Nutrient deprivation induces apoptosis of nucleus pulposus cells via activation of the BNIP3/AIF signalling pathway

Targeting nucleus pulposus cell death in the treatment of intervertebral disc degeneration

Background

Intervertebral disc degeneration (IDD) is a progressive age-related disorder characterized by the reduction in the number of nucleus pulposus cells (NPCs) and degradation of extracellular matrix (ECM), thereby leading to chronic pain and disability. The pathogenesis of IDD is multifaceted, and current therapeutic strategies remain limited. The nucleus pulposus (NP), primarily composed of NPCs, proteoglycans, and type II collagen, constitutes essential components for maintaining intervertebral disc (IVD) function and spinal motion. The disturbed homeostasis of NPCs is closely associated with IDD. Accumulating evidence increasingly suggests the crucial role of programmed cell death (PCD) in regulating the homeostasis of NPCs.

Aims

This review aimed to elucidate various forms of PCD and their respective roles in IDD, and investigate diverse strategies targeting the cell death of NPCs for IDD treatment.

Materials & Methods

We collected the relevant literature regarding PCD and their roles in the development of IDD. Subsequently, we comprehensively summarized the intricate association between PCD and IDD, and also explored the potential and application of cell therapy and traditional Chinese medicine (TCM) in the prevention and treatment of IDD.

Results

Current literature indicated that the PCD of NPCs was closely associated with the pathogenesis of IDD. Additionally, the development of targeted pharmaceuticals based on the mechanisms of PCD could effectively impede the loss of NPCs.

Conclusion

This review demonstrated that targeting the PCD of NPCs may be a promising strategy for the treatment of IDD.

Glucose depletion decreases cell viability without triggering degenerative changes in a physiological nucleus pulposus explant model

Although the etiology of intervertebral disc degeneration is still unresolved, the nutrient paucity resulting from its avascular nature is suspected of triggering degenerative processes in its core: the nucleus pulposus (NP). While severe hypoxia has no significant effects on NP cells, the impact of glucose depletion, such as found in degenerated discs (0.2-1 mM), is still uncertain. Using a pertinent ex-vivo model representative of the unique disc microenvironment, the present study aimed, therefore, at determining the effects of "degenerated" (0.3 mM) glucose levels on bovine NP explant homeostasis. The effects of glucose depletion were evaluated on NP cell viability, apoptosis, phenotype, metabolism, senescence, extracellular matrix anabolism and catabolism, and inflammatory mediator production using fluorescent staining, RT-qPCR, (immuno)histology, ELISA, biochemical, and enzymatic assays. Compared to the "healthy" (2 mM) glucose condition, exposure to the degenerated glucose condition led to a rapid and extensive decrease in NP cell viability associated with increased apoptosis. Although the aggrecan and collagen-II gene expression was also downregulated, NP cell phenotype, and senescence, matrix catabolism, and inflammatory mediator production were not, or only slightly, affected by glucose depletion. The present study provided evidence for glucose depletion as an essential player in NP cell viability but also suggested that other microenvironment factor(s) may be involved in triggering the typical shift of NP cell phenotype observed during disc degeneration. The present study contributes new information for better understanding disc degeneration at the cellular-molecular levels and thus helps to develop relevant therapeutical strategies to counteract it.

M6A methylation-regulated autophagy may be a new therapeutic target for intervertebral disc degeneration

Degeneration of intervertebral discs is considered one of the most important causes of low back pain and disability. The intervertebral disc (IVD) is characterized by its susceptibility to various stressors that accelerate the senescence and apoptosis of nucleus pulposus cells, resulting in the loss of these cells and dysfunction of the intervertebral disc. Therefore, how to reduce the loss of nucleus pulposus cells under stress environment is the main problem in treating intervertebral disc degeneration. Autophagy is a kind of programmed cell death, which can provide energy by recycling substances in cells. It is considered to be an effective method to reduce the senescence and apoptosis of nucleus pulposus cells under stress. However, further research is needed on the mechanisms by which autophagy of nucleus pulposus cells is regulated under stress environments. M6A methylation, as the most extensive RNA modification in eukaryotic cells, participates in various cellular biological functions and is believed to be related to the regulation of autophagy under stress environments, may play a significant role in nucleus pulposus responding to stress. This article first summarizes the effects of various stressors on the death and autophagy of nucleus pulposus cells. Then, it summarizes the regulatory mechanism of m6A methylation on autophagy-related genes under stress and the role of these autophagy genes in nucleus pulposus cells. Finally, it proposes that the methylation modification of autophagy-related genes regulated by m6A may become a new treatment approach for intervertebral disc degeneration, providing new insights and ideas for the clinical treatment of intervertebral disc degeneration.

Comparative Analysis of Autophagy and Apoptosis in Disc Degeneration: Understanding the Dynamics of Temporary-Compression-Induced Early Autophagy and Sustained-Compression-Triggered Apoptosis

The purpose of this study was to investigate the initiation of autophagy activation and apoptosis in nucleus pulposus cells under temporary compression (TC) and sustained compression (SC) to identify ideal research approaches in intervertebral disc degeneration. Various techniques were used: radiography (X-ray), magnetic resonance imaging (MRI), transmission electron microscope (TEM), H&E staining, Masson's trichrome staining, immunohistochemistry (IHC) (LC3, beclin-1, and cleaved caspase-3), and real-time polymerase chain reaction (RT-qPCR) for autophagy-related (beclin-1, LC3, and P62) and apoptosis-related (caspase-3 and PARP) gene expression analysis. X-ray and MRI revealed varying degrees of disc degeneration, ranging from moderate to severe in both groups. The severity was directly linked to compression duration, with SC resulting in notably severe central NP cell degeneration. Surprisingly, TC also caused similar, though less severe, degeneration. Elevated expression of LC3 and beclin-1 was identified after 6 weeks, but it notably declined after 12 weeks. Central NP cells in both groups exhibited increased expression of cleaved caspase-3 that was positively correlated with the duration of SC. TC showed fewer apoptotic markers compared to SC. LC3, beclin-1, and P62 mRNA expression peaked after 6 weeks and declined after 12 weeks in both groups. Cleaved caspase-3 and PARP expression peaked in SC, positively correlating with longer compression duration, while TC showed lower levels of apoptosis gene expression. Furthermore, TEM results revealed different events of the autophagic degradation process after 2 weeks of compression. TCmay be ideal for studying early triggered autophagy-mediated degeneration, while SC may be ideal for studying late or slower-triggered apoptosis-mediated degeneration.

The Duration of Oxygen and Glucose Deprivation (OGD) Determines the Effects of Subsequent Reperfusion on Rat Pheochromocytoma (PC12) Cells and Primary Cortical Neurons

Reperfusion is the fundamental treatment for ischaemic stroke; however, many ischaemic stroke patients cannot undergo reperfusion treatment. Furthermore, reperfusion can cause ischaemic reperfusion injuries. This study aimed to determine the effects of reperfusion in an in vitro ischaemic stroke model-oxygen and glucose deprivation (OGD) (0.3% O2)-with rat pheochromocytoma (PC12) cells and cortical neurons. In PC12 cells, OGD resulted in a time-dependent increase in cytotoxicity and apoptosis, and reduction in MTT activity from 2 h onwards. Reperfusion following shorter periods (4 and 6 h) of OGD recovered apoptotic PC12 cells, whereas after 12 h, OGD increased LDH release. In primary neurons, 6 h OGD led to significant increase in cytotoxicity, reduction in MTT activity and dendritic MAP2 staining. Reperfusion following 6 h OGD increased the cytotoxicity. HIF-1a was stabilised by 4 and 6 h OGD in PC12 cells and 2 h OGD onwards in primary neurons. A panel of hypoxic genes were upregulated by the OGD treatments depending on the duration. In conclusion, the duration of OGD determines the mitochondrial activity, cell viability, HIF-1a stabilization, and hypoxic gene expression in both cell types. Reperfusion following OGD of short duration is neuroprotective, whereas OGD of long duration is cytotoxic.

Quiescence preconditioned nucleus pulposus stem cells alleviate intervertebral disc degeneration by enhancing cell survival via adaptive metabolism pattern in rats

Quiescence is a cellular state of reversible growth arrest required to maintain homeostasis and self-renewal. Entering quiescence allows the cells to remain in the non-dividing stage for an extended period of time and enact mechanisms to protect themselves from damage. Due to the extreme nutrient-deficient microenvironment in the intervertebral disc (IVD), the therapeutic effect of cell transplantation is limited. In this study, nucleus pulposus stem cells (NPSCs) were preconditioned into quiescence through serum starvation in vitro and transplanted to repair intervertebral disc degeneration (IDD). In vitro, we investigated apoptosis and survival of quiescent NPSCs in a glucose-free medium without fetal bovine serum. Non-preconditioned proliferating NPSCs served as controls. In vivo, the cells were transplanted into a rat model of IDD induced by acupuncture, and the intervertebral disc height, histological changes, and extracellular matrix synthesis were observed. Finally, to elucidate the mechanisms underlying the quiescent state of NPSCs, the metabolic patterns of the cells were investigated through metabolomics. The results revealed that quiescent NPSCs decreased apoptosis and increased cell survival when compared to proliferating NPSCs both in vitro and in vivo, as well as maintained the disc height and histological structure significantly better than that by proliferating NPSCs. Furthermore, quiescent NPSCs have generally downregulated metabolism and reduced energy requirements in response to a switch to a nutrient-deficient environment. These findings support that quiescence preconditioning maintains the proliferation and biological function potential of NPSCs, increases cell survival under the extreme environment of IVD, and further alleviates IDD via adaptive metabolic patterns.

Candidate genes potentially involved in molting and body size reduction in the male of the horned gall aphid, Schlechtendalia chinensis

In general, insects grow (increase in body size) through molting. To the opposite, the body size of the males of the horned gall aphid, Schlechtendalia chinensis, gets smaller after molting and as they age. To understand the molecular bases of this rare phenomenon, transcriptomes were generated from 1-5 days old male and the data were analyzed via a weighted gene co-expression network analysis (WGCNA). A total of 15 partitioned modules with different topological overlaps were obtained, and four modules were identified as highly significant for male body length (p < 0.05). Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis suggested that a portion of genes in the four modules are likely involved in autophagy and apoptosis. In addition, a total of 40 hub genes were obtained in the four modules, and among them eight genes were highly expressed in males compared to individuals of other generations of S. chinensis. These eight genes were associated with autophagy and apoptosis. Our results reveal the unique negative growth phenomenon in male S. chinensis after molting, and also suggest that the male S. chinensis with no ability to feed probably decompose their own substances via autophagy and apoptosis to provide energy for life activities such as germ cell development.

Update on the Correlation Between Mitochondrial Dysfunction and Intervertebral Disk Degeneration

Low back pain (LBP) is a common disorder in orthopedic outpatients, affecting people of all ages, and some patients may develop chronic LBP. As a complex organelle, mitochondria are not only energy workstations but also regulate cell senescence, apoptosis, and homeostasis. Mitochondrial dysfunction promotes disk degeneration by affecting a variety of pathophysiological processes, including oxidative stress, mitophagy, mitochondrial homeostasis, cellular senescence, and cell death. We review the molecular mechanisms underlying the relationship between mitochondrial dysfunction and intervertebral disk degeneration (IDD) to provide a theoretical basis for IDD treatment using pharmacological or tissue-engineering approaches.

Development of a Perfusion Reactor for Intervertebral Disk Regeneration

A tissue-engineered biological disk replacement has been proposed as a promising approach for the treatment of degenerative disk disease. A perfusion bioreactor would be a logical consideration to facilitate this scale-up as such reactors have been shown to improve nutrient delivery and provide beneficial mechanical forces that support the cultivation of large three-dimensional constructs. It was hypothesized that perfusion culture of tissue-engineered intervertebral disk (IVD) tissues would be capable of generating outer annulus fibrosus (oAF) and nucleus pulposus (NP) tissues comparable with established spinner reactor or static cultures, respectively, without compromising cellular viability, nutrient delivery, and tissue formation. In this study, the perfusion grown oAF and NP tissues did not show a significant difference in extracellular matrix (ECM) quantity or cellular phenotype when compared with their control conditions. In addition, they maintained cellular viability at the center core of the tissues and received enhanced diffusion of medium throughout the tissue when compared with static conditions. This study lays the groundwork for future studies to grow an entire IVD tissue to a physiologically relevant size.

Mitochondrial quality control in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a common and early-onset pathogenesis in the human lifespan that can increase the risk of low back pain. More clarification of the molecular mechanisms associated with the onset and progression of IDD is likely to help establish novel preventive and therapeutic strategies. Recently, mitochondria have been increasingly recognized as participants in regulating glycolytic metabolism, which has historically been regarded as the main metabolic pathway in intervertebral discs due to their avascular properties. Indeed, mitochondrial structural and functional disruption has been observed in degenerated nucleus pulposus (NP) cells and intervertebral discs. Multilevel and well-orchestrated strategies, namely, mitochondrial quality control (MQC), are involved in the maintenance of mitochondrial integrity, mitochondrial proteostasis, the mitochondrial antioxidant system, mitochondrial dynamics, mitophagy, and mitochondrial biogenesis. Here, we address the key evidence and current knowledge of the role of mitochondrial function in the IDD process and consider how MQC strategies contribute to the protective and detrimental properties of mitochondria in NP cell function. The relevant potential therapeutic treatments targeting MQC for IDD intervention are also summarized. Further clarification of the functional and synergistic mechanisms among MQC mechanisms may provide useful clues for use in developing novel IDD treatments.

Transcription-Based Multidimensional Regulation of Fatty Acid Metabolism by HIF1α in Renal Tubules

Lipid metabolism plays a basic role in renal physiology, especially in tubules. Hypoxia and hypoxia-induced factor (HIF) activation are common in renal diseases; however, the relationship between HIF and tubular lipid metabolism is poorly understood. Using prolyl hydroxylase inhibitor roxadustat (FG-4592), we verified and further explored the relationship between sustained HIF1α activation and lipid accumulation in cultured tubular cells. A transcriptome and chromatin immunoprecipitation sequencing analysis revealed that HIF1α directly regulates the expression of a number of genes possibly affecting lipid metabolism, including those associated with mitochondrial function. HIF1α activation suppressed fatty acid (FA) mobilization from lipid droplets (LDs) and extracellular FA uptake. Moreover, HIF1α decreased FA oxidation and ATP production. A lipidomics analysis showed that FG-4592 caused strong triglyceride (TG) accumulation and increased some types of phospholipids with polyunsaturated fatty acyl (PUFA) chains, as well as several proinflammatory lipids. Nevertheless, the overall FA level was maintained. Thus, our study indicated that HIF1α reduced the FA supply and utilization and reconstructed the composition of lipids in tubules, which is likely a part of hypoxic adaptation but could also be involved in pathological processes in the kidney.

Major ceRNA regulation and key metabolic signature analysis of intervertebral disc degeneration

Background and objective

Intervertebral disc degeneration (IDD) is a complex multifactorial and irreversible pathological process. In IDD, multiple competing endogenous RNAs (ceRNA, including mRNA, lncRNA, and pseudogenes) can compete to bind with miRNAs. However, the potential metabolic signatures in nucleus pulposus (NP) cells remain poorly understood. This study investigated key metabolic genes and the ceRNA regulatory mechanisms in the pathogenesis of IDD based on microarray datasets.

Methods

We retrieved and downloaded four independent IDD microarray datasets from the Gene Expression Omnibus. Combining the predicted interactions from online databases (miRcode, miRDB, miRTarBase, and TargetScan), differentially expressed lncRNAs (DElncRNAs), miRNAs (DEmiRNAs), and mRNAs (DEmRNAs) were identified. A ceRNA network was constructed and annotated using GO and KEGG pathway enrichment analyses. Moreover, we searched the online metabolic gene set and used support vector machine (SVM) to find the critical metabolic DEmRNA(s) and other DERNAs. Differential gene expression was validated with a merged dataset.

Results

A total of 45 DEmRNAs, 36 DElncRNAs, and only one DEmiRNA (miR-338-3p) were identified in the IDD microarray datasets. GO and KEGG pathway enrichment analyses revealed that the DEmRNAs were predominantly enriched in the PI3K-Akt signaling pathway, MAPK signaling pathway, IL-17 signaling pathway, apoptosis, and cellular response to oxidative stress. Based on SVM screening, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK/FBPase) 2 is the critical metabolic gene with lower expression in IDD, and AC063977.6 is the key lncRNA with lower expression in IDD. The ceRNA hypothesis suggests that AC063977.6, miR-338-3p (high expression), and PFKFB2 are dysregulated as an axis in IDD.

Conclusions

The results suggest that lncRNA AC063977.6 correlate with PFKFB2, the vital metabolic signature gene, via targeting miR-338-3p during IDD pathogenesis. The current study may shed light on unraveling the pathogenesis of IDD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04109-8.

Characterizing Ischaemic Tolerance in Rat Pheochromocytoma (PC12) Cells and Primary Rat Neurons

Preconditioning tissue with sublethal ischaemia or hypoxia can confer tolerance (protection) against subsequent ischaemic challenge. In vitro ischaemic preconditioning (IPC) is typically achieved through oxygen glucose deprivation (OGD), whereas hypoxic preconditioning (HPC) involves oxygen deprivation (OD) alone. Here, we report the effects of preconditioning of OGD, OD or glucose deprivation (GD) in ischaemic tolerance models with PC12 cells and primary rat neurons. PC12 cells preconditioned (4 h) with GD or OGD, but not OD, prior to reperfusion (24 h) then ischaemic challenge (OGD 6 h), showed greater mitochondrial activity, reduced cytotoxicity and decreased apoptosis, compared to sham preconditioned PC12 cells. Furthermore, 4 h preconditioning with reduced glucose (0.565 g/L, reduced from 4.5 g/L) conferred protective effects, but not for higher concentrations (1.125 or 2.25 g/L). Preconditioning (4 h) with OGD, but not OD or GD, induced stabilization of hypoxia inducible factor 1α (HIF1α) and upregulation of HIF1 downstream genes (Vegf, Glut1, Pfkfb3 and Ldha). In primary rat neurons, only OGD preconditioning (4 h) conferred neuroprotection. OGD preconditioning (4 h) induced stabilization of HIF1α and upregulation of HIF1 downstream genes (Vegf, Phd2 and Bnip3). In conclusion, OGD preconditioning (4 h) followed by 24 h reperfusion induced ischaemic tolerance (against OGD, 6 h) in both PC12 cells and primary rat neurons. The OGD preconditioning protection is associated with HIF1α stabilization and upregulation of HIF1 downstream gene expression. GD preconditioning (4 h) leads to protection in PC12 cells, but not in neurons. This GD preconditioning-induced protection was not associated with HIF1α stabilization.

Mitophagy in degenerative joint diseases

Mitochondrial dysfunction is involved in aging and multiple degenerative diseases, including intervertebral disc degeneration (IVDD) and osteoarthritis (OA). Thus, the maintenance of mitochondria homeostasis and function is important. Mitophagy, a process that selectively clears damaged or dysfunctional mitochondria through autophagic machinery, functions to maintain mitochondrial quality control and homeostasis. IVDD and OA are similar joint diseases involving the degradation of cartilaginous tissues that are mainly caused by oxidative stress, cell apoptosis and extracellular matrix (ECM) degradation. Over the past decade, accumulating evidence indicates the essential role of mitophagy in the pathogenesis of IVDD and OA. Importantly, strategies by the regulation of mitophagy exert beneficial effects in the pre-clinical experiments. Given the importance and novelty of mitophagy, we provide an overview of mitophagy pathways and discuss the roles of mitophagy in IVDD and OA. We also highlight the potential of targeting mitophagy for the treatment of degenerative joint diseases.

Abbreviations: AD: Alzheimer disease; AF: annulus fibrosus; ADORA2A/A2AR: adenosine A2a receptor; AMBRA1: autophagy and beclin 1 regulator 1; BMSCs: bone marrow mesenchymal stem cells; BNIP3: BCL2 interacting protein 3; BNIP3L/NIX: BCL2/adenovirus E1B interacting protein 3-like; CDH6: cadherin 6; CEP: cartilaginous endplates; circRNA: circular RNA; DNM1L/DRP1: dynamin 1-like; ECM: extracellular matrix; HIF1A: hypoxia inducible factor 1: alpha subunit; IL1B: interleukin 1 beta; IMM: inner mitochondrial membranes; IVDD: intervertebral disc degeneration; MAPK8/JNK: mitogen-activated protein kinase 8; MFN1: mitofusin 1; MFN2: mitofusin 2; MIA: monosodium iodoacetate; RHOT/MIRO: ras homolog family member T; MMP: mitochondrial transmembrane potential; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; NFE2L2: nuclear factor: erythroid 2 like 2; NP: nucleus pulposus; OA: osteoarthritis; OPA1: OPA1: mitochondrial dynamin like GTPase; OPTN: optineurin; PRKN: parkin RBR E3 ubiquitin protein ligase; PD: Parkinson disease; PGAM5: PGAM family member 5; PPARGC1A/PGC-1A: peroxisome proliferator activated receptor: gamma: coactivator 1 alpha; PHF23: PHD finger protein 23; PINK1: PTEN induced putative kinase 1; ROS: reactive oxygen species; SfMSCs: synovial fluid MSCs; SIRT1: sirtuin 1; SIRT2: sirtuin 2; SIRT3: sirtuin 3; SQSTM1/p62: sequestosome 1; TNF: tumor necrosis factor; Ub: ubiquitin; UBL: ubiquitin-like; VDAC: voltage-dependent anion channel.

Mesenchymal stem cell‑derived extracellular vesicles prevent neural stem cell hypoxia injury via promoting miR‑210‑3p expression

Neural stem cells (NSCs) have the potential to give rise to offspring cells and hypoxic injury can impair the function of NSCs. The present study investigated the effects of mesenchymal stem cell (MSC)-derived extracellular vesicles (EVs) on NSC injury, as well as the underlying mechanisms. MSC-EVs were isolated and identified via morphological and particle size analysis. Cobalt chloride was used to establish a hypoxic injury model in NSCs. Terminal deoxynucleotidyl transferase dUTP nick end labeling assay was conducted to detect apoptosis. Reverse transcription-quantitative PCR was performed to detect the expression levels of miR-210-3p, and western blotting was used to detect the expression levels of apoptosis-inducing factor (AIF) and Bcl-2 19 kDa interacting protein (BNIP3). Compared with the control group, NSC apoptosis, and the expression of miR-210-3p, AIF and BNIP3 were significantly higher in the cobalt chloride-induced hypoxia group. By contrast, treatment with MSC-EVs further increased miR-210-3p expression levels, but reduced NSC apoptosis and the expression levels of AIF and BNIP3 compared with the model group (P<0.05). In addition, miR-210-3p inhibitor reduced miR-210-3p expression, but promoted hypoxia-induced apoptosis and the expression levels of AIF and BNIP3 compared with the model group (P<0.05). Collectively, the results suggested that MSC-EVs prevented NSC hypoxia injury by promoting miR-210-3p expression, which might reduce AIF and BNIP3 expression levels and NSC apoptosis.

The mitochondria-targeted anti-oxidant MitoQ protects against intervertebral disc degeneration by ameliorating mitochondrial dysfunction and redox imbalance

Objective

Mitochondrial dysfunction, oxidative stress and nucleus pulposus (NP) cell apoptosis are important contributors to the development and pathogenesis of intervertebral disc degeneration (IDD). Here, we comprehensively evaluated the effects of mitochondrial dynamics, mitophagic flux and Nrf2 signalling on the mitochondrial quality control, ROS production and NP cell survival in in vitro and ex vivo compression models of IDD and explored the effects of the mitochondria‐targeted anti‐oxidant MitoQ and its mechanism.

Material and methods

Human NP cells were exposed to mechanical compression to mimic pathological conditions.

Results

Compression promoted oxidative stress, mitochondrial dysfunction and NP cell apoptosis. Mechanistically, compression disrupted the mitochondrial fission/fusion balance, inducing fatal fission. Concomitantly, PINK1/Parkin‐mediated mitophagy was activated, whereas mitophagic flux was blocked. Nrf2 anti‐oxidant pathway was insufficiently activated. These caused the damaged mitochondria accumulation and persistent oxidative damage. Moreover, MitoQ restored the mitochondrial dynamics balance, alleviated the impairment of mitophagosome‐lysosome fusion and lysosomal function and enhanced the Nrf2 activity. Consequently, damaged mitochondria were eliminated, redox balance was improved, and cell survival increased. Additionally, MitoQ alleviated IDD in an ex vivo rat compression model.

Conclusions

These findings suggest that comodulation of mitochondrial dynamics, mitophagic flux and Nrf2 signalling alleviates sustained mitochondrial dysfunction and oxidative stress and represents a promising therapeutic strategy for IDD; furthermore, our results provide evidence that MitoQ might serve as an effective therapeutic agent for this disorder.

Screening of key candidate genes and pathways for osteocytes involved in the differential response to different types of mechanical stimulation using a bioinformatics analysis

This study aimed to predict the key genes and pathways that are activated when different types of mechanical loading are applied to osteocytes. mRNA expression datasets (series number of GSE62128 and GSE42874) were obtained from Gene Expression Omnibus database (GEO). High gravity-treated osteocytic MLO-Y4 cell-line samples from GSE62128 (Set1), and fluid flow-treated MLO-Y4 samples from GSE42874 (Set2) were employed. After identifying the differentially expressed genes (DEGs), functional enrichment was performed. The common DEGs between Set1 and Set2 were considered as key DEGs, then a protein-protein interaction (PPI) network was constructed using the minimal nodes from all of the DEGs in Set1 and Set2, which linked most of the key DEGs. Several open source software programs were employed to process and analyze the original data. The bioinformatic results and the biological meaning were validated by in vitro experiments. High gravity and fluid flow induced opposite expression trends in the key DEGs. The hypoxia-related biological process and signaling pathway were the common functional enrichment terms among the DEGs from Set1, Set2 and the PPI network. The expression of almost all the key DEGs (Pdk1, Ccng2, Eno2, Egln1, Higd1a, Slc5a3 and Mxi1) were mechano-sensitive. Eno2 was identified as the hub gene in the PPI network. Eno2 knockdown results in expression changes of some other key DEGs (Pdk1, Mxi1 and Higd1a). Our findings indicated that the hypoxia response might have an important role in the differential responses of osteocytes to the different types of mechanical force.

The neuroprotective mechanism of 2-arachidonoylglycerol 2-AG against non-caspase-dependent apoptosis in mice hippocampal neurons following MCAO

OBJECTIVE

In this study, the neuroprotective mechanism of 2-arachidonoylglycerol 2-AG against non-caspase-dependent apoptosis in mice hippocampal neurons following MCAO was investigated.

METHOD

One hundred and fifty healthy clean male C57BL/6 mice were randomly divided into 3 groups: sham group, model group and 2-AG treatment group, 50 mice in each group. A modified Zea Longa method was used to establish a model of middle cerebral artery occlusion (MCAO) in mice. The apoptosis rate and mitochondrial membrane potential of hippocampal nerve cells were measured by flow cytometry. The mRNA expressions of AIF, Endo G and BNIP3 in hippocampal tissues were determined by qPCR. Western blot was used to determine the protein expressions of AIF, Endo G and BNIP3 in the mitochondria of hippocampal tissue.

RESULTS

The apoptosis rate of hippocampal neurons in the group treated with 2-AG was significantly lower than that of the model (P<0.01), which indicated that 2-AG could inhibit the apoptosis of hippocampal neurons induced by MCAO. However, the mitochondrial membrane potential of hippocampal neurons in the group treated with 2-AG was significantly higher than that of the model (P<0.01), indicating that 2-AG could improve the mitochondrial membrane potential of hippocampal neurons in MCAO mice. Real-time quantitative PCR (qPCR) showed that 2-AG could inhibit the gene expressions of AIF, Endo G and BNIP3 in hippocampal tissues. Western blot results showed that 2-AG could inhibit the secretions of AIF, Endo G and BNIP3 into cytoplasm in mitochondria.

CONCLUSION

Endocannabinoids 2-AG had a protective effect on neurons injury, and the mechanism was possibly associated with the protection of the brain nerve cells in the hippocampus and the integrity of the mitochondrial function. Endocannabinoids 2-AG may inhibit the non-caspase-dependent apoptosis pathway, so as to exert its nerve protective effect.