Increasing UCP2 expression and decreasing NOX1/4 expression maintain chondrocyte phenotype by reducing reactive oxygen species production

Identification and Verification of Hub Mitochondrial Dysfunction Genes in Osteoarthritis Based on Bioinformatics Analysis

Objective

Age-related mitochondrial dysfunction and associated oxidative stress may contribute to the development of osteoarthritis. The aim of this study was to identify hub genes associated with mitochondrial dysfunction in osteoarthritis (OA) patients, helping predict the risk of OA, and revealing the mechanism of OA progression.

Methods

OA expression data and mitochondrial dysfunction genes were downloaded from GEO (GSE55235, GSE82107, and GSE114007) and GeneCard databases. The differentially expressed mitochondrial dysfunction genes (DEMDFGs) between OA and control samples were screened. Gene ontology (GO) and Kyoto encyclopedia of genes and genomes pathways were analyzed for DEMDFGs. The hub genes were determined by WGCNA and LASSO regression analysis. ROC curves manifested the diagnostic efficacy of each hub gene. A nomogram model was constructed and validated to predict OA risk. The expression of hub genes in OA and normal chondrocytes was verified by external datasets, qRT-PCR and western blotting.

Results

A total of 31 DEMDFGs were identified, with 15 genes upregulated and 16 genes downregulated. GO functional enrichment analysis revealed that DEMDFGs were enriched in biological processes related to energy metabolism and cellular respiration. By employing weighted gene coexpression network analysis, we identified four distinct coexpression modules, among which the blue module exhibited the strongest correlation with OA. The intersection between DEMDFGs and this module yielded eight candidate genes. After LASSO analysis of the data, four hub genes (ACADL, CYBA, SLC19A2, and UCP2) were identified as potential biomarkers for OA. The expression levels of these four genes were externally validated in the GSE114007 dataset. And the biologically differential expression of these four genes has been verified in OA and normal chondrocytes. Moreover, the four hub genes had good sensitivity and specificity by ROC curve analysis, and the risk model constructed with these four genes showed promising performance. In conclusion, our study may provide novel mitochondrial dysfunction hub genes with potential clinical applications for understanding the pathology, diagnosis, and treatment of OA.

PGC-1α in osteoarthritic chondrocytes: From mechanism to target of action

Osteoarthritis (OA) is one of the most common degenerative joint diseases, often involving the entire joint. The degeneration of articular cartilage is an important feature of OA, and there is growing evidence that the mitochondrial biogenesis master regulator peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) exert a chondroprotective effect. PGC-1α delays the development and progression of OA by affecting mitochondrial biogenesis, oxidative stress, mitophagy and mitochondrial DNA (mtDNA) replication in chondrocytes. In addition, PGC-1α can regulate the metabolic abnormalities of OA chondrocytes and inhibit chondrocyte apoptosis. In this paper, we review the regulatory mechanisms of PGC-1α and its effects on OA chondrocytes, and introduce potential drugs and novel nanohybrid for the treatment of OA which act by affecting the activity of PGC-1α. This information will help to further elucidate the pathogenesis of OA and provide new ideas for the development of therapeutic strategies for OA.

Deletion of Nox4 enhances remyelination following cuprizone-induced demyelination by increasing phagocytic capacity of microglia and macrophages in mice

NOX4 is a major reactive oxygen species-producing enzyme that modulates cell stress responses. We here examined the effect of Nox4 deletion on demyelination-remyelination, the most common pathological change in the brain. We used a model of cuprizone (CPZ)-associated demyelination-remyelination in wild-type and Nox4-deficient (Nox4^-/- ) mice. While the CPZ-induced demyelination in the corpus callosum after 4 weeks of CPZ intoxication was slightly less pronounced in Nox4^-/- mice than that in wild-type mice, remyelination following CPZ withdrawal was significantly enhanced in Nox4^-/- mice with an increased accumulation of IBA1-positive microglia/macrophages in the demyelinating corpus callosum. Consistently, locomotor function, as assessed by the beam walking test, was significantly better during the remyelination phase in Nox4^-/- mice. Nox4 deletion did not affect autonomous growth of primary-culture oligodendrocyte precursor cells. Although Nox4 expression was higher in cultured macrophages than in microglia, Nox4^-/- microglia and macrophages both showed enhanced phagocytic capacity of myelin debris and produced increased amounts of trophic factors upon phagocytosis. The expression of trophic factors was higher, in parallel with the accumulation of IBA1-positive cells, in the corpus callosum in Nox4^-/- mice than that in wild-type mice. Nox4 deletion suppressed phagocytosis-induced increase in mitochondrial membrane potential, enhancing phagocytic capacity of macrophages. Treatment with culture medium of Nox4^-/- macrophages engulfing myelin debris, but not that of Nox4^-/- astrocytes, enhanced cell growth and expression of myelin-associated proteins in cultured oligodendrocyte precursor cells. Collectively, Nox4 deletion promoted remyelination after CPZ-induced demyelination by enhancing microglia/macrophage-mediated clearance of myelin debris and the production of trophic factors leading to oligodendrogenesis.

Damage-induced pyroptosis drives endog thymic regeneration via induction of Foxn1 by purinergic receptor activation

Endogenous thymic regeneration is a crucial process that allows for the renewal of immune competence following stress, infection or cytoreductive conditioning. Fully understanding the molecular mechanisms driving regeneration will uncover therapeutic targets to enhance regeneration. We previously demonstrated that high levels of homeostatic apoptosis suppress regeneration and that a reduction in the presence of damage-induced apoptotic thymocytes facilitates regeneration. Here we identified that cell-specific metabolic remodeling after ionizing radiation steers thymocytes towards mitochondrial-driven pyroptotic cell death. We further identified that a key damage-associated molecular pattern (DAMP), ATP, stimulates the cell surface purinergic receptor P2Y2 on cortical thymic epithelial cells (cTECs) acutely after damage, enhancing expression of Foxn1, the critical thymic transcription factor. Targeting the P2Y2 receptor with the agonist UTPγS promotes rapid regeneration of the thymus in vivo following acute damage. Together these data demonstrate that intrinsic metabolic regulation of pyruvate processing is a critical process driving thymus repair and identifies the P2Y2 receptor as a novel molecular therapeutic target to enhance thymus regeneration.

Novel biomarkers of intervertebral disc cells and evidence of stem cells in the intervertebral disc

OBJECTIVE

Rat intervertebral disc (IVD) is one of the most commonly used and cost-effective alternative models for human IVD. Many IVD related clinical studies need to be pre-tested on rat IVDs. However, studies on the heterogeneous cell clusters of the rat IVD are inadequate, and a further understanding of the marker genes and cell phenotypes of healthy mature IVD cells is essential.

METHODS

In this study, we used the 10X Genomics technology to analyze the single-cell transcriptome of purified wild-type rat IVDs.

RESULTS

We identified potentially new gene markers of IVDs via single-cell sequencing. Based on the unsupervised cluster analysis of 13,578 single-cell transcripts, 3 known IVD cell types were identified. We provided a complete single-cell gene expression map of the IVD. Immunohistochemical and immunofluorescence images of rat disc sections confirmed the new marker genes of all cell types. One group of heterologous cell groups expressed multi-functional stem cell (MSC)-specific genes, indicating the stem cell potential of IVD cells.

CONCLUSION

We provided the phenotype and marker genes of IVD cells at the single-cell level, reconfirmed existing data, and proposed new marker genes, including MSC marker genes. By identifying more accurate target cells and genes, our results pave the way for further study of the response of individual disc cells to disease states and provide the basis for future disc regeneration therapies.

Protective Role of UCP2 in Oxidative Stress and Apoptosis during the Silent Phase of an Experimental Model of Epilepsy Induced by Pilocarpine

Neuroprotection is a desirable process in many neurological disorders, yet complex mechanisms involved in this field are not completely understood. The pilocarpine epilepsy model causes potent, seizure-induced excitotoxicity cell death and mitochondria impairment. The present study is aimed at investigating the role of UCP2, a ROS negative regulator, in the neuroprotection after cholinergic insult. Our data demonstrated that UCP2 expression was augmented in the rat hippocampus 3 days after status epilepticus (SE), reaching a peak on the fifth day, then returning to basal levels. Concomitantly, phospho-AKT expression levels were higher in the hippocampus during the early silent phase (5 days after SE). Additionally, it was demonstrated that the blockade of UCP2 by antisense oligonucleotides (ASO) in SE rats successfully diminished both UCP2 mRNA and protein contents. SE ASO rats presented increased mitochondrial proapoptotic factor expression, caspase-3 activity, inflammatory cytokine expression, and ROS formation. Moreover, ASO treatment diminished p-AKT expression and antioxidant enzyme activities after pilocarpine insult. In conclusion, the present results highlight the neuroprotective actions of UCP2, acting in the inhibition of apoptotic factors and oxidative stress, to increase neuron survival after SE onset.