that PSMB4 might play a vital role in the regulation of Rip3. Overexpress and knockdown PSMB4 could intervene the RIP3 and Mixed lineage kinase domain-like protein (MLKL) pathway in Tumor necrosis factor-α (TNF-α) induced necroptosis cell model. Based on our experimental data, we boldly conclude that PSMB4 is associated with RIP3 involved necroptosis after SCI.

Expression Profile and Tissue-Specific Distribution of the Receptor-Interacting Protein 3 in BALB/c Mice

RIP3, a member of receptor-interacting protein family, is serine/threonine kinase that contributes to necrosis and promotes systematic inflammation. However, detailed information of the expression pattern and tissue distribution in BALB/c mice, a commonly used laboratory animal model, is still unavailable. Here, we provided the basic data of expression profile and histologic distribution of RIP3 in tissues of BALB/c mice. Rip3 mRNA expression levels and tissue distribution were detected by real-time quantitative PCR and immunohistochemical detection, respectively. Rip3 mRNA expression showed the highest level in the spleen and duodenum, while with the lowest level in brain. Immunohistochemical detection revealed this protein located in different type cells in different tissues. What's more, the obvious positive staining in nuclear was detected in liver cells and neurons in cerebral cortex of the brain, while cells in other organs, including heart, spleen, lung, kidney, stomach, duodenum and trachea, showed strong positive mainly in cytoplasm. The results will help us to further understand the site-specific functions of RIP3 in necrosis and inflammatory responses.