Inhibition of c-Jun N-terminal kinase ameliorates early brain injury after subarachnoid hemorrhage through inhibition of a Nur77 dependent apoptosis pathway

Emodin Protects Against Lipopolysaccharide-Induced Acute Lung Injury via the JNK/Nur77/c-Jun Signaling Pathway

Background: Acute lung injury (ALI) is a serious inflammatory disease with clinical manifestations of hypoxemia and respiratory failure. Presently, there is no effective treatment of ALI. Although emodin from Rheum palmatum L. exerts anti-ALI properties, the underlying mechanisms have not been fully explored.

Purpose: This study aimed to investigate the therapeutic effect and mechanism of emodin on LPS-induced ALI in mice.

Methods: RAW264.7 cells and zebrafish larvae were stimulated by LPS to establish inflammatory models. The anti-inflammatory effect of emodin was assessed by ELISA, flow cytometric analysis, and survival analysis. In vitro mechanisms were explored by using Western blotting, luciferase assay, electrophoretic mobility shift assay (EMSA), and small interfering RNA (siRNA) approach. The acute lung injury model in mice was established by the intratracheal administration of LPS, and the underlying mechanisms were assessed by detecting changes in histopathological and inflammatory markers and Western blotting in lung tissues.

Results: Emodin inhibited the inflammatory factor production and oxidative stress in RAW264.7 cells, and prolonged the survival of zebrafish larvae after LPS stimulation. Emodin suppressed the expression levels of phosphorylated JNK at Thr183/tyr182 and phosphorylated Nur77 at Ser351 and c-Jun, and increased the expression level of Nur77 in LPS-stimulated RAW264.7 cells, while these regulatory effects of emodin on Nur77/c-Jun were counteracted by JNK activators. The overexpression of JNK dampened the emodin-mediated increase in Nur77 luciferase activity and Nur77 expression. Moreover, the inhibitory effect of emodin on c-Jun can be attenuated by Nur77 siRNA. Furthermore, emodin alleviated LPS-induced ALI in mice through the regulation of the JNK/Nur77/c-Jun pathway.

Conclusions: Emodin protects against LPS-induced ALI through regulation on JNK/Nur77/c-Jun signaling. Our results indicate the potential of emodin in the treatment of ALI.

Progress and Promise of Nur77-based Therapeutics for Central Nervous System Disorders

Nur77 belongs to the NR4A subgroup of the nuclear receptor superfamily. Unlike other nuclear receptors, a natural ligand for Nur77 has not been identified yet. However, a few small molecules can interact with this receptor and induce a conformational change to mediate its activity. The expression and activation of Nur77 can be rapidly increased using various physiological and pathological stimuli. In vivo and in vitro studies have demonstrated its regulatory role in tissues and cells of multiple systems by means of participation in cell differentiation, apoptosis, metabolism, mitochondrial homeostasis, and other processes. Although research on Nur77 in the pathophysiology of the central nervous system (CNS) is currently limited, the present data support the fact that Nur77 is involved in many neurological disorders such as stroke, multiple sclerosis, Parkinson’s disease. This indicates that activation of Nur77 has considerable potential in treating these diseases. This review summarizes the regulatory mechanisms of Nur77 in CNS diseases and presents available evidence for its potential as targeted therapy, especially for cerebrovascular and inflammation-related CNS diseases.

NR4A1 regulates cerebral ischemia-induced brain injury by regulating neuroinflammation through interaction with NF-κB/p65

Stroke is reported as a leading cause of mortality and disability in the world. Neuroinflammation is significantly induced responding to ischemic stroke, and this process is accompanied with microglial activation. However, the pathogenesis contributing to ischemic stroke remains unclear. NR4A1 (Nur77) is a nuclear receptor that is expressed in macrophages, playing a significant role in regulating inflammatory response. In the present study, we attempted to explore the effects of NR4A1 on ischemic stroke using in vivo and in vitro studies. Results suggested that NR4A1 expression in microglia was markedly increased after cerebral ischemic damage. Then, we found that NR4A1 knockout attenuated ischemia-triggered infarction volume and neuron injury. Also, cognitive impairments were improved in ischemic mice with NR4A1 deficiency, resulting in functional improvements. Moreover, M1 polarization in microglia and neutrophil recruitment was significantly alleviated by NR4A1 deletion, as evidenced by the reduced expression of M1 markers, chemokines, as well as intracellular adhesion molecule-1 (ICAM-1) and myeloperoxidase (MPO) levels. Importantly, we found that NR4A1 could interact with nuclear factor-κB (NF-κB)/p65 based on in vivo and in vitro results. Suppressing p65 activation by the use of its inhibitor clearly reduced the NR4A1 expression, M1 polarization and neutrophil recruitments, while rescued the expression of anti-inflammatory factors in microglia treated with oxygen-glucose deprivation (OGD). Therefore, NR4A1 suppression in microglia restrained neuroinflammation through interacting with NF-κB/p65 to attenuate ischemic stroke.

c‑Jun N‑terminal kinase inhibition attenuates early brain injury induced neuronal apoptosis via decreasing p53 phosphorylation and mitochondrial apoptotic pathway activation in subarachnoid hemorrhage rats

Early brain injury (EBI)‑induced neuronal apoptosis is primarily responsible for the subsequent complications of aneurysmal subarachnoid hemorrhage (aSAH), which may increase the risk of mortality in patients with aSAH. c‑Jun N‑terminal kinase (JNK) has been demonstrated to be a promoter of EBI‑induced cell apoptosis, although the mechanism has yet to be fully elucidated. The present study aimed to explore whether the role of JNK1 is associated with tumor protein p53 (p53), which is one of the most important factor that triggers cell apoptosis. JNK1 expression was downregulated via in vivo small interfering RNA transfection in an aSAH rat model in order to assess differences in the behavior, survival times, morphology and genetics of the experimental animals. The results revealed that JNK1 inhibition improved the neurological scores and survival times of SAH rats by interrupting cascaded neuronal apoptosis. The interruption of EBI‑induced neuronal apoptosis may originate from a decrease in the level of p53 phosphorylation and deactivation of the downstream mitochondrial apoptotic pathway. Taken together, these results suggest that JNK1 may be a promising target for improving the prognosis of patients with aSAH.

Inhibition of myeloid differentiation primary response protein 88 provides neuroprotection in early brain injury following experimental subarachnoid hemorrhage

Accumulating of evidence suggests that activation of nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinases (MAPKs) exacerbates early brain injury (EBI) following subarachnoid hemorrhage (SAH) by provoking pro-inflammatory and pro-apoptotic signaling. Myeloid differentiation primary response protein 88 (MyD88) is an endogenous adaptor protein in the toll-like receptors (TLRs) and interleukin (IL) -1β family signaling pathways and acts as a bottle neck in the NF-κB and MAPK pathways. Here, we used ST2825, a selective inhibitor of MyD88, to clarify whether inhibiting MyD88 could provide neuroprotection in EBI following SAH. Our results showed that the expression of MyD88 was markedly increased at 24 h post SAH. Intracerebroventricular injection of ST2825 significantly reduced the expression of MyD88 at 24 h post SAH. Involvement of MAPKs and NF-κB signaling pathways was revealed that ST2825 inhibited SAH-induced phosphorylation of TAK1, p38 and JNK, the nuclear translocation of NF-κB p65, and degradation of IκBα. Further, ST2825 administration diminished the SAH-induced inflammatory response and apoptosis. As a result, SAH-induced EBI was alleviated and neurological deficits caused by SAH were reversed. Our findings suggest that MyD88 inhibition confers marked neuroprotection against EBI following SAH. Therefore, MyD88 might be a promising new molecular target for the treatment of SAH.

Ethyl Pyruvate Attenuates Early Brain Injury Following Subarachnoid Hemorrhage in the Endovascular Perforation Rabbit Model Possibly Via Anti-inflammation and Inhibition of JNK Signaling Pathway

Early brain injury (EBI) following subarachnoid hemorrhage (SAH) is the main cause to poor outcomes of SAH patients, and early inflammation plays an important role in the acute pathophysiological events. It has been demonstrated that ethyl pyruvate (EP) has anti-inflammatory and neuroprotective effects in various critical diseases, however, the role of EP on EBI following SAH remains to be elucidated. Our study aimed to evaluate the effects of EP on EBI following SAH in the endovascular perforation rabbit model. All rabbits were randomly divided into three groups: sham, SAH + Vehicle (equal volume) and SAH + EP (30 mg/kg/day). MRI was performed to estimate the reliability of the EBI at 24 and 72 h after SAH. Neurological scores were recorded to evaluate the neurological deficit, ELISA kit was used to measure the level of tumor necrosis factor-α (TNF-α), and western blot was used to detect the expression of TNF-α, tJNK, pJNK, bax and bcl-2 at 24 and 72 h after SAH. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and Fluoro-jade B (FJB) staining were used to detect neuronal apoptosis and neurodegeneration respectively, meanwhile hematoxylin and eosin (H&E) staining was used to assess the degree of vasospasm. Our results demonstrated that EP alleviated brain tissue injury (characterized by diffusion weighted imaging and T2 sequence in MRI scan), and significantly improved neurological scores at 72 h after SAH. EP decreased the level of TNF-α and downregulated pJNK/tJNK and bax/bcl-2 in cerebral cortex and hippocampus effectively both at 24 and 72 h after SAH. Furthermore, EP reduced TUNEL and FJB positive cells significantly. In conclusion, the present study supported that EP afforded neuroprotective effects possibly via reducing TNF-α expression and inhibition of the JNK signaling pathway. Therefore, EP may be a potent therapeutic agent to attenuate EBI following SAH.

Sex and Age Differences in Epinephrine Mechanisms and Outcomes after Brain Injury

Traumatic brain injury (TBI) is the leading cause of injury-related death in children, with boys and children <4 years of age having particularly poor outcomes. Cerebral autoregulation is often impaired after TBI, contributing to poor outcome. Cerebral perfusion pressure can be normalized by use of vasoactive agents. The c-Jun-terminal kinase (JNK) isoform of mitogen activated protein kinase (MAPK) produces hemodynamic impairment after TBI, but less is known about its role in histopathology. We investigated whether epinephrine (EPI), age, and sex dependently protected cerebral autoregulation and limited histopathology after TBI, and sought to determine the role of JNK in that outcome. Lateral fluid percussion injury (FPI) was produced in anesthetized pigs. Pial artery reactivity was measured via a closed cranial window. Phosphorylated JNK MAPK was quantified by enzyme-linked immunosorbent assay (ELISA). Results show that EPI preserves autoregulation, prevents histopathology, and blocks phosphorylated JNK upregulation in newborn males and females and juvenile females but not juvenile males after TBI. These data indicate that EPI preserves cerebral autoregulation and limits histopathology after TBI through blockade of JNK in an age- and sex-dependent manner.

Etanercept alleviates early brain injury following experimental subarachnoid hemorrhage and the possible role of tumor necrosis factor-α and c-Jun N-terminal kinase pathway

Cerebral inflammation plays a crucial role in early brain injury (EBI) after subarachnoid hemorrhage (SAH). This study investigated the effects of c-Jun N-terminal kinase (JNK) inhibitor SP600125, acetylcholine (Ach), etanercept, and anti-TNF-α on cellular apoptosis in the cerebral cortex and the hippocampus, in order to establish the role of JNK and TNF-α in EBI. The SAH model was established using an endovascular puncture protocol. The reliability of the EBI model was determined by phosphorylated-Bad (pBad) immunohistochemistry. Neurological scores were recorded and western blot was used to detect the expression of JNK and TNF-α, and TUNEL assay was used to mark apoptotic cells. The results showed that pBad positive cells were evenly distributed in the cerebral cortex at different time points. The highest expression of pBad was reached 1 day after SAH, and pJNK and TNF-α reached their peak expression at 2 days after SAH. SP600125, Ach, and etanercept significantly decreased the level of pJNK and TNF-α in the cerebral cortex and the hippocampus. In addition, SP600125 and etanercept reduced cellular apoptosis in the cerebral cortex and the hippocampus and significantly improved neurological scores at 2 days after SAH potentially via inhibition of the JNK-TNF-α pathway. Ach reduced cellular apoptosis only in the cerebral cortex. It is possible that JNK induces TNF-α expression, which in turn enhances JNK expression in EBI after SAH, leading to increased apoptosis in the cerebral cortex and the hippocampus. Thus, our results indicate that that etanercept may be a potential therapeutic agent to alleviate EBI.