Nuclear Heme Oxidase-1 Inhibits Endoplasmic Reticulum Stress-Mediated Apoptosis after Spinal Cord Injury

Crosstalk Between Cell Death and Spinal Cord Injury: Neurology and Therapy

Spinal cord injury (SCI) often leads to neurological dysfunction, and neuronal cell death is one of the main causes of neurological dysfunction. After SCI, in addition to necrosis, programmed cell death (PCD) occurs in nerve cells. At first, studies recognized only necrosis, apoptosis, and autophagy. In recent years, researchers have identified new forms of PCD, including pyroptosis, necroptosis, ferroptosis, and cuproptosis. Related studies have confirmed that all of these cell death modes are involved in various phases of SCI and affect the direction of the disease through different mechanisms and pathways. Furthermore, regulating neuronal cell death after SCI through various means has been proven to be beneficial for the recovery of neural function. In recent years, emerging therapies for SCI have also provided new potential methods to restore neural function. Thus, the relationship between SCI and cell death plays an important role in the occurrence and development of SCI. This review summarizes and generalizes the relevant research results on neuronal necrosis, apoptosis, autophagy, pyroptosis, necroptosis, ferroptosis, and cuproptosis after SCI to provide a new understanding of neuronal cell death after SCI and to aid in the treatment of SCI.

PKR inhibitor protects spinal cord injury through mitigating endoplasmic reticulum stress and pyroptosis

OBJECTIVES

The goal of the study was to reveal the regulatory role of protein kinase R (PKR) in spinal cord injury (SCI), a devasting disorder of the neurological system, and to elucidate its potential mechanism.

METHODS

The established animal and cellular models of SCI were treated by the PKR inhibitor C12. Histological injury and tissue apoptosis were assessed via H&E staining and TUNEL assays, respectively. Basso-Beattie-Bresnahan (BBB) scoring as well as forelimb grip strength tests were employed to evaluate functional recovery. The production of ROS and cytokines were appraised via their related commercial kits. Western blot and immunofluorescence assay were used to examine protein expression. CCK-8 method was used to assay cell activity. Co-immunoprecipitation assay was conducted to measure the affinity of PKR with STAT1.

RESULTS

PKR expression was enhanced following SCI, and the PKR inhibitor C16 mitigated histological injury, cell apoptosis and water content in spinal cord, and improved function recovery following SCI. Meanwhile, C16 attenuated ER stress, pyroptosis, NLRP3 inflammasome and inflammation in mice with SCI and in BV-2 cells challenged with LPS. Additionally, PKR interacted with STAT1 in BV-2 cells, and STAT1 knockdown inhibited ER stress, pyroptosis and inflammation in BV-2 cells challenged with LPS. The protective role of C16 in BV-2 cells exposed to LPS were partly abolished by STAT1 overexpression.

CONCLUSION

PKR inhibition might be a prospective effective approach to attenuating SCI and accelerating function recovery through modulating microglial pyroptosis and ER stress.

USP7 regulates HMOX-1 via deubiquitination to suppress ferroptosis and ameliorate spinal cord injury in rats

Heme oxygenase 1 (HMOX-1) is overexpressed in spinal cord injury (SCI) and relevant to ferroptosis. Ubiquitin-specific-processing protease 7 (USP7) has unveiled its role in regulating HMOX-1 stabilization while its function in SCI remains unknown. This study is to explore the potential molecular mechanism of the USP7-HMOX-1 axis in ferroptosis in a SCI rat model. SCI was assessed with Basso, Beattie, Bresnahan locomotion evaluation, hematoxylin-eosin histological staining, and immunofluorescence detection of NeuN. Ferroptosis was assessed by detections of the iron content, malondialdehyde and glutathione levels, mitochondrial damage, and glutathione peroxidase 4, 4-hydroxynonenal, USP7, and HMOX-1 expression in spinal cord. Co-immunoprecipitation was used to detect the binding of USP7 to HMOX-1. The ubiquitination level of HMOX-1 was measured after USP7 overexpression. USP7 expression was downregulated and HMOX-1 expression was upregulated in SCI rat models. HMOX-1 or USP7 overexpression promoted motor function recovery, ameliorated spinal cord damage, increased NeuN expression, and blocked the occurrence of ferroptosis in SCI rat models. In SCI rats, USP7 directly bound to HMOX-1 and its overexpression promoted HMOX-1 expression via deubiquitination. To sum up, USP7 overexpression facilitated the expression of HMOX-1 through deubiquitination, thereby reducing ferroptosis and alleviating SCI.

Ferroptosis related genes participate in the pathogenesis of spinal cord injury via HIF-1 signaling pathway

BACKGROUND

Spinal cord injury (SCI) is a crushing disease without a effective and specific therapeutic strategy. Therefore, it is crucial to uncover underlying mechanism in order to identify potential treatments for SCI. Current studies show ferroptosis might pay important role in SCI.

METHODS

In this study, we aimed to identify the key ferroptosis-related genes providing therapeutic targets for SCI. GSE45006, GSE19890 and GSE156999 from Gene Expression Omnibus (GEO) database were analyzed.

RESULTS

A total of 61 ferroptosis-related DEGs were identified, followed by bioinformatics enrichment analyses and PPI network construction. Ten key ferroptosis-related genes were identified by Cytoscape (Cytohubba), most of which were enriched in the HIF-1 signaling pathway. Then we constructed a clip SCI rat model and qPCR was performed to assess the expressions of five genes enriched in HIF-1 signaling pathway (Stat3, Tlr4, Hmox1, Hif1a and Cybb). Finally, a ceRNA network, Stat3, Tlr4, Hmox1/miR127, miR383, miR485/rno-Mut_0003, rno-Pwwp2a_0002 was constructed and expression of mentioned molecules were validated by chip data.

CONCLUSIONS

Five hub genes from HIF-1 signaling pathway were identified and might play a central role in SCI, which indicated that ferroptosis was correlated with HIF-1 signaling pathway. These results can provide a new insight into molecular mechanisms and identify potential therapeutic targets for SCI.

Protein disulfide isomerase A6 promotes the repair of injured nerve through interactions with spastin

The maintenance of appropriate endoplasmic reticulum (ER) homeostasis is critical to effective spinal cord injury (SCI) repair. In previous reports, protein disulfide isomerase A6 (PDIA6) demonstrated to serve as a reversible functional modulator of ER stress responses, while spastin can coordinate ER organization through the modulation of the dynamic microtubule network surrounding this organelle. While both PDIA6 and spastin are thus important regulators of the ER, whether they interact with one another for SCI repair still needs to be determined. Here a proteomics analysis identified PDIA6 as being related to SCI repair, and protein interaction mass spectrometry further confirmed the ability of PDIA6 and spastin to interact with one another. Pull-down and co-immunoprecipitation assays were further performed to validate and characterize the interactions between these two proteins. The RNAi-based knockdown of PDIA6 in COS-7 cells inhibited the activity of spastin-dependent microtubule severing. PDIA6 was also found to promote injured neuron repair, while spastin knockdown reversed this reparative activity. Together, these results thus confirm that PDIA6 and spastin function together as critical mediators of nerve repair, highlighting their potential value as validated targets for efforts to promote SCI repair.

The Nuclear Translocation of Heme Oxygenase-1 in Human Diseases

Heme oxygenase-1 (HO-1) is a rate-limiting enzyme in the degradation of heme to generate carbon monoxide (CO), free iron and biliverdin, which could then be converted to bilirubin by biliverdin reductase. HO-1 exhibits cytoprotective effects of anti-apoptosis, anti-oxidation, and anti-inflammation via these byproducts generated during the above process. In the last few years, despite the canonical function of HO-1 and possible biological significance of its byproducts, a noncanonical function, through which HO-1 exhibits functions in diseases independent of its enzyme activity, also has been reported. In this review, the noncanonical functions of HO-1 and its translocation in other subcellular compartments are summarized. More importantly, we emphasize the critical role of HO-1 nuclear translocation in human diseases. Intriguingly, this translocation was linked to tumorigenesis and tumor progression in lung, prostate, head, and neck squamous cell carcinomas and chronic myeloid leukemia. Given the importance of HO-1 nuclear translocation in human diseases, nuclear HO-1 as a novel target might be attractive for the prevention and treatment of human diseases.

The non-canonical effects of heme oxygenase-1, a classical fighter against oxidative stress

The role of heme oxygenase-1 in resisting oxidative stress and cell protection has always been a hot research topic. With the continuous deepening of research, in addition to directly regulating redox by catalyzing the degradation of heme, HO-1 protein also participates in the gene expression level in a great diversity of methods, thereby initiating cell defense. Particularly the non-canonical nuclear-localized HO-1 and HO-1 protein interactions play the role of a warrior against oxidative stress. Besides, HO-1 may be a promising marker for disease prediction and detection in many clinical trials. Especially for malignant diseases, there may be new advances in the treatment of HO-1 by regulating abnormal ROS and metabolic signaling. The purpose of this review is to systematically sort out and describe several aspects of research to facilitate further detailed mechanism research and clinical application promotion in the future.

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The different subcellular localizations ofHO-1 implies that it has special functions.

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Nuclear HO-1 plays an indispensable role in gene regulation and other aspects.

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The interactions between HO-1 and others provide the possibility to participate in vital physiological processes.

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HO-1 may become a potential disease assessment marker.

Nuclear Localization of Heme Oxygenase-1 in Pathophysiological Conditions: Does It Explain the Dual Role in Cancer?

Heme Oxygenase-1 (HO-1) is a type II detoxifying enzyme that catalyzes the rate-limiting step in heme degradation leading to the formation of equimolar quantities of carbon monoxide (CO), free iron and biliverdin. HO-1 was originally shown to localize at the smooth endoplasmic reticulum membrane (sER), although increasing evidence demonstrates that the protein translocates to other subcellular compartments including the nucleus. The nuclear translocation occurs after proteolytic cleavage by proteases including signal peptide peptidase and some cysteine proteases. In addition, nuclear translocation has been demonstrated to be involved in several cellular processes leading to cancer progression, including induction of resistance to therapy and enhanced metastatic activity. In this review, we focus on nuclear HO-1 implication in pathophysiological conditions with special emphasis on malignant processes. We provide a brief background on the current understanding of the mechanisms underlying how HO-1 leaves the sER membrane and migrates to the nucleus, the circumstances under which it does so and, maybe the most important and unknown aspect, what the function of HO-1 in the nucleus is.