The Ubiquitin E3 Ligase TRAF6 Exacerbates Ischemic Stroke by Ubiquitinating and Activating Rac1

Dysregulated SYVN1 promotes CAV1 protein ubiquitination and accentuates ischemic stroke

BACKGROUND

Stroke is a major cause of death and severe disability, and there remains a substantial need for the development of therapeutic agents for neuroprotection in acute ischemic stroke (IS) to protect the brain against damage before and during recanalization. Caveolin-1 (CAV1), an integrated protein that is located at the caveolar membrane, has been reported to exert neuroprotective effects during IS. Nevertheless, the mechanism remains largely unknown. Here, we explored the upstream modifiers of CAV1 in IS.

METHODS

E3 ubiquitin ligases of CAV1 that are differentially expressed in IS were screened using multiple databases. The transcription factor responsible for the dysregulation of E3 ubiquitin-protein ligase synoviolin (SYVN1) in IS was predicted and verified. Genetic manipulations by lentiviral vectors were applied to investigate the effects of double-strand-break repair protein rad21 homolog (RAD21), SYVN1, and CAV1 in a middle cerebral artery occlusion (MCAO) mouse model and mouse HT22 hippocampal neurons induced by oxygen-glucose deprivation (OGD).

RESULTS

SYVN1 was highly expressed in mice with MCAO, and knockdown of SYVN1 alleviated IS injury in mice, as evidenced by limited infarction volume, the lower water content in the brain, and repressed apoptosis and inflammatory response. RAD21 inhibited the transcription of SYVN1, thereby reducing the ubiquitination modification of CAV1. Overexpression of RAD21 elicited a neuroprotective role as well in mice with MCAO and HT22 induced with OGD, which was overturned by SYVN1.

CONCLUSION

Transcriptional repression of SYVN1 by RAD21 alleviates IS in mice by reducing ubiquitination modification of CAV1.

Inhibition of esophageal cancer progression through HACE1-TRIP12 interaction and associated RAC1 ubiquitination and degradation

Objective: This study investigated the significance of HECT domain and ankyrin repeat containing E3 ubiquitin protein ligase 1 (HACE1) in esophageal cancer (ESCA) and its underlying mechanism in ESCA regulation through the induction of RAC1 ubiquitination and degradation. Methods: Characterization studies of HACE1 in ESCA clinical tissues and cell lines were performed. Next, the effects of HACE1 on the biological behavior of ESCA cells were examined by silencing and overexpressing HACE1. Protein-protein interactions (PPIs) involving HACE1 were analyzed using data from the String website. The function of HACE1 in RAC1 protein ubiquitination was validated using the proteasome inhibitor MG132. The effects of HACE1 on ESCA cells through RAC1 were elucidated by applying the RAC1 inhibitor EHop-016 in a tumor-bearing nude mouse model. To establish the relationship between HACE1 and TRIP12, rescue experiments were conducted, mainly to evaluate the effect of TRIP12 silencing on HACE1-mediated RAC1 regulation in vitro and in vivo. The PPI between HACE1 and TRIP12 and their subcellular localization were further characterized through co-immunoprecipitation and immunofluorescence staining assays, respectively. Results: HACE1 protein expression was notably diminished in ESCA cells but upregulated in normal tissues. HACE1 overexpression inhibited the malignant biological behavior of ESCA cells, leading to restrained tumor growth in mice. This effect was coupled with the promotion of RAC1 protein ubiquitination and subsequent degradation. Conversely, silencing HACE1 exhibited contrasting results. PPI existed between HACE1 and TRIP12, compounded by their similar subcellular localization. Intriguingly, TRIP12 inhibition blocked HACE1-driven RAC1 ubiquitination and mitigated the inhibitory effects of HACE1 on ESCA cells, alleviating tumor growth in the tumor-bearing nude mouse model. Conclusion: HACE1 expression was downregulated in ESCA cells, suggesting that it curbs ESCA progression by inducing RAC1 protein degradation through TRIP12-mediated ubiquitination.

MiR-31-5p regulates the neuroinflammatory response via TRAF6 in neuropathic pain

BACKGROUND

Neuropathic pain is chronic pain and has few effective control strategies. Studies have demonstrated that microRNAs have functions in neuropathic pain. However, no study has been conducted to demonstrate the role and mechanism of microRNA (miR)-31-5p in neuropathic pain. Accordingly, this study sought to determine the pathological role of miR-31-5p in chronic constriction injury (CCI) -induced neuropathic pain mouse models.

METHODS

We used CCI surgery to establish mouse neuropathic pain model. Behavioral tests were performed to evaluate pain sensitivity of mice. Expressions of miR-31-5p and inflammatory cytokines in dorsal root ganglion (DRG) were examined by polymerase chain reaction. Animals or cells were received with/without miR-31-5p mimic or inhibitor to investigate its role in neuropathic pain. The mechanism of miR-31-5p was assayed using western blotting, immunofluorescence staining and dual-luciferase reporter assay.

RESULTS

We found that CCI led to a significant decrease in miR-31-5p levels. Knockout of miR-31-5p and administration of miPEP31 exacerbated pain in C57BL/6 mice. Meanwhile, miR-31-5p overexpression increased the paw withdrawal threshold and latency. TRAF6 is one of the target gene of miR-31-5p, which can trigger a complex inflammatory response. TRAF6 was associated with pain and that reducing the DRG expression of TRAF6 could alleviate pain. In addition, miR-31-5p overexpression inhibited the TRAF6 expression and reduced the neuroinflammatory response.

CONCLUSIONS

All the results reveal that miR-31-5p could potentially alleviate pain in CCI mouse models by inhibiting the TRAF6 mediated neuroinflammatory response. MiR-31-5p upregulation is highlighted here as new target for CCI treatment.

The HACE1 E3 ligase mediates RAC1-dependent control of mTOR signaling complexes

HACE1 is a HECT family E3 ubiquitin-protein ligase with broad but incompletely understood tumor suppressor activity. Here, we report a previously unrecognized link between HACE1 and signaling complexes containing mammalian target of rapamycin (mTOR). HACE1 blocks mTORC1 and mTORC2 activities by reducing mTOR stability in an E3 ligase-dependent manner. Mechanistically, HACE1 binds to and ubiquitylates Ras-related C3 botulinum toxin substrate 1 (RAC1) when RAC1 is associated with mTOR complexes, including at focal adhesions, leading to proteasomal degradation of RAC1. This in turn decreases the stability of mTOR to reduce mTORC1 and mTORC2 activity. HACE1 deficient cells show enhanced mTORC1/2 activity, which is reversed by chemical or genetic RAC1 inactivation but not in cells expressing the HACE1-insensitive mutant, RAC1K147R . In vivo, Rac1 deletion reverses enhanced mTOR expression in KRasG12D -driven lung tumors of Hace1-/- mice. HACE1 co-localizes with mTOR and RAC1, resulting in RAC1-dependent loss of mTOR protein stability. Together, our data demonstrate that HACE1 destabilizes mTOR by targeting RAC1 within mTOR-associated complexes, revealing a unique ubiquitin-dependent process to control the activity of mTOR signaling complexes.

Sirtuins: Promising Therapeutic Targets to Treat Ischemic Stroke

Stroke is a major cause of mortality and disability globally, with ischemic stroke (IS) accounting for over 80% of all stroke cases. The pathological process of IS involves numerous signal molecules, among which are the highly conserved nicotinamide adenine dinucleotide (NAD+)-dependent enzymes known as sirtuins (SIRTs). SIRTs modulate various biological processes, including cell differentiation, energy metabolism, DNA repair, inflammation, and oxidative stress. Importantly, several studies have reported a correlation between SIRTs and IS. This review introduces the general aspects of SIRTs, including their distribution, subcellular location, enzyme activity, and substrate. We also discuss their regulatory roles and potential mechanisms in IS. Finally, we describe the current therapeutic methods based on SIRTs, such as pharmacotherapy, non-pharmacological therapeutic/rehabilitative interventions, epigenetic regulators, potential molecules, and stem cell-derived exosome therapy. The data collected in this study will potentially contribute to both clinical and fundamental research on SIRTs, geared towards developing effective therapeutic candidates for future treatment of IS.

A comprehensive analysis of the hub genes for oxidative stress in ischemic stroke

Ischemic stroke (IS), resulting from the occlusion of the cerebral artery and subsequent interruption of blood flow, represents a major and critical threat to public health. Oxidative stress (OS) has been confirmed to play a role in the IS pathological process and neural death. Understanding the essential role of OS-related genes in ischemic stroke is critical to understanding the current perception of the pathophysiological process in IS. Herein, by integrating three IS datasets (GSE16561, GSE22255, and GSE58294), we divided IS samples into the low- and high-OS groups by calculating the OS score identified by the oxidative stress gene set. The functional enrichment analysis of differentially expressed genes (DEGs) between the low- and high-OS groups indicated that DEGs were associated with hypoxia, the inflammatory response, and oxidative phosphorylation pathways. Furthermore, nine hub genes (namely TLR1, CXCL1, MMP9, TLR4, IL1R2, EGR1, FOS, CXCL10, and DUSP1) were identified through the Girvan-Newman algorithm and cytoHubba algorithms. Nine hub genes were highly expressed in IS samples and positively related to neutrophils and macrophages. Drug-sensitive analysis targeting hub genes defined allopurinol and nickel sulfate as potential candidates for impairing the neural death caused by oxidative stress in IS. Finally, we employed five machine learning methods to check the efficacy of the predictive model identified by nine hub genes. The results showed that our model had superior power for predicting the OS activity of IS patients. TLR4 was found to have excellent diagnostic value and a wide-spectrum interaction with other hub genes. Our research emphasized the impact of oxidative stress on ischemic stroke, which supports the idea that antioxidants hold great promise in ischemic stroke therapy.

Astrocytes-derived exosomes pre-treated by berberine inhibit neuroinflammation after stroke via miR-182-5p/Rac1 pathway

BACKGROUND

Our previous studies have shown that berberine can improve the nerve function deficits in ischemic stroke by inhibiting inflammation. The cellular communication between astrocytes and neurons via exosomes might affect neurological function after ischemic stroke, which plays a vital role in the therapy of ischemic stroke.

OBJECTIVE

The present study focused on the effects of exosomes released from astrocytes induced by the glucose and oxygen deprivation model with berberine pretreatment (BBR-exos) treatment for ischemic stroke and its regulatory mechanism.

METHODS

Oxygen-glucose-deprivation/Reoxygenation (OGD/R)-treated primary cells were used to mimic cerebral ischemia/reperfusion conditions in vitro. With the treatment of BBR-exos and exosomes released from primary astrocytes induced by the glucose and oxygen deprivation model (OGD/R-exos), the cell viability was detected. C57BL/6J mice were used to establish middle cerebral artery occlusion/reperfusion (MCAO/R) model. The anti-neuroinflammation effects of BBR-exos and OGD/R-exos were evaluated. Subsequently, the key miRNA in BBR-exos was identified by exosomal miRNA sequencing and cell validation. miR-182-5p mimic and inhibitors were provided to verify the effects in inflammation. Finally, the binding sites between miR-182-5p and Rac1 were predicted online and verified by using a dual-luciferase reporter assay.

RESULTS

BBR-exos and OGD/R-exos both improved the decreased activity of OGD/R-induced neurons, and decreased the expression of IL-1β, IL-6 and TNF-α (all P ＜ 0.05), which reduced neuronal injury and inhibited neuroinflammation in Vitro. And BBR-exos showed better effects (P ＜ 0.05). The same effect has been verified in vivo experiments: BBR-exos and OGD/R-exos both reduced cerebral ischemic injury and inhibited neuroinflammation in MCAO/R mice (all P ＜ 0.05). Likewise, BBR-exos showed better effects (P ＜ 0.05). The exosomal miRNA sequencing results showed that miR-182-5p was highly expressed in BBR-exos and inhibited neuroinflammation by targeting Rac1 (P ＜ 0.05).

CONCLUSION

BBR-exos can carry miR-182-5p to injured neurons and inhibit the expression of Rac1, which could inhibit neuroinflammation and improved brain injury after ischemic stroke.

IKK-mediated TRAF6 and RIPK1 interaction stifles cell death complex assembly leading to the suppression of TNF-α-induced cell death

Tumor necrosis factor α (TNF-α) is a pro-inflammatory cytokine capable of inducing extrinsic apoptosis and necroptosis. Tumor necrosis factor receptor-associated factor 6 (TRAF6), an E3 ligase, is a member of the TRAF family of proteins, which mediates inflammatory signals by activating nuclear factor kappa B (NFкB) and mitogen-activated protein kinase (MAPK). Although the functions of TRAF6 have been identified, its role in TNF-α-induced cell death remains poorly understood. Here, we report that TRAF6 is a negative modulator of TNF-α-induced cell death but does not affect TNF-α-induced NFκB activation. TRAF6 deficiency accelerates both TNF-α-induced apoptosis and necroptosis; however, the acceleration can be reversed by reconstituting TRAF6 or TRAF6^C70A, suggesting that E3 ligase activity is not required for this activity. Mechanistically, TRAF6 directly interacts with RIPK1 during TNF-α-induced cell death signaling, which prevents RIPK1 from interacting with components of the cell death complex such as itself, FADD or RIPK3. These processes suppress the assembly of the death complex. Notably, IKK was required for TRAF6 to interact with RIPK1. In vivo, Traf6^-/- embryos exhibited higher levels of cell death in the liver but could be rescued by the simultaneous knockout of Tnf. Finally, TRAF6 knockdown xenografts were highly sensitive to necroptotic stimuli. We concluded that TRAF6 suppresses TNF-α-induced cell death in coordination with IKK complexes in vivo and in vitro by suppressing the assembly of cell death complex.

Carnosol inhibits cerebral ischemia-reperfusion injury by promoting AMPK activation

BACKGROUND

Carnosol is a phytopolyphenol (diterpene) found and extracted from plants of Mediterranean diet, which has anti-tumor, anti-inflammatory and antioxidant effects. However, its role in ischemic stroke has not been elucidated.

METHODS

Primary neurons subjected to oxygen-glucose deprivation (OGD) was used to investigate the effect of carnosol in vitro. A mouse MCAO model was used to evaluate the effect of carnosol on ischemic stroke in vivo. The mRNA level of inflammatory and apoptosis-related genes was determined by RT-PCR. The protein level of total and phosphorylated AMPK was determined by WB. H&E and Immunofluorescent assay was used to investigate the necrosis, inflammation and apoptosis in brain tissue.

RESULTS

Carnosol protected the activity of primary neurons subjected to oxygen-glucose deprivation (OGD) in vitro, as well as inhibited inflammation and apoptosis. Furthermore, carnosol could significantly reduce the infarct and edema volume and protect against neurological deficit in vivo, and had a significant inhibitory effect on brain neuroinflammation and apoptosis. Mechanically, carnosol could activate AMPK, and the effect of carnosol on cerebral ischemia-reperfusion injury cell model could be abolished by AMPK phosphorylation inhibitor.

CONCLUSION

Carnosol has a protective effect on ischemic stroke, and this effect is achieved through AMPK activation. Our study demonstrates the protective effect of carnosol on cerebral ischemia-reperfusion injury and provides a new perspective for the clinical treatment of ischemic stroke.

Purpurogallin Reverses Neuronal Apoptosis and Enhances "M2" Polarization of Microglia Under Ischemia via Mediating the miR-124-3p/TRAF6/NF-κB Axis

Purpurogallin (PPG) has been demonstrated to exert an anti-inflammatory function in neurological diseases. This study aimed at investigating the role of PPG on microglial polarization post ischemic stroke as well as the underlying mechanism. Mouse hippocampal neurons HT-22 and microglial BV2 cells were treated by oxygen and glucose deprivation to simulate an in-vitro ischemia model. qRT-PCR and ELISA examined expression of cytokines in microglia. CCK8 and flow cytometry measured HT-22 cell viability and apoptosis, respectively. The levels of miR-124-3p and TRAF6/NF-κB were determined. A mouse cerebral ischemia model was set up using middle cerebral artery occlusion (MCAO) method. After being dealt with PPG, the neurological functions, brain edema, neuronal apoptosis, and microglia activation of the mice were evaluated. As suggested by the results, PPG transformed "M1" to "M2" polarization of BV2 cells, and abated HT-22 cell apoptosis. PPG enhanced the neurological functions, alleviated brain edema, and decreased neuroinflammatory responses, and neuronal apoptosis in the brain lesions of MCAO mice. Furthermore, PPG enhanced miR-124-3p and repressed the TRAF6/NF-κB pathway. miR-124-3p suppressed the TRAF6/NF-κB pathway by targeting TRAF6. Collectively, PPG alleviates ischemia-induced neuronal damage and microglial inflammation by modulating the miR-124-3p/TRAF6/NF-κB pathway.

PHLDA1 promotes sevoflurane-induced pyroptosis of neuronal cells in developing rats through TRAF6-mediated activation of Rac1

Sevoflurane anesthesia induces neurocognitive impairment and pyroptosis in the developing brain. Pleckstrin homology-like domain, family A, member 1 (PHLDA1) was involved in neuronal apoptosis, oxidative stress and inflammation during ischemic stroke. The role of PHLDA1 in sevoflurane-induced pyroptosis in developing rats was investigated. Firstly, neonatal rats at day 7 was exposed to 2.0% sevoflurane for 6 h to induce neurotoxicity. Pathological analysis showed that sevoflurane anesthesia induced hippocampal injury and reduced the number of neurons. The expression of PHLDA1 was elevated in hippocampus of sevoflurane-treated rats. Secondly, sevoflurane anesthesia-treated neonatal rats were injected with adeno-associated virus serotype (AAV) to mediate knockdown of PHLDA1. Injection with AAV-shPHLDA1 ameliorated sevoflurane-induced hippocampal injury and neurocognitive impairment in rats. Moreover, knockdown of PHLDA1 increased the number of neurons in sevoflurane-treated rats. Silence of PHLDA1 suppressed neuronal apoptosis, and inhibited pyroptosis in sevoflurane-treated rats. Thirdly, PHLDA1 was also elevated in sevoflurane-treated primary neuronal cells. Loss of PHLDA1 also enhanced cell viability and suppressed pyroptosis of sevoflurane-treated primary neuronal cells. Lastly, silence of PHLDA1 reduced protein expression of TRAF6 and p-Rac1 in sevoflurane-treated rats and neuronal cells. Over-expression of TRAF6 attenuated PHLDA1 silence-induced increase of cell viability and decreased pyroptosis in neuronal cells. In conclusion, loss of PHLDA1 protected against sevoflurane-induced pyroptosis in developing rats through inhibition of TRAF6-mediated activation of Rac1.

Chrysophanol postconditioning attenuated cerebral ischemia-reperfusion injury induced NLRP3-related pyroptosis in a TRAF6-dependent manner

Individuals who suffer from post-CA (cardiac arrest) brain injury experience higher mortality and more severe functional disability. Neuroinflammation has been identified as a vital factor in cerebral ischemia-reperfusion injury (CIRI) following CA. Pyroptosis induces neuronal death by triggering an excessive inflammatory injury. Chrysophanol possesses robust anti-inflammatory features, and it is protective against CIRI. The purpose of this research was to assess the effect of Chrysophanol postconditioning on CIRI-induced pyroptotic cell death, and to explore its underlying mechanisms. CIRI was induced in rats by CA and subsequent cardiopulmonary resuscitation, and PC12 cells were exposed to oxygen-glucose deprivation/reoxygenation (OGD/R) to imitate CIRI in vitro. It was found that post-CA brain injury led to a notable cerebral damage revealed by histopathological changes and neurological outcomes. The existence of pyroptosis was also confirmed in in vivo and in vitro CIRI models. Moreover, we further confirmed that Chrysophanol, the main bioactive ingredient of Rhubarb, significantly suppressed expressions of pyroptosis-associated proteins, e.g., NLRP3, ASC, cleaved-caspase-1 and N-terminal GSDMD, and inhibited the expression of tumor necrosis factor receptor-associated factor 6 (TRAF6). Furthermore, NLRP3 overexpression neutralized the neuroprotection of Chrysophanol postconditioning, suggesting that pyroptosis was the major neuronal death pathway modulated by Chrysophanol postconditioning in OGD/R. Additionally, the neuroprotection of Chrysophanol postconditioning was also abolished by gain-of-function analyses of TRAF6. Finally, the results demonstrated that Chrysophanol postconditioning suppressed the interaction between TRAF6 and NLRP3. Taken together, our findings revealed that Chrysophanol postconditioning was protective against CIRI by inhibiting NLRP3-related pyroptosis in a TRAF6-dependent manner.

The E3 ubiquitin ligase MG53 inhibits hepatocellular carcinoma by targeting RAC1 signaling

Ras-related C3 botulinum toxin substrate 1 (RAC1) overexpressiosn and hyperactivation are correlated with aggressive growth and other malignant characteristics in a wide variety of cancers including hepatocellular carcinoma (HCC). However, the regulatory mechanism of RAC1 expression and activation in HCC is not fully understood. Here, we demonstrated that E3 ubiquitin ligase MG53 (also known as tripartite motif 72, TRIM72) acted as a direct inhibitor of RAC1, and it catalyzed the ubiquitination of RAC1 and further inhibited RAC1 activity in HCC cells. Mechanistically, MG53 directly bound with RAC1 through its coiled-coil domain and suppressed RAC1 activity by catalyzing the Lys48 (K48)-linked polyubiquitination of RAC1 at Lys5 residue in HCC cells. We further demonstrated that MG53 significantly suppressed the malignant behaviors of HCC cells and enhanced the chemosensitivity of HCC cells to sorafenib treatment by inhibiting RAC1-MAPK signaling axis. In summary, we identified MG53 as a novel RAC1 inhibitor and tumor suppressor in HCC, and it suppressed HCC progression by inducing K48-linked polyubiquitination of RAC1 and further inhibiting the RAC1-MAPK signaling. Altogether, our investigation provided a new therapeutic strategy for RAC1 overactivated tumors by modulating MG53.

MicroRNA-124 attenuates PTSD-like behaviors and reduces the level of inflammatory cytokines by downregulating the expression of TRAF6 in the hippocampus of rats following single-prolonged stress

BACKGROUND

MicroRNA-124-3p (miR-124) plays an important role in neuroprotective functions in various neurological disorders, but whether miR-124 participates in the pathological progression of posttraumatic stress disorder (PTSD) remains poorly understood.

METHODS

In the present study, we assessed the level of neuroinflammation in the hippocampus of rats exposed to single-prolonged stress (SPS) by Western blot and immunofluorescence staining, while the effect of miR-124 on PTSD-like behaviors was evaluated by behavioral test.

RESULTS

Our results showed that the level of miR-124 in the hippocampus of rats exposed to SPS was downregulated and that the upregulation of miR-124 could alleviate the PTSD-like behaviors of SPS rats. This effect of miR-124 might be achieved through TNF receptor-associated Factor 6 (TRAF6), which is a target gene of miR-124 and plays an important role in the immune and inflammatory reaction by regulating nuclear factor kappa-B (NF-κB). Furthermore, we found that miR-124 not only decreased the level of proinflammatory cytokines but also increased the expression levels of synaptic proteins (PSD95 and synapsin I) and regulated the morphology of neurons.

CONCLUSION

These results suggested that miR-124 might attenuate PTSD-like behaviors and decrease the level of proinflammatory cytokines by downregulating the expression of TRAF6 in the hippocampus of rats exposed to SPS.

Neuroprotective Effect of E3 Ubiquitin Ligase RNF8 Against Ischemic Stroke via HDAC2 Stability Reduction and Reelin-Dependent GSK3β Inhibition

Loss of E3 ubiquitin ligase RING finger protein 8 (RNF8) may lead to neuronal DNA damage and apoptosis. In order to expand on our knowledge on the mechanistic basis underlying neuronal death in ischemic stroke, the present study sought to investigate the potential role of E3 ubiquitin ligase RNF8 on ischemic stroke and explore the underlying downstream mechanism. Middle cerebral artery occlusion (MCAO) in mice and oxygen–glucose deprivation/reoxygenation (OGD/R) in neurons were induced to simulate an ischemic stroke environment. It was found that downregulation of RNF8 and Reelin occurred in MCAO mice and OGD/R-exposed neurons. Silencing of RNF8 enhanced the MCAO-induced neuronal apoptosis and oxidative stress. Mechanistically, RNF8 enhanced the ubiquitination and degradation of HDAC2, thus attenuating OGD/R-induced neuronal apoptosis and oxidative stress. Moreover, HDAC2 inhibited Reelin expression through deacetylation of H3K27me3 in its promoter, causing reduced glycogen synthase kinase-3beta (GSK3β)-Ser9 phosphorylation and the resultant elevated GSK3β activity. By this mechanism, RNF8 alleviated ischemic stroke. Coherently, this study suggests that RNF8 plays a neuroprotective effect against ischemic stroke by downregulating HDAC2 expression and inducing Reelin-induced GSK3β inhibition.

TRAF6 Suppresses the Development of Pulmonary Fibrosis by Attenuating the Activation of Fibroblasts

Pulmonary fibrosis (PF) has a high mortality rate, and its pathogenesis is unknown. TNF receptor-associated factor 6 (TRAF6), a signal transducer for inflammatory signaling, plays crucial roles in the pathogenesis of immune diseases. However, its function in PF remains unknown. Herein, we demonstrated that lungs from mice with bleomycin (BLM)-induced PF were characterized by decreased expression of TRAF6 in lung fibroblasts. Enhancing TRAF6 expression protected mice from BLM-induced PF coupled with a significant reduction in fibroblast differentiation. Furthermore, we demonstrated that overexpression of TRAF6 reversed the activation of myofibroblasts from PF mice by reducing the expression of Wnt3a and subsequently suppressing Wnt/β-catenin signaling. Additionally, the abundance of Tribbles pseudokinase 3 (TRIB3), a stress sensor, was negatively correlated with the abundance of TRAF6 in lung fibroblasts. TRIB3 overexpression decreased TRAF6 abundance by reducing TRAF6 stability in lung fibroblasts during PF. Mechanistic studies revealed that TRIB3 bound to TRAF6 and accelerated basal TRAF6 ubiquitination and degradation. Collectively, our data indicate that reduced TRAF6 expression in fibroblasts is essential for the progression of PF, and therefore, genetically increasing TRAF6 expression or disrupting the TRIB3-TRAF6 interaction could be potential therapeutic strategies for fibroproliferative lung diseases in clinical settings.

FAM49B, restrained by miR-22, relieved hepatic ischemia/reperfusion injury by inhibiting TRAF6/IKK signaling pathway in a Rac1-dependent manner

Hepatic ischemia/reperfusion (I/R) injury plays a pivotal pathogenic role in trauma, hepatectomy, and liver transplantation. However, the whole mechanism remains undescribed. The objective of this study is to investigate the internal mechanism by which microRNA-22 (miR-22) targets family with sequence similarity 49 member B (FAM49B), thus aggravating hepatic I/R injury. Here, we found that miR-22 was upregulated while FAM49B was reduced in hepatic I/R injury. Inhibition of miR-22 in vitro was able to intensify expression of FAM49B, thus reducing phosphorylation of inhibitors of nuclear factor kappa-B kinase (IKK) and downstream pro-inflammatory proteins. A dual luciferase reporter assay indicated that miR-22 directly targeted FAM49B. Remission of hepatic pathologic alterations, apoptosis, and release of cytokines derived from constraints of miR-22 were abolished in vivo by repressing FAM49B. Further interference of Ras-related C3 botulinum toxin substrate 1 (Rac1) reversed the function of FAM49B inhibition, thus achieving anti-inflammatory consequences.

Bone marrow mesenchymal stem cells-derived exosomal microRNA-124-3p attenuates hypoxic-ischemic brain damage through depressing tumor necrosis factor receptor associated factor 6 in newborn rats

Mesenchymal stem cells (MSCs)-derived exosomes (Exo) are beneficial in the use of brain damages. Restrictively, the mechanism of Exo expressing miR-124-3p in hypoxic-ischemic brain damage (HIBD) is not completely comprehended. Thereupon, this work was put forward to reveal the action of bone marrow MSCs-derived Exo (BMSCs-Exo) expressing miR-124-3p in the illness. BMSCs were isolated and transfected with miR-124-3p agomir. Then, BMSCs-Exo were extracted and identified. The newborn HIBD rats were injected with miR-124-3p-modified BMSCs-Exo or tumor necrosis factor receptor associated factor 6 (TRAF6)-related vectors. Next, neurological functions, neuron pathological and structural damages, oxidative stress and neuronal apoptosis were observed. miR-124-3p and TRAF6 expression was tested, along with their targeting relationship. miR-124-3p was down-regulated, and TRAF6 was up-regulated in newborn HIBD rats. miR-124-3p targeted TRAF6. BMSCs-Exo improved neurological functions, alleviated neuron pathological and structural damages, suppressed oxidative stress and reduced neuronal apoptosis in newborn HIBD rats, whereas BMSCs-Exo-mediated effects were enhanced by restoring miR-124-3p. Silencing TRAF6 attenuated HIBD in newborn rats, but overexpression of TRAF6 reversed the protective role of miR-124-3p-overexpressing BMSCs-Exo. This work makes it comprehensive that up-regulated exosomal miR-124-3p ameliorates HIBD in newborn rats by targeting TRAF6, which replenishes the potential agents for curing HIBD.

GPS-Uber: a hybrid-learning framework for prediction of general and E3-specific lysine ubiquitination sites

As an important post-translational modification, lysine ubiquitination participates in numerous biological processes and is involved in human diseases, whereas the site specificity of ubiquitination is mainly decided by ubiquitin-protein ligases (E3s). Although numerous ubiquitination predictors have been developed, computational prediction of E3-specific ubiquitination sites is still a great challenge. Here, we carefully reviewed the existing tools for the prediction of general ubiquitination sites. Also, we developed a tool named GPS-Uber for the prediction of general and E3-specific ubiquitination sites. From the literature, we manually collected 1311 experimentally identified site-specific E3-substrate relations, which were classified into different clusters based on corresponding E3s at different levels. To predict general ubiquitination sites, we integrated 10 types of sequence and structure features, as well as three types of algorithms including penalized logistic regression, deep neural network and convolutional neural network. Compared with other existing tools, the general model in GPS-Uber exhibited a highly competitive accuracy, with an area under curve values of 0.7649. Then, transfer learning was adopted for each E3 cluster to construct E3-specific models, and in total 112 individual E3-specific predictors were implemented. Using GPS-Uber, we conducted a systematic prediction of human cancer-associated ubiquitination events, which could be helpful for further experimental consideration. GPS-Uber will be regularly updated, and its online service is free for academic research at http://gpsuber.biocuckoo.cn/.

Benzoyl‑xanthone derivative induces apoptosis in MCF‑7 cells by binding TRAF6

TNF receptor-associated factor 6 (TRAF6) has been reported to be associated with the development of cancer. Nevertheless, the exact role of TRAF6 in cancer remains unclear. The purpose of the present study was to explore the mechanism of 2-benzoyl-3-hydroxy-4-methyl-9H-xanthen-9-one leading to the inhibition of the activation of AKT and TGF-β-activated kinase 1 (TAK1), and to the apoptosis of MCF-7 cells. Using a computational docking program and examination of AKT and TAK1 level changes, a new small molecule was identified, 2-benzoyl-3-hydroxy-4-methyl-9H-xanthen-9-one, which competitively bound to TRAF6. Next, the effect of this new compound on MCF-7 cells' biological behavior was studied in vitro. MTT assays were used to investigate cell viability; flow cytometry and invasion assays were performed to detect early apoptosis and invasion in MCF-7 cells, respectively. Immunoprecipitation, western blotting and caspase-3/9 activity assays were carried out to explore changes in protein expression. Briefly, the present data indicated that 2-benzoyl-3-hydroxy-4-methyl-9H-xanthen-9-one could suppress proliferation, induce early apoptosis and inhibit invasion in MCF-7 cells by suppressing the expression of Bcl-2 and promoting the expression of Bax, caspase-9, and caspase-3. These findings indicated that 2-benzoyl-3-hydroxy-4-methyl-9H-xanthen-9-one could induce apoptosis by inhibiting the activation of AKT and TAK1, and affecting the Bcl-2/Bax-caspase-9-caspase-3 pathway by competitively binding with TRAF6.

C5aR1 Mediates the Progression of Inflammatory Responses in the Brain of Rats in the Early Stage after Ischemia and Reperfusion

C5a receptor 1 (C5aR1) can induce a strong inflammatory response to an injury. Targeting C5aR1 has emerged as a novel anti-inflammatory therapeutic method. However, the role of C5aR1 in cerebral ischemia and reperfusion (I/R) injury and the definitive mechanism have not been elucidated clearly. Here, we determined whether C5aR1 signaling was essential to the post-ischemic inflammation and brain injury and whether it is a valid target for therapeutic blockade by using soluble receptor antagonist PMX53 in the early stage after I/R injury. In an in vitro model (oxygen and glucose deprivation and reperfusion, OGD/R) and in vivo model (middle cerebral artery occlusion and reperfusion, MCAO/R) of I/R, the neuronal cells of rats showed significantly up-regulated gene expression of C5aR1, and a notable inflammatory response was demonstrated with elevated tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6. Inhibition of C5aR1 by PMX53 treatment significantly reduced cell injury and inflammation and promoted brain function recovery. Further mechanism studies showed that inhibiting C5aR1 by PMX53 protected the rats from MCAO/R injury, decreased cell inflammation, and apoptosis via inhibiting the TLR4 and NF-κB signaling pathway and reducing the production of TNF-α, IL-1β, and IL-6 in MCAO/R rats. In addition, manipulation of the C5aR1 gene expression in vitro displayed that the inflammatory cascade signals including TLR4, TNF-α, IL-1β, and IL-6 were coincidently regulated with the regulation of C5aR1 expression levels. Thus, our results demonstrated a pathogenic role for C5aR1 in the progression of brain injury and inflammation response following I/R injury. Our study clearly demonstrated that C5aR1 inhibition might be an effective treatment strategy for ischemic stroke.

c-Myc affects hedgehog pathway via KCNQ1OT1/RAC1: A new mechanism for regulating HSC proliferation and epithelial-mesenchymal transition

BACKGROUND

This study aimed to probe into the potential mechanism of KCNQ1OT1 in liver fibrosis.

METHODS

The pathological changes in liver tissues were observed by Masson and hematoxylin-eosin (HE) staining. The proliferation or cell cycle of hepatic stellate cells (HSCs) was analyzed by MTT or flow cytometry. The expressions of epithelial markers E-cadherin, interstitial markers Snail and Vimentin, and hedgehog signaling pathway-related molecules Hhip, Shh, and Gli2 were detected by Western blot. The interaction or binding of c-Myc with the KCNQ1OT1 promoter was analyzed by dual-luciferase reporter gene or Chromatin immunoprecipitation (ChIP)-qPCR, and the interaction between KCNQ1OT1 and RAC1 was assessed by RNA immunoprecipitation and RNA pull-down. Moreover, the stability of RAC1 protein was detected by cycloheximide-chase and ubiquitination.

RESULTS

c-Myc and KCNQ1OT1 were up-regulated in liver fibrosis tissues and cells. After the interference with c-Myc in primary-1-Day HSCs, the down-regulated KCNQ1OT1 restrained HSC proliferation and EMT by down-regulating RAC1 expression and restraining the hedgehog pathway.

CONCLUSION

Our results indicated that the interference with c-Myc down-regulated RAC1 expression and restrained the hedgehog pathway by down-regulating KCNQ1OT1, thus restraining HSC proliferation and EMT in liver fibrosis.

Bioinformatic analysis for potential biological processes and key targets of heart failure-related stroke

This study aimed to uncover underlying mechanisms and promising intervention targets of heart failure (HF)-related stroke. HF-related dataset GSE42955 and stroke-related dataset GSE58294 were obtained from the Gene Expression Omnibus (GEO) database. Weighted gene co-expression network analysis (WGCNA) was conducted to identify key modules and hub genes. Gene Ontology (GO) and pathway enrichment analyses were performed on genes in the key modules. Genes in HF- and stroke-related key modules were intersected to obtain common genes for HF-related stroke, which were further intersected with hub genes of stroke-related key modules to obtain key genes in HF-related stroke. Key genes were functionally annotated through GO in the Reactome and Cytoscape databases. Finally, key genes were validated in these two datasets and other datasets. HF- and stroke-related datasets each identified two key modules. Functional enrichment analysis indicated that protein ubiquitination, Wnt signaling, and exosomes were involved in both HF- and stroke-related key modules. Additionally, ten hub genes were identified in stroke-related key modules and 155 genes were identified as common genes in HF-related stroke. OTU deubiquitinase with linear linkage specificity(OTULIN) and nuclear factor interleukin 3-regulated(NFIL3) were determined to be the key genes in HF-related stroke. Through functional annotation, OTULIN was involved in protein ubiquitination and Wnt signaling, and NFIL3 was involved in DNA binding and transcription. Importantly, OTULIN and NFIL3 were also validated to be differentially expressed in all HF and stroke groups. Protein ubiquitination, Wnt signaling, and exosomes were involved in HF-related stroke. OTULIN and NFIL3 may play a key role in HF-related stroke through regulating these processes, and thus serve as promising intervention targets.

The interplay of Rac1 activity, ubiquitination and GDI binding and its consequences for endothelial cell spreading

Signaling by the Rho GTPase Rac1 is key to the regulation of cytoskeletal dynamics, cell spreading and adhesion. It is widely accepted that the inactive form of Rac1 is bound by Rho GDI, which prevents Rac1 activation and Rac1-effector interactions. In addition, GDI-bound Rac1 is protected from proteasomal degradation, in line with data showing that Rac1 ubiquitination occurs exclusively when Rac1 is activated. We set out to investigate how Rac1 activity, GDI binding and ubiquitination are linked. We introduced single amino acid mutations in Rac1 which differentially altered Rac1 activity, and compared whether the level of Rac1 activity relates to Rac1 ubiquitination and GDI binding. Results show that Rac1 ubiquitination and the active Rac1 morphology is proportionally increased with Rac1 activity. Similarly, we introduced lysine-to-arginine mutations in constitutively active Rac1 to inhibit site-specific ubiquitination and analyze this effect on Rac1 signaling output and ubiquitination. These data show that the K16R mutation inhibits GTP binding, and consequently Rac1 activation, signaling and-ubiquitination, while the K147R mutation does not block Rac1 signaling, but does inhibits its ubiquitination. In both sets of mutants, no direct correlation was observed between GDI binding and Rac1 activity or -ubiquitination. Taken together, our data show that a strong, positive correlation exists between Rac1 activity and its level of ubiquitination, but also that GDI dissociation does not predispose Rac1 to ubiquitination.

Upregulated LINC00319 aggravates neuronal injury induced by oxygen-glucose deprivation via modulating miR-200a-3p

Ischemic stroke is one of the main causes of physical disability and mortality worldwide. Long non-coding RNAs (lncRNAs) are reported to be dysregulated in various biological progressions and serve important roles in pathological processes of cerebral ischemia. However, their biological actions and potential mechanisms in the progression of ischemic stroke remain unknown. The present study aimed to investigate the functions of LINC00319 on ischemic brain injury. It was identified that LINC00319 was significantly upregulated in the Gene Expression Omnibus profile of ischemic stroke. Furthermore, LINC00319 overexpression elevated caspase-3 activity and increased the apoptotic rate of neuronal cells, as well as decreased cell viability and glucose uptake. It was also demonstrated that LINC00319 participated in oxygen-glucose deprivation (OGD)-induced cerebral ischemic injury. LINC00319 could competitively bind with microRNA (miR)-200a-3p and decrease its expression. Moreover, miR-200a-3p could partly offset the negative effects of LINC00319 overexpression on neuronal injury caused by OGD. Collectively, the present results suggested that LINC00319 promoted apoptosis and aggravated neuronal injury induced by OGD by regulating miR-200a-3p, which may be important for ischemic stroke treatment.

RNF34 ablation promotes cerebrovascular remodeling and hypertension by increasing NADPH-derived ROS generation

Cerebrovascular remodeling is the most common cause of hypertension and stroke. Ubiquitin E3 ligase RING finger protein 34 (RNF34) is suggested to be associated with the development of multiple neurological diseases. However, the importance of RNF34 in cerebrovascular remodeling and hypertension is poorly understood. Herein, we used mice with a global RNF34 knockout as well as RNF34 floxed mice to delete RNF34 in endothelial cells and smooth muscle cells (SMCs). Our results showed that global RNF34 knockout mice substantially promoted angiotensin II (AngII)-induced middle cerebral artery (MCA) remodeling, hypertension, and neurological dysfunction. Endothelial cell RNF34 did not regulate the development of hypertension. Rather, SMC RNF34 expression is a critical regulator of hypertension and MCA remodeling. Loss of RNF34 enhanced AngII-induced mouse brain vascular SMCs (MBVSMCs) proliferation, migration and invasion. Furthermore, MCA and MBVSMCs from SMC RNF34-deficient mice showed increased superoxide anion and reactive oxygen species (ROS) generation as well as nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, but exhibited no marked effect on mitochondria-derived ROS. Knockout of RNF34 promoted p22^phox expression, leading to increased binding of p22^phox/p47^phox and p22^phox/NOX2, and eventually NADPH oxidase complex formation. Immunoprecipitation assay identified that RNF34 interacted with p22^phox. RNF34 deletion increased p22^phox protein stability by inhibiting ubiquitin-mediated degradation. Blockade of NADPH oxidase activity or knockdown of p22phox significantly abolished the effects of RNF34 deletion on cerebrovascular remodeling and hypertension. Collectively, our study demonstrates that SMC RNF34 deficiency promotes cerebrovascular SMC hyperplasia and remodeling by increased NADPH-derived ROS generation via reducing p22^phox ubiquitin-dependent degradation.

Pathogenic Functions of Tumor Necrosis Factor Receptor- Factor 6 Signaling Traumatic Brain Injury

Neuroinflammation contributes to delayed (secondary) neurodegeneration following traumatic brain injury (TBI). Tumor necrosis factor receptor-associated factor 6 (TRAF6) signaling may promote post-TBI neuroinflammation, thereby exacerbating secondary injury. This study investigated the pathogenic functions of TRAF6 signaling following TBI in vivo and in vitro. A rat TBI model was established by air pressure contusion while lipopolysaccharide (LPS) exposure was used to induce inflammatory-like responses in cultured astrocytes. Model rats were examined for cell-specific expression of TRAF6, NF-κB, phosphorylated (p)-NF-κB, MAPKs (ERK, JNK, and p38), p-MAPKs, chemokines (CCL2 and CXCL1), and chemokine receptors (CCR2 and CXCR2) by immunofluorescence, RT-qPCR, western blotting, and ELISA, for apoptosis by TUNEL staining, and spatial cognition by Morris water maze testing. These measurements were compared between TBI model rats receiving intracerebral injections of TRAF6-targeted RNAi vector (AAV9-TRAF6-RNAi), empty vector, MAPK/NF-κB inhibitors, or vehicle. Primary astrocytes were stimulated with LPS following TRAF6 siRNA or control transfection, and NF-κB, MAPKs, chemokine, and chemokine receptor expression levels evaluated by western blotting and ELISA. TRAF6 was expressed mainly in astrocytes and neurons of injured cortex, peaking 3 days post-TBI. Knockdown by AAV9-TRAF6-RNAi improved spatial learning and memory, decreased TUNEL-positive cell number in injured cortex, and downregulated expression levels of p-NF-κB, p-ERK, p-JNK, p-p38, CCL2, CCR2, CXCL1, and CXCR2 post-TBI. Inhibitors of NF-κB, ERK, JNK, and p38 significantly suppressed CCL2, CCR2, CXCL1, and CXCR2 expression following TBI. Furthermore, TRAF6-siRNA inhibited LPS-induced NF-κB, ERK, JNK, p38, CCL2, and CXCL1 upregulation in cultured astrocytes. Targeting TRAF6-MAPKs/NF-κB-chemokine signaling pathways may provide a novel therapeutic approach for reducing post-TBI neuroinflammation and concomitant secondary injury.

Combination of autophagy and NFE2L2/NRF2 activation as a treatment approach for neuropathic pain

Macroautophagy/autophagy, an evolutionarily conserved process, plays an important role in the regulation of immune inflammation and nervous system homeostasis. However, the exact role and mechanism of autophagy in pain is still unclear. Here, we showed that impaired autophagy flux mainly occurred in astrocytes during the maintenance of neuropathic pain. No matter the stage of neuropathic pain induction or maintenance, activation of autophagy relieved the level of pain, whereas inhibition of autophagy aggravated pain. Moreover, the levels of neuroinflammation and reactive oxygen species (ROS) were increased or decreased following autophagy inhibition or activation. Further study showed that inhibition of autophagy slowed the induction, but increased the maintenance of neuroinflammatory responses, which could be achieved by promoting the binding of TRAF6 (TNF receptor-associated factor 6) to K63 ubiquitinated protein, and increasing the levels of p-MAPK8/JNK (mitogen-activated protein kinase 8) and nuclear factor of kappa light polypeptide gene enhancer in B cells (NFKB/NF-κB). Impaired autophagy also reduced the protective effect of astrocytes on neurons against ROS stress because of the decrease in the level of glutathione released by astrocytes, which could be improved by activating the NFE2L2/NRF2 (nuclear factor, erythroid derived 2, like 2) pathway. We also demonstrated that simultaneous activation of autophagy and the NFE2L2 pathway further relieved pain, compared to activating autophagy alone. Our study provides an underlying mechanism by which autophagy participates in the regulation of neuropathic pain, and a combination of autophagy and NFE2L2 activation may be a new treatment approach for neuropathic pain.

Abbreviation: 3-MA: 3-methyladenine; 8-OHdG: 8-hydroxydeoxy-guanosine; ACTB: actin, beta; AMPAR: alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor; ATG: autophagy-related; CAMK2/CaMKII: calcium/calmodulin-dependent protein kinase II; CCL7: chemokine (C-C motif) ligand 7; CGAS: cyclic GMP-AMP synthase; CQ: chloroquine; GABA: gamma-aminobutyrate; GCLC: glutamate-cysteine ligase, catalytic subunit; GFAP: glial fibrillary acidic protein; GSH: glutathione; HMOX1/HO-1: heme oxygenase 1; KEAP1: kelch-like ECH-associated protein 1; MAP1LC3/LC3-II: microtubule-associated protein 1 light chain 3 beta (phosphatidylethanolamine-conjugated form); MAPK: mitogen-activated protein kinase; MAPK1/ERK: mitogen-activated protein kinase 1; MMP2: matrix metallopeptidase 2; MAPK8/JNK: mitogen-activated protein kinase 8; MAPK14/p38: mitogen-activated protein kinase 14; NFE2L2/NRF2: nuclear factor, erythroid derived 2, like 2; NFKB/NF-κB: nuclear factor of kappa light polypeptide gene enhancer in B cells; ROS: reactive oxygen species; SLC12A5: solute carrier family 12, member 5; SNL: spinal nerve ligation; TLR4: toll-like receptor 4; TRAF6: TNF receptor-associated factor; TRP: transient receptor potential.

Geranylgeranyl diphosphate synthase deficiency hyperactivates macrophages and aggravates lipopolysaccharide-induced acute lung injury

Macrophage activation is a key contributing factor for excessive inflammatory responses of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Geranylgeranyl diphosphate synthase (GGPPS) plays a key role in the development of inflammatory diseases. Our group previously showed that GGPPS in alveolar epithelium have deleterious effects on acute lung injury induced by LPS or mechanical ventilation. Herein, we examined the role of GGPPS in modulating macrophage activation in ALI/ARDS. We found significant increased GGPPS expression in alveolar macrophages in patients with ARDS compared with healthy volunteers and in ALI mice induced by LPS. GGPPS-floxed control (GGPPS^fl/fl) and myeloid-selective knockout (GGPPS^fl/flLysMcre) mice were then generated. Interestingly, using an LPS-induced ALI mouse model, we showed that myeloid-specific GGPPS knockout significantly increased mortality, aggravated lung injury, and increased the accumulation of inflammatory cells, total protein, and inflammatory cytokines in BALF. In vitro, GGPPS deficiency upregulated the production of LPS-induced IL-6, IL-1β, and TNF-α in alveolar macrophages, bone marrow-derived macrophages (BMDMs), and THP-1 cells. Mechanistically, GGPPS knockout increased phosphorylation and nuclear translocation of NF-κB p65 induced by LPS. In addition, GGPPS deficiency increased the level of GTP-Rac1, which was responsible for NF-κB activation. In conclusion, decreased expression of GGPPS in macrophages aggravates lung injury and inflammation in ARDS, at least partly by regulating Rac1-dependent NF-κB signaling. GGPPS in macrophages may represent a novel therapeutic target in ARDS.

USP30 protects against oxygen-glucose deprivation/reperfusion induced mitochondrial fragmentation and ubiquitination and degradation of MFN2

Cerebral ischemia-reperfusion induces mitochondrial fragmentation and dysfunction, which plays a critical role in the subsequent neuronal death and neurological impairment. Protection of mitochondria is an effective strategy to prevent neuronal damage after cerebral ischemia-reperfusion injury. USP30 is a deubiquitinating enzyme that localizes to the outer mitochondrial membrane. USP30 participates in the regulation of mitophagy and maintenance of mitochondrial morphology. In this study, the neuroprotective effect of USP30 and the underlying mechanisms were assessed in an ischemia-reperfusion injury model. SK-N-BE (2) cells were subjected to oxygen-glucose deprivation/reperfusion (OGDR) insult. Ubiquitination of mitochondrial proteins is increased during the early stage of reperfusion after oxygen-glucose deprivation (OGD), but the ubiquitination of cytoplasmic proteins exhibits no obvious changes. OGDR insult also induces rapid ubiquitination and degradation of the mitochondrial fusion protein mitofusin 2 (MFN2) in the early stage of reperfusion after OGD. Overexpression of MFN2 attenuates OGDR induced mitochondrial fragmentation. USP30 overexpression suppresses OGDR-induced ubiquitination and degradation of MFN2, and protects against mitochondrial fragmentation. Therefore, precisely targeting USP30 may provide a novel therapeutic strategy for cerebral ischemia-reperfusion related disorders.

miR-31 from adipose stem cell-derived extracellular vesicles promotes recovery of neurological function after ischemic stroke by inhibiting TRAF6 and IRF5

Ischemic stroke affects many people in the world, but the underlying mechanism is not completely understood. In this study, we investigated the effect of microRNA (miR)-31 on ischemic stroke. We also determined downstream signaling pathway of miR-31 in recovery of neurological function in ischemic stroke. Middle cerebral artery occlusion (MCAO) in mice was used to mimic human stroke. Foot fault test and mNSS were used to evaluate neurological deficits in mice after stroke. TTC staining in brain tissues was used for determining infarct volume. We extracted and identified extracellular vesicles (EVs) derived from adipose-derived stem cells (ADSCs) to study the impact of miR-31 and TRAF6 by miR-31 overexpression or TRAF6 knockdown on stroke recovery. Primary mouse neuron exposed to oxygen-glucose deprivation (OGD) was used to mimic neuronal ischemic injury. RT-qPCR and Western blot analysis were used for determination of mRNA and protein expression, respectively. MTT assay was used for studying cell survival. TUNEL staining was sued for neuron apoptosis. Starbase website and dual luciferase reporter gene assay were utilized to predicted and verify binding relationship between miR-31 and TRAF6. Neurological functions were improved by miR-31 from ADSC-derived EVs, as suggested by improved foot fault and mNSS. miR-31 from ADSC-derived EVs also reduced infarct volume and neuronal cell apoptosis after stroke in mice. Similarly, in neuronal cell culture, miR-31 from ADSC-derived EVs reduced the expression of apoptosis-related factors cleaved caspase-3 and Bax, increased the survival, and reduced apoptosis of neuronal cells after OGD. miR-31 was found to downregulate the expression of TRAF6 by binding to the 3'-untranslated region (3'-UTR) of TRAF6, which in turn upregulated IRF5 expression. Increased expression of IRF5 led to increased neuron apoptosis after OGD. In conclusion, miR-31 from ADSC-derived EVs can downregulate expression of TRAF6 and IRF5, leading to reduced neuronal damage induced by ischemic stroke.

Roles of TRAFs in Ischemia-Reperfusion Injury

Tumor necrosis factor receptor-associated factor (TRAF) proteins are a family of signaling molecules that function downstream of multiple receptor signaling pathways, and they play a pivotal role in the regulation of intracellular biological progresses. These TRAF-dependent signaling pathways and physiological functions have been involved in the occurrence and progression of ischemia-reperfusion injury (IRI), which is a common pathophysiological process that occurs in a wide variety of clinical events, including ischemic shock, organ transplantation, and thrombolytic therapy, resulting in a poor prognosis and high mortality. IRI occurs in multiple organs, including liver, kidney, heart, lung, brain, intestine, and retina. In recent years, mounting compelling evidence has confirmed that the genetic alterations of TRAFs can cause subversive phenotype changes during IRI of those organs. In this review, based on current knowledge, we summarized and analyzed the regulatory effect of TRAFs on the IRI of various organs, providing clear direction and a firm theoretical basis for the development of treatment strategies to manipulate TRAF proteins or TRAF-dependent signaling pathways in IRI-related diseases.

Wnt Pathway: An Emerging Player in Vascular and Traumatic Mediated Brain Injuries

The Wnt pathway, which comprises the canonical and non-canonical pathways, is an evolutionarily conserved mechanism that regulates crucial biological aspects throughout the development and adulthood. Emergence and patterning of the nervous and vascular systems are intimately coordinated, a process in which Wnt pathway plays particularly important roles. In the brain, Wnt ligands activate a cell-specific surface receptor complex to induce intracellular signaling cascades regulating neurogenesis, synaptogenesis, neuronal plasticity, synaptic plasticity, angiogenesis, vascular stabilization, and inflammation. The Wnt pathway is tightly regulated in the adult brain to maintain neurovascular functions. Historically, research in neuroscience has emphasized essentially on investigating the pathway in neurodegenerative disorders. Nonetheless, emerging findings have demonstrated that the pathway is deregulated in vascular- and traumatic-mediated brain injuries. These findings are suggesting that the pathway constitutes a promising target for the development of novel therapeutic protective and restorative interventions. Yet, targeting a complex multifunctional signal transduction pathway remains a major challenge. The review aims to summarize the current knowledge regarding the implication of Wnt pathway in the pathobiology of ischemic and hemorrhagic stroke, as well as traumatic brain injury (TBI). Furthermore, the review will present the strategies used so far to manipulate the pathway for therapeutic purposes as to highlight potential future directions.

Targeting CCL20 inhibits subarachnoid hemorrhage-related neuroinflammation in mice

Recent evidence suggests that CC chemokine ligand 20 (CCL20) is upregulated after subarachnoid hemorrhage (SAH). Here, we investigated the functions of CCL20 in SAH injury and its underlying mechanisms of action. We found that CCL20 is upregulated in an SAH mouse model and in cultured primary microglia and neurons. CCL20-neutralizing antibody alleviated SAH-induced neurological deficits, decreased brain water content and neuronal apoptosis, and repressed microglial activation. We observed increased levels of CCL20, CC chemokine receptor 6 (CCR6), interleukin 1 beta (IL-1β), and tumor necrosis factor alpha (TNF-α), as well as of microglial activation in microglia treated with oxyhemoglobin (OxyHb). CCL20 or CCR6 knockdown reversed the effects of OxyHb on microglia. Conditioned medium from OxyHb-treated microglia induced neuronal apoptosis, while the percentage of apoptotic neurons in the conditioned medium from microglia transfected with CCL20 siRNA or CCR6 siRNA was decreased. We observed no decrease in OxyHb-induced apoptosis in CCL20-knockdown neurons. Conditioned medium from OxyHb-treated neurons led to microglial activation and induced CCR6, IL-1β and TNF-α expression, while CCL20 knockdown in neurons or CCR6 knockdown in microglia reversed those effects. Our results thus suggest CCL20 may be targeted to elicit therapeutic benefits after SAH injury.

CARD3 Promotes Cerebral Ischemia-Reperfusion Injury Via Activation of TAK1

Background Although multiple signaling cascades and molecules contributing to the pathophysiological process have been studied, the treatments for stroke against present targets have not acquired significant clinical progress. Although CARD3 (caspase activation and recruitment domain 3) protein is an important factor involved in regulating immunity, inflammation, lipid metabolism, and apoptosis, its role in cerebral stroke is currently unknown. Methods and Results Using a mouse model of ischemia-reperfusion (I-R) injury based on transient blockage of the middle cerebral artery, we have found that CARD3 expression is upregulated in a time-dependent manner during I-R injury. Further animal study revealed that, relative to control mice, CARD3-knockout mice exhibited decreased inflammatory response and neuronal apoptosis, with reduced infarct volume and lower neuropathological scores. In contrast, neuron-specific CARD3-overexpressing transgenic (CARD3-TG) mice exhibited increased I-R induced injury compared with controls. Mechanistically, we also found that the activation of TAK1 (transforming growth factor-β-activated kinase 1) was enhanced in CARD3-TG mice. Furthermore, the increased inflammation and apoptosis seen in injured CARD3-TG brains were reversed by intravenous administration of the TAK1 inhibitor 5Z-7-oxozeaenol. Conclusions These results indicate that CARD3 promotes I-R injury via activation of TAK1, which not only reveals a novel regulatory axis of I-R induced brain injury but also provides a new potential therapeutic approach for I-R injury.

The Role of Ubiquitin-Proteasome Pathway and Autophagy-Lysosome Pathway in Cerebral Ischemia

The ubiquitin-proteasome pathway and autophagy-lysosome pathway are two major routes for clearance of aberrant cellular components to maintain protein homeostasis and normal cellular functions. Accumulating evidence shows that these two pathways are impaired during cerebral ischemia, which contributes to ischemic-induced neuronal necrosis and apoptosis. This review aims to critically discuss current knowledge and controversies on these two pathways in response to cerebral ischemic stress. We also discuss molecular mechanisms underlying the impairments of these protein degradation pathways and how such impairments lead to neuronal damage after cerebral ischemia. Further, we review the recent advance on the understanding of the involvement of these two pathways in the pathological process during many therapeutic approaches against cerebral ischemia. Despite recent advances, the exact role and molecular mechanisms of these two pathways following cerebral ischemia are complex and not completely understood, of which better understanding will provide avenues to develop novel therapeutic strategies for ischemic stroke.

RNF34 overexpression exacerbates neurological deficits and brain injury in a mouse model of intracerebral hemorrhage by potentiating mitochondrial dysfunction-mediated oxidative stress

Intracerebral hemorrhage (ICH) is a common neurological condition associated with high disability and mortality. Alterations in protein ubiquitination have emerged as a key mechanism in the pathogenesis of neurological diseases. Here, we investigated the effects of the E3 ubiquitin ligase ring finger protein 34 (RNF34) on neurological deficits and brain injury in ICH mice. An ICH model was established via intracerebral injection of autologous blood into wild-type and RNF34 transgenic mice. Brain injury, neurological function, neuronal activity, and oxidative stress levels were measured, respectively. The underlying mechanisms were explored by molecular and cellular approaches. Our results showed that RNF34 overexpression in mice significantly aggravated the ICH-induced memory impairment, brain edema, infarction, hematoma volume, and loss of neuronal activity. RNF34 and oxidative stress levels gradually increased from 6 to 48 h after the ICH challenge and were positively correlated. The ICH-induced increase in intracellular ROS, superoxide anion, and mROS generation and the decrease in adenosine triphosphate production were exacerbated in RNF34 transgenic mice, but NADPH oxidase activity was unaffected. Moreover, RNF34 upregulation potentiated the ICH-induced decrease in PGC-1α, UCP2, and MnSOD expressions. RNF34 interacted with PGC-1α and targeted it for ubiquitin-dependent degradation. This study reveals that RNF34 exacerbates neurological deficits and brain injury by facilitating PGC-1α protein degradation and promoting mitochondrial dysfunction-mediated oxidative stress.

Sodium butyrate-activated TRAF6-TXNIP pathway affects A549 cells proliferation and migration

TNF receptor‐associated factor 6 (TRAF6) promotes the development of human lung cancer through bridging RAS and NF‐kB pathways; on the other hand, thioredoxin‐interacting protein (TXNIP) suppresses the growth of tumors. However, the crosstalk between TRAF6 and TXNIP in non‐small cell lung cancer (NSCLC) is currently unclear. Here, we found that TXNIP expression induced by sodium butyrate (NaBu) was TRAF6‐dependent. Moreover, TXNIP interacted with TRAF6 via its PPxY motif. Polyubiquitylation analysis with wild‐type or mutant (Cysteine70 to Alanine) of TRAF6 further showed TRAF6 ubiquitylated TXNIP. NaBu reinforced the interaction of TRAF6/TXNIP as well as TXNIP’ polyubiquitylation. Moreover, treated with NaBu, the A549 cells with TRAF6/TXNIP double knockdown showed an enhanced protein expression of E‐cadherin comparing to cells with single gene or negative knockdown. The experimental results of transwell and nude mice xenograft showed that knocking down both TRAF6 and TXNIP in A549 cells affected its migration and proliferation compared to that of single knockdown or negative control cells. On the other hand, TXNIP localization was different depending on the cell types and fused‐tag (eg, FLAG or GFP). Our results revealed TRAF6 regulated the expression and polyubiquitylation of TXNIP in a NaBu‐dependent manner, alleviating tumorigenesis of TRAF6.

PRDX1 enhances cerebral ischemia-reperfusion injury through activation of TLR4-regulated inflammation and apoptosis

Stroke is still a leading cause of death across the world. Despite various signals or molecules that contribute to the pathophysiological process have been investigated, the exact molecular mechanisms revealing stroke damage still remain to be explored. Peroxiredoxin 1 (PRDX1) has been identified as a stress-induced macrophage redox protein with multiple functions. Although PRDX1 is a critical factor related to the regulation of immunity, inflammation, apoptosis and oxidative stress, its effects on cerebral ischemia-reperfusion (I-R) injury were presently unclear. In the study, by using a mouse model of I-R injury, we found that PRDX1 expression was up-regulated during I-R injury in a time-dependent manner. Additionally, PRDX1-knockout mice showed reduced infarction area and alleviated neuropathological scores with decreased brain water contents. Furthermore, cell death and inflammatory response in mice with cerebral I-R injury were markedly attenuated by PRDX1 knockout, which were associated with the blockage of Caspase-3 and nuclear factor-κB (NF-κB) signaling pathways. Mechanistically, PRDX1-regulated cerebral I-R injury was through the promotion of toll-like receptor-4 (TLR4), as proved by the evidence that TLR4 suppression abrogated the exacerbated effect of TLR4 on inflammatory response and apoptosis in oxygen and glucose deprivation (OGD)-treated primary microglial cells. These data demonstrated that PRDX1 contributed to cerebral stroke by interacting with TLR4, providing an effective therapeutic approach for cerebral I-R injury.

Ubiquitin-based modifications in endothelial cell-cell contact and inflammation

Endothelial cell-cell contacts are essential for vascular integrity and physiology, protecting tissues and organs from edema and uncontrolled invasion of inflammatory cells. The vascular endothelial barrier is dynamic, but its integrity is preserved through a tight control at different levels. Inflammatory cytokines and G-protein-coupled receptor agonists, such as histamine, reduce endothelial integrity and increase vascular leakage. This is due to elevated myosin-based contractility, in conjunction with phosphorylation of proteins at cell-cell contacts. Conversely, reducing contractility stabilizes or even increases endothelial junctional integrity. Rho GTPases are key regulators of such cytoskeletal dynamics and endothelial cell-cell contacts. In addition to signaling-induced regulation, the expression of junctional proteins, such as occludin, claudins and vascular endothelial cadherin, also controls endothelial barrier function. There is increasing evidence that, in addition to protein phosphorylation, ubiquitylation (also known as ubiquitination) is an important and dynamic post-translational modification that regulates Rho GTPases, junctional proteins and, consequently, endothelial barrier function. In this Review, we discuss the emerging role of ubiquitylation and deubiquitylation events in endothelial integrity and inflammation. The picture that emerges is one of increasing complexity, which is both fascinating and promising given the clinical relevance of vascular integrity in the control of inflammation, and of tissue and organ damage.

Site-specific phosphorylation of Fbxw7 by Cdk5/p25 and its resulting decreased stability are linked to glutamate-induced excitotoxicity

Cyclin-dependent kinase 5 (Cdk5) is a serine/threonine protein kinase that regulates brain development and neurodegeneration. Cdk5 is activated by p25 that is generated from calpain-dependent cleavage of p35. The generation of p25 is responsible for the aberrant hyper-activation of Cdk5, which causes neurodegeneration. Using in vitro assays, we discovered that F-box/WD repeat-containing protein 7 (Fbxw7) is a new substrate of Cdk5. Additionally, Cdk5-dependent phosphorylation of Fbxw7 was detected in the presence of p25, and two amino acid residues (S349 and S372) were determined to be major phosphorylation sites. This phosphorylation was eventually linked to decreased stability of Fbxw7. Using a culture model of cortical neurons challenged with glutamate, we confirmed that decreased stability of Fbxw7 was indeed Cdk5-dependent. Furthermore, diminished levels of Fbxw7 led to increased levels of transcription factor AP-1 (c-Jun), a known substrate of Fbxw7. Given that previous reports demonstrate that c-Jun plays a role in accelerating neuronal apoptosis in these pathological models, our data support the concepts of a molecular cascade in which Cdk5-mediated phosphorylation of Fbxw7 negatively regulates Fbxw7 expression, thereby contributing to neuronal cell death following glutamate-mediated excitotoxicity.

Silencing of Long Noncoding RNA Nespas Aggravates Microglial Cell Death and Neuroinflammation in Ischemic Stroke

Background and Purpose- Ischemic stroke is one of the leading causes of morbidity and mortality worldwide and a major cause of long-term disability. Recently, long noncoding RNAs have been revealed, which are tightly associated with several human diseases. However, the functions of long noncoding RNAs in ischemic stroke still remain largely unknown. In the current study, for the first time, we investigated the role of long noncoding RNA Nespas in ischemic stroke. Methods- We used in vivo models of middle cerebral artery occlusion and in vitro models of oxygen-glucose deprivation to illustrate the effect of long noncoding RNA Nespas on ischemic stroke. Results- We found expression of Nespas was significantly increased in ischemic cerebral tissues and oxygen-glucose deprivation-treated BV2 cells in a time-dependent manner. Silencing of Nespas aggravated middle cerebral artery occlusion operation-induced IR injury and cell death. In addition, proinflammatory cytokine production and NF-κB (nuclear factor-κB) signaling activation were inhibited by Nespas overexpression. TAK1 (transforming growth factor-β-activated kinase 1) was found to directly interact with Nespas, and TAK1 activation was significantly suppressed by Nespas. At last, we found Nespas-inhibited TRIM8 (tripartite motif 8)-induced K63-linked polyubiquitination of TAK1. Conclusions- We showed that Nespas played anti-inflammatory and antiapoptotic roles in cultured microglial cells after oxygen-glucose deprivation stimulation and in mice after ischemic stroke by inhibiting TRIM8-related K63-linked polyubiquitination of TAK1.

CSN5 inhibition triggers inflammatory signaling and Rho/ROCK-dependent loss of endothelial integrity

RhoGTPases regulate cytoskeletal dynamics, migration and cell-cell adhesion in endothelial cells. Besides regulation at the level of guanine nucleotide binding, they also undergo post-translational modifications, for example ubiquitination. RhoGTPases are ubiquitinated by Cullin RING ligases which are in turn regulated by neddylation. Previously we showed that inhibition of Cullin RING ligase activity by the neddylation inhibitor MLN4924 is detrimental for endothelial barrier function, due to accumulation of RhoB and the consequent induction of contractility. Here we analyzed the effect of pharmacological activation of Cullin RING ligases on endothelial barrier integrity in vitro and in vivo. CSN5i-3 induced endothelial barrier disruption and increased macromolecule leakage in vitro and in vivo. Mechanistically, CSN5i-3 strongly induced the expression and activation of RhoB and to lesser extent of RhoA in endothelial cells, which enhanced cell contraction. Elevated expression of RhoGTPases was a consequence of activation of the NF-κB pathway. In line with this notion, CSN5i-3 treatment decreased IκBα expression and increased NF-κB-mediated ICAM-1 expression and consequent adhesion of neutrophils to endothelial cells. This study shows that sustained neddylation of Cullin RING-ligases leads to activation the NF-κB pathway in endothelial cells, elevated expression of RhoGTPases, Rho/ROCK-dependent activation of MLC and disruption of the endothelial barrier.

Control of mTOR signaling by ubiquitin

The evolutionarily conserved mTOR signaling pathway plays essential roles in cell growth, proliferation, metabolism and responses to cellular stresses. Hyperactivation of the mTOR signaling is observed in virtually all solid tumors and has been an attractive drug target. In addition to changes at genetic levels, aberrant activation of the mTOR signaling is also a result from dysregulated post-translational modifications on key pathway members, such as phosphorylation that has been extensively studied. Emerging evidence also support a critical role for ubiquitin-mediated modifications in dynamically regulating the mTOR signaling pathway, while a comprehensive review for relevant studies is missing. In this review, we will summarize all characterized ubiquitination events on major mTOR signaling components, their modifying E3 ubiquitin ligases, deubiquitinases and corresponding pathophysiological functions. We will also reveal methodologies that have been used to identify E3 ligases or DUBs to facilitate the search for yet-to-be discovered ubiquitin-mediated regulatory mechanisms in mTOR signaling. We hope that our review and perspectives provide rationales and strategies to target ubiquitination for inhibiting mTOR signaling to treat human diseases.

Retracted Article: Elevation of USP4 antagonizes oxygen glucose deprivation/reoxygenation-evoked microglia activation and neuroinflammation-mediated neurotoxicity via the TRAF6-NF-κB signaling

An ischemic stroke is a devastating neurological disease with the typical occurrence of brain ischemia/reperfusion (I/R) injury, and it has high mortality and disability globally. Microglia activation after a stroke results in the release of pro-inflammatory cytokines that can further aggravate brain damage. A recent study confirmed the potential role of ubiquitin-specific peptidase 4 (USP4) in the injury process. Nevertheless, the role and mechanism of USP4 during an ischemic stroke remain elusive. In this research, we simulated an I/R injury by oxygen glucose deprivation/reoxygenation (OGD/R) in vitro and confirmed the obvious down-regulation of USP4 in microglia under OGD/R conditions. Moreover, USP4 elevation antagonized the OGD/R-induced microglia proliferation and activation by suppressing the NO levels and the expression of the microglial marker IBA-1. Additionally, the overexpression of USP4 suppressed the release of microglia activation-induced pro-inflammatory cytokines, including IL-1β, IL-6, and TNF-α. Intriguingly, incubation with the conditioned medium from the microglia under OGD/R conditions induced neurotoxicity by inhibiting cell viability and increasing the LDH release, apoptosis, and caspase-3 activity, which were reversed following USP4 overexpression. Mechanism analysis corroborated that USP4 up-regulation repressed the OGD/R-induced activation of TRAF6-NF-κB signaling. Notably, restoring the TRAF6 signaling ameliorated the suppressive effects of USP4 elevation on microglia activation, inflammation, and the subsequent neuron injury. These findings suggest that USP4 may alleviate ischemic stroke by restraining microglia-mediated neuro-inflammation and neurotoxicity via the TRAF6-NF-κB pathway, due to which it is a promising therapeutic agent against strokes.

An ischemic stroke is a devastating neurological disease with the typical occurrence of brain ischemia/reperfusion (I/R) injury, and it has high mortality and disability globally.

Degradation of TRPML1 in Neurons Reduces Neuron Survival in Transient Global Cerebral Ischemia

Postcardiac arrest syndrome yields poor neurological outcomes, but the mechanisms underlying this condition remain poorly understood. Autophagy plays an important role in neuronal apoptosis induced by ischemia. However, whether autophagy is involved in neuron apoptosis induced by cardiac arrest has been less studied. This study found that TRPML1 participates in cerebral ischemic reperfusion injury. Primary neurons were isolated and treated with mucolipin synthetic agonist 1 (ML-SA1), as well as infected with the recombinant lentivirus TRPML1 overexpression vector in vitro. ML-SA1 was delivered intracerebroventricularly in transient global ischemia model. Protein expression levels were determined by western blot. Neurological deficit score and the infarct volume were analyzed for the detection of neuronal damage. We found that TRPML1 was significantly downregulated in vivo and in vitro ischemic reperfusion model. We also observed that TRPML1 overexpression or treatment with the ML-SA1 attenuated neuronal death in primary neurons and ameliorated neurological dysfunction in vivo. Our findings suggested that autophagy and apoptosis were activated after transient global ischemia. Administration of ML-SA1 before transient global ischemia ameliorated neurological dysfunction possibly through the promotion of autophagy and the inhibition of apoptosis.

Role of Innate Immune Signaling in Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) has become the most epidemic liver disease worldwide owing to rapid changes in lifestyle over the past few decades. This chronic condition intertwines with low-grade inflammation and metabolic disequilibrium, and potentiates the onset and progression of devastating hepatic and extrahepatic complications. In addition to an integral role in promoting host defense, recent studies also implicate innate immune signaling in a multitude of processes that control the progression of NAFLD. The focus of this review is to highlight emerging evidence regarding the role of innate immunity in NAFLD and the integration of different pathways that affect both inflammation and metabolism across the spectrum of this liver morbidity.