TRADD mediates the tumor necrosis factor-induced apoptosis of L929 cells in the absence of RIP3

Hydrogen sulfide plays an important role by regulating microRNA in different ischemia-reperfusion injury

MicroRNAs (miRNAs) are the short endogenous non-coding RNAs that regulate the expression of the target gene at posttranscriptional level through degrading or inhibiting the specific target messenger RNAs (mRNAs). MiRNAs regulate the expression of approximately one-third of protein coding genes, and in most cases inhibit gene expression. MiRNAs have been reported to regulate various biological processes, such as cell proliferation, apoptosis and differentiation. Therefore, miRNAs participate in multiple diseases, including ischemia-reperfusion (I/R) injury. Hydrogen sulfide (H2S) was once considered as a colorless, toxic and harmful gas with foul smelling. However, in recent years, it has been discovered that it is the third gas signaling molecule after carbon monoxide (CO) and nitric oxide (NO), with multiple important biological functions. Increasing evidence indicates that H2S plays a vital role in I/R injury through regulating miRNA, however, the mechanism has not been fully understood. In this review, we summarized the current knowledge about the role of H2S in I/R injury by regulating miRNAs, and analyzed its mechanism in detail.

Contents of exosomes derived from adipose tissue and their regulation on inflammation, tumors, and diabetes

Adipose tissue (AT) serves as an energy-capacitive organ and performs functions involving paracrine- and endocrine-mediated regulation via extracellular vesicles (EVs) secretion. Exosomes, a subtype of EVs, contain various bioactive molecules with regulatory effects, such as nucleic acids, proteins, and lipids. AT-derived exosomes (AT-exos) include exosomes derived from various cells in AT, including adipocytes, adipose-derived stem cells (ADSCs), macrophages, and endothelial cells. This review aimed to comprehensively evaluate the impacts of different AT-exos on the regulation of physiological and pathological processes. The contents and functions of adipocyte-derived exosomes and ADSC-derived exosomes are compared simultaneously, highlighting their similarities and differences. The contents of AT-exos have been shown to exert complex regulatory effects on local inflammation, tumor dynamics, and insulin resistance. Significantly, differences in the cargoes of AT-exos have been observed among diabetes patients, obese individuals, and healthy individuals. These differences could be used to predict the development of diabetes mellitus and as therapeutic targets for improving insulin sensitivity and glucose tolerance. However, further research is needed to elucidate the underlying mechanisms and potential applications of AT-exos.

Effect of S-Nitrosylation of RIP3 Induced by Cerebral Ischemia on its Downstream Signaling Pathway

OBJECTIVES

Our preliminary experiments indicate that receptor-interacting protein 3 (RIP3) is S-nitrosylated and contributes to its autophosphorylation (activation) after 3 h of rat brain ischemia/reperfusion mediated by activation of the N-methyl-D-aspartate receptor (NMDAR)-dependent neuronal NO synthase (nNOS) and is involved in the process of neuronal injury. Here, we will to demonstrate whether S-nitrosylation of RIP3 facilitates the activation of the downstream signaling pathway and finally exacerbates ischemic neuron death.

MATERIALS AND METHODS

Adult male Sprague-Dawley rat transient brain ischemia/reperfusion and cortical neurons oxygen and glucose deprivation (OGD)/reoxygenation models were performed. The hippocampal CA1 regions or cultured cells were homogenized and the cytosolic fraction were collected as tissue samples. Coimmunoprecipitation and western blot analysis were carried out for detecting phosphorylation of RIP1 and mixed lineage kinase-like domains (MLKL) and the Cleaved-Caspase8 (Cl-Caspase8). The activities of Glycogen phosphorylase (PYGL), Glutamate-ammonia ligase (GLUL) and Glutamate dehydrogenase (GLUD1) were detected with ultraviolet absorption method.

RESULTS

This study showed that active RIP3 could phosphorylate RIP1 and MLKL through its kinase activity, promote the conversion of Caspase8 to active Cl-Caspase8, enhance the activities of PYGL, GLUL and GLUD1, and finally aggravate neuronal injury in cerebral ischemia/reperfusion. The inhibition of RIP3 S-nitrosylation inhibited the phosphorylation of RIP1 and MLKL, inhibited the activities of Caspase8, PYGL, GLUL, and GLUD1, and alleviated neuronal damage in cerebral ischemia/reperfusion.

CONCLUSIONS

S-nitrosylation of RIP3 increased RIP1 and MLKL phosphorylation levels, Cl-Caspase8 content and PYGL, GLUL and GLUD1 activities and aggravated neuronal damage during cerebral ischemia/reperfusion and regulating the S-nitrosylation of RIP3 and its downstream signaling pathway might be a therapeutic target for stroke.

Early onset senescence and cognitive impairment in a murine model of repeated mTBI

Mild traumatic brain injury (mTBI) results in broad neurological symptoms and an increased risk of being diagnosed with a neurodegenerative disease later in life. While the immediate oxidative stress response and post-mortem pathology of the injured brain has been well studied, it remains unclear how early pathogenic changes may drive persistent symptoms and confer susceptibility to neurodegeneration. In this study we have used a mouse model of repeated mTBI (rmTBI) to identify early gene expression changes at 24 h or 7 days post-injury (7 dpi). At 24 h post-injury, gene expression of rmTBI mice shows activation of the DNA damage response (DDR) towards double strand DNA breaks, altered calcium and cell–cell signalling, and inhibition of cell death pathways. By 7 dpi, rmTBI mice had a gene expression signature consistent with induction of cellular senescence, activation of neurodegenerative processes, and inhibition of the DDR. At both timepoints gliosis, microgliosis, and axonal damage were evident in the absence of any gross lesion, and by 7 dpi rmTBI also mice had elevated levels of IL1β, p21, 53BP1, DNA2, and p53, supportive of DNA damage-induced cellular senescence. These gene expression changes reflect establishment of processes usually linked to brain aging and suggests that cellular senescence occurs early and most likely prior to the accumulation of toxic proteins. These molecular changes were accompanied by spatial learning and memory deficits in the Morris water maze. To conclude, we have identified DNA damage-induced cellular senescence as a repercussion of repeated mild traumatic brain injury which correlates with cognitive impairment. Pathways involved in senescence may represent viable treatment targets of post-concussive syndrome. Senescence has been proposed to promote neurodegeneration and appears as an effective target to prevent long-term complications of mTBI, such as chronic traumatic encephalopathy and other related neurodegenerative pathologies.

Loss of FADD and Caspases Affects the Response of T-Cell Leukemia Jurkat Cells to Anti-Cancer Drugs

Programmed cell death (PCD) pathways play a crucial role in the response of cancer cells to treatment. Their dysregulation is one of the cancer hallmarks and one of the reasons of drug resistance. Here, we studied the significance of the individual members of PCD signaling pathways in response to treatment with common anti-cancer drugs using the T-cell leukemia Jurkat cells with single or double knockouts of necroptosis and/or apoptosis genes. We identified apoptosis as the primary cell death pathway upon anti-cancer drugs treatment. The cells with knocked out either Fas-associated protein with death domain (FADD) or all executioner caspases were resistant. This resistance could be partially overcome by induction of RIP1-dependent necroptosis through TNFR1 activation using combined treatment with TNF-α and smac mimetic (LCL161). RIP1 was essential for cellular response to TNF-α and smac mimetic, but dispensable for the response to anti-cancer drugs. Here, we demonstrated the significance of FADD and executioner caspases in carrying out programmed cell death upon anti-cancer drug treatments and the ability of combined treatment with TNF-α and smac mimetic to partially overcome drug resistance of FADD and/or CASP3/7/6-deficient cells via RIP1-dependent necroptosis. Thus, a combination of TNF-α and smac mimetic could be a suitable strategy for overcoming resistance to therapy in cells unable to trigger apoptosis.

Analysis of long-term results of pathogenetic treatment of Helicobacter pylori-associated gastroduodenopathies induced by nonsteroidal anti-inflammatory drugs in patients with osteoarthritis

The study of the pathogenetic treatment and prevention of Helicobacter pylori (Hp)-associated gastroduodenopathies (GDP) induced by nonsteroidal anti-inflammatory drugs (NSAIDs) in patients with osteoarthritis (OA) is one of the most serious problems in modern clinical medicine. Sixty patients with OA and concomitant Hp-associated GDP induced by NSAIDs were examined. The levels of epidermal growth factor (EDF), sAPO-1/Fas and tumor necrosis factor-α (TNF-α) were determined. Group I included 30 patients who received triple anti-Helicobacter (AHT) therapy, and group II included 30 patients who received rebamipide. Long-term effects were assessed 6 months and 1 year after treatment. All subjects showed a significant increase in TNF-α (4.7 times), EDF (2.2 times) and a decrease in sAPO-1/Fas (3.6 times) levels compared to healthy individuals. After 1 month of treatment, a significantly more significant decrease in TNF-α and an increase in sAPO-1/Fas and EDF was found in group II. In the long-term treatment, a further decrease in TNF-α and an increase in the content of sAPO-1/Fas levels were observed in all groups. However, these changes were significantly more significant in group I compared to group I. The long-term follow-up showed a declining trend of EDF in all groups. The data obtained indicate the effectiveness of rebamipide in the complex pathogenetic treatment and prevention of Hp-associated GDP induced by NSAIDs in patients with OA.

PI3K mediates tumor necrosis factor induced-necroptosis through initiating RIP1-RIP3-MLKL signaling pathway activation

Necroptosis is a recently identified programmed cell death, which is initiated by receptor-interacting serine/threonine-protein kinase 1 (RIP1), RIP3 and mixed-lineage kinase domain-like protein (MLKL). It has been reported that necroptosis induced by tumor necrosis factor (TNF) was inhibited by the inhibitor of phosphatidylinositol-3-kinase (PI3K) and its substrate protein AKT, indicating that PI3K-AKT signaling pathway was involved in mediating TNF-induced necroptosis, whereas it is unclear how PI3K initiates necroptosis. In this study, we found that TNF-induced necroptosis was inhibited by chemical inhibition or genetic deletion of PI3K. Moreover, knockdown of p110α, the catalytic subunit of PI3K, significantly suppressed the phosphorylation of PI3K substrate protein AKT, and TNF-induced necroptosis was blocked by AKT inhibitors. Furthermore, we found that p110α knockdown also suppressed the phosphorylation and oligomerization of RIP1, RIP3 and MLKL in response to TNF stimulation. In addition to the critical role in mediating TNF-induced necrosome formation, p110α was also essential for the spontaneous phosphorylation of RIP1 and RIP3. Finally, we found that p110α bound to RIP3, but not RIP1, to form protein complex in the process of TNF-induced necroptosis, and mediated TNF-induced necroptosis in the absence of RIP1. Our results demonstrate that PI3K is essential for TNF-induced necroptosis, which may act as the partner of RIP3 to initiate the activation of RIP1-RIP3-MLKL signal pathway and the subsequent necroptosis.

SNHG9, delivered by adipocyte-derived exosomes, alleviates inflammation and apoptosis of endothelial cells through suppressing TRADD expression

Exosomes are membrane-derived vesicles and play a critical role in cell signaling by transferring RNAs and proteins to target cells through fusion with the cell membrane. Long non-coding RNA-small nucleolar RNA host gene 9 (lncRNA-SNHG9) was proven to be an important element in lncRNA-mRNA interaction networks during adipocyte differentiation, suggesting its potential involvement in the development of obesity, an important risk factor of cardiovascular and cerebrovascular endothelial dysfunction. However, the role of lncRNA-SNHG9 within the exosome in endothelial dysfunction of obese patients is largely unknown. In this study, we proved that adipocytes-derived exosomal SNHG9 were downregulated in obese persons and further decreased in obese individuals with endothelial dysfunction. Functional experimentations demonstrated that adipocytes-derived exosomal SNHG9 alleviated inflammation and apoptosis in endothelial cells. Bioinformatic analysis revealed that there was a potential interaction between SNHG9 and the TNF receptor type 1-associated death domain protein (TRADD) mRNA. Then, RNA-binding protein immunoprecipitation assay based on Ago2 antibody and ribonuclease protection assay demonstrated that exosomal SNHG9 directly bound to a specific region in TRADD mRNA sequence and formed an RNA dimeric inducible silencing complex. Moreover, knockdown of TRADD markedly inhibited inflammation and apoptosis in human umbilical vein endothelial cells (HUVECs), whereas overexpression of TRADD dramatically neutralized the protective effect of exosomal SNHG9 on epithelial dysfunction. Therefore, SNHG9 could prevent endothelial dysfunction in obese patients by suppressing inflammation and apoptosis, indicating that SNHG9 may be a potential therapeutic target for obese patients with endothelial dysfunction.

TRADD Mediates RIPK1-Independent Necroptosis Induced by Tumor Necrosis Factor

As a programmed necrotic cell death, necroptosis has the intrinsic initiators, including receptor-interacting serine/threonine-protein kinase 1 (RIPK1), RIPK3 and mixed-lineage kinase domain-like protein (MLKL), which combine to form necroptotic signaling pathway and mediate necroptosis induced by various necroptotic stimuli, such as tumor necrosis factor (TNF). Although chemical inhibition of RIPK1 blocks TNF-induced necroptosis, genetic elimination of RIPK1 does not suppress but facilitate necroptosis triggered by TNF. Moreover, RIPK3 has been reported to mediate the RIPK1-independent necroptosis, but the involved mechanism is unclear. In this study, we found that TRADD was essential for TNF-induced necroptosis in RIPK1-knockdown L929 and HT-22 cells. Mechanistic study demonstrated that TRADD bound RIPK3 to form new protein complex, which then promoted RIPK3 phosphorylation via facilitating RIPK3 oligomerization, leading to RIPK3-MLKL signaling pathway activation. Therefore, TRADD acted as a partner of RIPK3 to initiate necroptosis in RIPK1-knockdown L929 and HT-22 cells in response to TNF stimulation. In addition, TRADD was critical for the accumulation of reactive oxygen species (ROS), which contributed to RIPK1-independent necroptosis triggered by TNF. Collectively, our data demonstrate that TRADD acts as the new target protein for TNF-induced RIPK3 activation and the subsequent necroptosis in a RIPK1-independent manner.

miR-149-5p mitigates tumor necrosis factor-α-induced chondrocyte apoptosis by inhibiting TRADD

Introduction

Chondrocyte apoptosis as a prominent characteristic is usually accompanied by cartilage degeneration in osteoarthritis (OA). Herein, we aimed to determine the roles of miR-149-5p in tumor necrosis factor-α (TNF-α)-induced chondrocyte apoptosis.

Material and methods

Human chondrocytes were cultured with TNF-α to establish an apoptosis cell model in vitro. After transfection with miR-149-5p mimics or co-expression with TRADD in chondrocytes, cell viability, apoptosis, inflammatory cytokines, mRNA and protein expression were measured using CCK8, Annexin V-FITC double staining, ELISA assays, RT-qPCR and western blotting, respectively.

Results

TNF-α-induced chondrocyte apoptosis occurred in association with the inhibition of cell proliferation, the elevation of inflammatory cytokine levels and the activation of TRADD and caspase-3/8 signaling. The post-transcriptional regulatory mechanism suggested that TRADD was a direct target of miR-149-5p, and overexpression of miR-149-5p resulted in the down-regulation of TRADD protein expression in chondrocytes. In addition, miR-149-5p mimics had the ability to attenuate TNF-α-induced inflammation and apoptosis, while transfection with TRADD vector neutralized the protective effects of miR-149-5p on TNF-α-induced chondrocyte dysfunction.

Conclusions

miR-149-5p inversely regulated TNF-α-mediated chondrocyte damage by inhibiting TRADD-modulated caspases signaling. The miR-149-5p/TRADD signaling pathway might be a promising therapeutic target for the treatment of OA.

Death domain of p75 neurotrophin receptor: a structural perspective on an intracellular signalling hub

The death domain (DD) is a globular protein motif with a signature feature of an all-helical Greek-key motif. It is a primary mediator of a variety of biological activities, including apoptosis, cell survival and cytoskeletal changes, which are related to many neurodegenerative diseases, neurotrauma, and cancers. DDs exist in a wide range of signalling proteins including p75 neurotrophin receptor (p75^NTR ), a member of the tumour necrosis factor receptor superfamily. The specific signalling mediated by p75^NTR in a given cell depends on the type of ligand engaging the extracellular domain and the recruitment of cytosolic interactors to the intracellular domain, especially the DD, of the receptor. In solution, the p75^NTR -DDs mainly form a symmetric non-covalent homodimer. In response to extracellular signals, conformational changes in the p75^NTR extracellular domain (ECD) propagate to the p75^NTR -DD through the disulfide-bonded transmembrane domain (TMD) and destabilize the p75^NTR -DD homodimer, leading to protomer separation and exposure of binding sites on the DD surface. In this review, we focus on recent advances in the study of the structural mechanism of p75^NTR -DD signalling through recruitment of diverse intracellular interactors for the regulation and control of diverse functional outputs.