Mitochondrial stress and redox failure in steroid-associated osteonecrosis

Bioinformatics proved the existence of potential hub genes activating autophagy to participate in cartilage degeneration in osteonecrosis of the femoral head

The obvious degeneration of articular cartilage occurs in the late stage of osteonecrosis of the femoral head (ONFH), which aggravates the condition of ONFH. This study aimed to demonstrate aberrant activation of autophagy processes in ONFH chondrocytes through bioinformatics and to predict and identify relevant hub genes and pathways. Differentially expressed genes (DEGs) were identified using R software in the GSE74089 dataset from the GEO database. DEGs were crossed with the Human Autophagy Database (HADb) autophagy genes to screen out autophagy-related differential genes (AT-DEGs). GSEA, GSVA, GO, and KEGG pathway enrichment analyses of AT-DEGs were performed. The STRING database was used to analyze the protein-protein interaction (PPI) of the AT-DEGs network, and the MCODE and CytoHubba plugin in the Cytoscape software was used to analyze the key gene cluster module and screen the hub genes. The PPI network of hub genes was constructed using the GeneMANIA database, and functional enrichment and gene connectivity categories were analyzed. The expression levels of hub genes of related genes in the ONFH patients were verified in the dataset GSE123568, and the protein expression was verified by immunohistochemistry in tissues. The analysis of DEGs revealed abnormal autophagy in ONFH cartilage. AT-DEGs in ONFH have special enrichment in macroautophagy, autophagosome membrane, and phosphatidylinositol-3-phosphate binding. In the GSE123568 dataset, it was also found that ATG2B, ATG4B, and UVRAG were all significantly upregulated in ONFH patients. By immunohistochemistry, it was verified that ATG2B, ATG4B, and UVRAG were significantly overexpressed. These three genes regulate the occurrence and extension of autophagosomes through the PI3KC3C pathway. Finally, we determined that chondrocytes in ONFH undergo positive regulation of autophagy through the corresponding pathways involved in three genes: ATG2B, ATG4B, and UVRAG.

Inhibition of insulin degrading enzyme suppresses osteoclast hyperactivity via enhancing Nrf2-dependent antioxidant response in glucocorticoid-induced osteonecrosis of the femoral head

BACKGROUND

Osteoclast hyperactivation due to the pathological overproduction of reactive oxygen species (ROS) stimulated by glucocorticoids (GCs) is one of the key drivers behind glucocorticoid-induced osteonecrosis of the femoral head (GIONFH). The insulin degrading enzyme (IDE), a conserved Zn2+ metallo-endopeptidase, facilitates the DNA binding of glucocorticoid receptor and plays a substantial role in steroid hormone-related signaling pathways. However, the potential role of IDE in the pathogenesis of GIONFH is yet undefined.

METHODS

In this study, we employed network pharmacology and bioinformatics analysis to explore the impact of IDE inhibition on GIONFH with 6bK as an inhibitory agent. Further evidence was collected through in vitro osteoclastogenesis experiments and in vivo evaluations involving methylprednisolone (MPS)-induced GIONFH mouse model.

RESULTS

Enrichment analysis indicated a potential role of 6bK in redox regulation amid GIONFH development. In vitro findings revealed that 6bK could attenuate GCs-stimulated overactivation of osteoclast differentiation by interfering with the transcription and expression of key osteoclastic genes (Traf6, Nfatc1, and Ctsk). The use of an H2DCFDA probe and subsequent WB assays introduced the inhibitory effects of 6bK on osteoclastogenesis, linked with the activation of the nuclear factor erythroid-derived 2-like 2 (Nrf2)-mediated antioxidant system. Furthermore, Micro-CT scans validated that 6bK could alleviate GIONFH in MPS-induced mouse models.

CONCLUSIONS

Our findings suggest that 6bK suppresses osteoclast hyperactivity in GCs-rich environment. This is achieved by reducing the accumulation of intracellular ROS via promoting the Nrf2-mediated antioxidant system, thus implying that IDE could be a promising therapeutic target for GIONFH.

Mesenchymal Stem Cells Preconditioned with Hypoxia and Dexamethasone Promote Osteoblast Differentiation Under Stress Conditions

Bone marrow-derived mesenchymal stem cells (MSCs), which are capable of differentiating into osteoblasts, are used in effective regenerative therapies. MSCs must be prompted to differentiate into osteoblasts for MSC transplantation to be effective. In this study, osteoblast differentiation markers involved in bone formation were evaluated to investigate the stress resistance of bone marrow-derived rat MSCs to dexamethasone and hypoxia and their ability to differentiate into osteoblasts. MSCs were allowed to differentiate into osteoblasts for 21 days in three different environments (dexamethasone treatment, hypoxic conditions [1% oxygen], or both). Osteoblast differentiation potential was evaluated according to alkaline phosphatase levels and a mineralisation assay. Immunofluorescence staining was used to determine the protein expression of the osteoblast differentiation markers type I collagen and osteopontin. MSCs differentiated into osteoblasts under hypoxic conditions but differentiated more slowly upon treatment with dexamethasone and dexamethasone plus hypoxia relative to the control. MSCs preconditioned with dexamethasone or hypoxia and then allowed to differentiate into osteoblasts under similar conditions differentiated comparably to control MSCs. MSCs that developed resistance to dexamethasone or hypoxia differentiated more quickly into osteoblasts than those that did not. The findings suggest that increasing the resistance of MSCs to stress by preconditioning them via dexamethasone or hypoxia exposure could result in more rapid differentiation into osteoblasts following transplantation.

Selenium nanoparticles/carboxymethyl chitosan/alginate antioxidant hydrogel for treating steroid-induced osteonecrosis of the femoral head

Oxidative stress plays a crucial role in steroid-induced osteonecrosis of the femoral head (SONFH). Although several antioxidant strategies have been investigated for treating SONFH, their antioxidant efficiencies and therapeutic effects remain unsatisfactory. Here, we developed a selenium nanoparticles/carboxymethyl chitosan/alginate (SeNPs/CMC/Alg) antioxidant hydrogel and evaluated its ability to treat SONFH. In vitro assays indicated that the SeNPs/CMC/Alg hydrogel exhibited excellent properties, such as low cytotoxicity, sustained SeNPs release, and favorable antioxidant activity. Under oxidative stress, the SeNPs/CMC/Alg hydrogel promoted reactive oxygen species (ROS) elimination and enhanced the osteogenic and proangiogenic abilities of bone marrow mesenchymal stem cells (BMSCs). After establishing a rabbit model of SONFH, the SeNPs/CMC/Alg hydrogel was transplanted into the femoral head after core decompression (CD) surgery. Radiographic and histological analyses revealed that the hydrogel treatment alleviated SONFH by eliminating ROS and promoting osteogenesis and angiogenesis compared to those in the CD and CMC/Alg groups. In vitro and in vivo studies indicated that the Wnt/β-catenin signaling pathway was activated by the SeNPs/CMC/Alg hydrogel in both hydrogen peroxide-conditioned BMSCs and necrotic femoral heads. These findings indicate that local transplantation of the SeNPs/CMC/Alg hydrogel is beneficial for treating SONFH, as it promotes ROS elimination and activation of the Wnt/β-catenin signaling pathway.

Spontaneous, simultaneous bilateral osteonecrosis of the femoral heads in a patient with sideroblastic anaemia with B-cell immunodeficiency, periodic fever and developmental delay syndrome

Sideroblastic anaemia with B-cell immunodeficiency, periodic fever and developmental delay is a recently described, rare syndrome characterised by numerous manifestations underpinned by mutations in transfer RNA nucleotidyltransferase. The pathogenesis arises from mitochondrial dysfunction, with impaired intracellular stress response, deficient metabolism and cellular and systemic inflammation. This yields multiorgan dysfunction and early death in many patients with survivors suffering significant disability and morbidity. New cases, often youths, are still being described, expanding the horizon of recognisable phenotypes. We present a mature patient with spontaneous bilateral hip osteonecrosis that likely arises from the impaired RNA quality control and inflammation caused by this syndrome.

Inhibitory effect of taurine on rotator cuff degeneration via mitochondrial protection

OBJECTIVES

Degenerative rotator cuff tears do not heal spontaneously, necessitating surgical intervention. This makes prevention crucial, but effective prophylactic measures are currently lacking. Oxidative stress has recently been implicated as a cause of degenerative rotator cuff tears, while mitochondrial injury has been reported in the development of age-related rotator cuff degeneration. Taurine, which has antioxidant properties, has been found to be effective in the treatment of various mitochondrial abnormalities. This prompted us to investigate the inhibitory effect of taurine and some other antioxidants against rotator cuff degeneration using tenocytes.

METHODS

Hydrogen peroxide (H₂O₂, 2 mM) was added to tenocytes in medium with 0.8 µM taurine (Group TAU), medium with 100 µM α-tocopherol (Group E), and medium with 150 µM ascorbic acid (Group C), then each medium was cultured for 24 h. Tenocytes supplemented with 2 mM H₂O₂ alone were similarly cultured for 24 h (Group H₂O₂). In each group, immunostaining was performed for the oxidative stress marker 8-hydroxy-2'-deoxyguanosine and advanced glycation end products (AGE), which contribute to the development of age-related rotator cuff degeneration. In addition, levels of reactive oxygen species were measured using a cell-based assay kit, and results were compared. Immunostaining was also performed for indices of apoptosis (caspase-9, cleaved caspase-3 and Bcl-2), and Western blotting was used to quantify activation of caspase-9 at an early stage in each group.

RESULTS

Oxidative stress and AGE levels were decreased in the E and C groups. Levels of all parameters were reduced in the TAU group.

CONCLUSIONS

Taurine showed preventative effects against rotator cuff degeneration. The simple method of administration and paucity of side effects make clinical application easy, and the clear potential as a novel prophylactic strategy against degenerative rotator cuff tear warrants further study.

Calcium chelator BAPTA‑AM protects against iron overload‑induced chondrocyte mitochondrial dysfunction and cartilage degeneration

Osteoarthritis (OA) is a common joint disease that is characterized by cartilage degradation. Iron deposition in the joints is common during the pathogenic progression of OA and recent studies have indicated that iron overload is an important contributor to OA progression. Calcium chelators have been reported to inhibit iron influx via modulating transferrin receptor protein 1 internalization, and they have been identified as a potential approach to the treatment of iron overload‑induced diseases. The aim of the present study was to investigate the effect of calcium chelators on the progression of iron overload‑induced OA. Primary chondrocytes were treated with various concentrations of ferric ammonium citrate (FAC) to mimic iron overload in vitro, followed by co‑treatment with the calcium chelator BAPTA acetoxymethyl ester (BAPTA‑AM). Subsequently, intracellular iron levels, cell viability, reactive oxygen species (ROS) levels, mitochondrial function and morphological changes, as well as MMP levels, were detected using commercial kits. It was demonstrated that FAC treatment significantly promoted chondrocyte apoptosis and the expression of MMPs, and these effects were reversed by co‑treatment with BAPTA‑AM. Moreover, BAPTA‑AM suppressed iron influx into chondrocytes and inhibited iron overload‑induced ROS production and mitochondrial dysfunction. These results indicated that calcium chelators may be of value in the treatment of iron metabolism‑related diseases and iron overload‑induced OA progression.

Integrating Transcriptome-Wide Association Study and mRNA Expression Profiling Identifies Novel Genes Associated With Osteonecrosis of the Femoral Head

Objective

This study aims to identify novel candidate genes associated with osteonecrosis of the femoral head (ONFH).

Methods

A transcriptome-wide association study (TWAS) was performed by integrating the genome-wide association study dataset of osteonecrosis (ON) in the UK Biobank with pre-computed mRNA expression reference weights of muscle skeleton (MS) and blood. The ON-associated genes identified by TWAS were further subjected to gene ontology (GO) analysis by the DAVID tool. Finally, a trans-omics comparative analysis of TWAS and genome-wide mRNA expression profiling was conducted to identify the common genes and the GO terms shared by both DNA-level TWAS and mRNA-level expression profile for ONFH.

Results

TWAS totally identified 564 genes that were with P_TWAS value <0.05 for MS and blood, such as CBX1 (P_TWAS = 0.0001 for MS), SRPK2 (P_TWAS = 0.0002 for blood), and MYO5A (P_TWAS = 0.0005 for blood). After comparing the genes detected by TWAS with the differentially expressed genes identified by mRNA expression profiling, we detected 59 overlapped genes, such as STEAP4 [P_TWAS = 0.0270, FC (fold change)_mRNA = 7.03], RABEP1 (P_TWAS = 0.010, FC_mRNA = 2.22), and MORC3 (P_TWAS = 0.0053, FC_mRNA = 2.92). The GO analysis of TWAS-identified genes discovered 53 GO terms for ON. Further comparing the GO results of TWAS and mRNA expression profiling identified four overlapped GO terms, including cysteine-type endopeptidase activity (P_TWAS = 0.0006, P_mRNA = 0.0227), extracellular space (P_TWAS = 0.0342, P_mRNA = 0.0012), protein binding (P_TWAS = 0.0112, P_mRNA = 0.0106), and ATP binding (P_TWAS = 0.0464, P_mRNA = 0.0033).

Conclusion

Several ONFH-associated genes and GO terms were identified by integrating TWAS and mRNA expression profiling. It provides novel clues to reveal the pathogenesis of ONFH.

Resistance of bone marrow mesenchymal stem cells in a stressed environment - Comparison with osteocyte cells

Introduction: Recently, the efficacy of mesenchymal stem cells (MSCs) mediated by their tissue repair and anti-inflammatory actions in the prevention and therapy of various disorders has been reported. In this research, our attention was focused specifically on the prevention and therapy of glucocorticoid-induced osteonecrosis. We investigated the stress resistance of MSC against glucocorticoid administration and hypoxic stress, which are factors known to induce osteocytic cell death. Materials and Methods: Mouse bone cells (MLO-Y4) and bone-marrow derived mouse MSCs were exposed to dexamethasone (Dex), hypoxia of 1% oxygen or both in vitro. Mitochondrial membrane potentials were estimated by mitochondria labeling with a cell-permeant probe (Mito tracker red); expression of these apoptosis-inducing molecules, oxidative stress marker (8-hydroxy-2'-deoxyguanosine), caspase-3, -9, and two apoptosis-inhibiting molecules, energy-producing ATP synthase (ATP5A) and X-linked inhibitor of apoptosis protein (XIAP), were analyzed by both immunofluorescence and western blot. Results: With exposure to either dexamethasone or hypoxia, MLO-Y4 showed reduced mitochondrial membrane potential, ATP5A and upregulation of 8-OHdG, cleaved caspases and XIAP. Those changes were significantly enhanced by treatment with dexamethasone plus hypoxia. In MSCs, however, mitochondrial membrane potentials were preserved, while no significant changes in the pro-apoptosis or anti-apoptosis molecules analyzed were found even with exposure to both dexamethasone and hypoxia. No such effects induced by treatment with dexamethasone, hypoxia, or both were demonstrated in MSCs at all. Discussion: In osteocyte cells subjected to the double stresses of glucocorticoid administration and a hypoxic environment osteocytic cell death was mediated via mitochondria. In contrast, MSC subjected to the same stressors showed preservation of mitochondrial function and reduced oxidative stress. Accordingly, even under conditions sufficiently stressful to cause the osteocytic cell death in vivo, it was thought that the function of MSC could be preserved, suggesting that in the case of osteonecrosis preventative and therapeutic strategies incorporating their intraosseous implantation may be promising.

The Antioxidant, Anti-Apoptotic, and Proliferative Potency of Argan Oil against Betamethasone-Induced Oxidative Renal Damage in Rats

The present study aimed to investigate the protective effect of argan oil (AO) against nephrotoxic effects following overdose and long-term administration of betamethasone (BM). The phytochemical compositions of AO were assessed using GC/MS. Forty eight male Wister albino rats were divided into six groups and treated for 3 successive weeks. The control group was orally administrated distilled water daily, the BM group received BM (1 mg/kg, IM, day after day), AO/0.5 and AO/1 groups received AO (0.5 mL/kg, 1 mL/kg, orally, daily, respectively), BM + AO/0.5 group and BM + AO/1 group. The results revealed that BM induced hematological changes, including reduction of red blood cells with leukocytosis, neutrophilia, monocytosis, lymphocytopenia, and thrombocytopenia. Moreover, BM caused a significant increase of serum urea and creatinine levels, and renal malondialdehyde and nitric oxide contents with significant decrease of reduced glutathione content. BM also caused vascular, degenerative, and inflammatory histopathological alterations in kidney, along with an increase in the Bax/Bcl-2 ratio, activation of caspase-3, and decrease of proliferating cell nuclear antigen expression. Conversely, the concomitant administration of AO (0.5, 1 mL/kg) with BM ameliorated the aforementioned hematological, biochemical, pathological, and histochemical BM adverse effects. In conclusion, AO has protective effects against BM-induced renal damage, possibly via its antioxidant, anti-apoptotic, and proliferative properties.

Taurine Inhibits Glucocorticoid-Induced Bone Mitochondrial Injury, Preventing Osteonecrosis in Rabbits and Cultured Osteocytes

Mitochondrial injury has recently been implicated in the pathogenesis of glucocorticoid-induced osteonecrosis. Using cultured osteocytes and a rabbit model, we investigated the possibility that taurine (TAU), which is known to play a role in the preservation of mitochondrial function, might also prevent the development of osteonecrosis. To reduplicate the intraosseous environment seen in glucocorticoid-induced osteonecrosis, dexamethasone (Dex) was added to MLO-Y4 cultured in 1% hypoxia (H-D stress environment). An in vitro study was conducted in which changes in mitochondrial transcription factor A (TFAM), a marker of mitochondrial function, and ATP5A produced by mitochondria, induced by the presence/absence of taurine addition were measured. To confirm the effect of taurine in vivo, 15 Japanese White rabbits were administered methylprednisolone (MP) 20 mg/kg as a single injection into the gluteus muscle (MP+/TAU− group), while for 5 consecutive days from the day of MP administration, taurine 100 mg/kg was administered to 15 animals (MP+/TAU+ group). As a control 15 untreated rabbits were also studied. The rabbits in each of the groups were sacrificed on the 14th day after glucocorticoid administration, and the bilateral femora were harvested. Histopathologically, the incidence of osteonecrosis was quantified immunohistochemically by quantifying TFAM and ATP5A expression. In the rabbits exposed to an H-D stress environment and in MP+/TAU− group, TFAM and ATP5A expression markedly decreased. With addition of taurine in the in vitro and in vivo studies, the expression of TFAM and ATP5A was somewhat decreased as compared with Dex−/hypoxia− or MP−/TAU− group, while improvement was noted as compared with Dex+/hypoxia+ or MP+/TAU− group. In rabbits, the incidence of osteonecrosis was 80% in MP+/TAU− group, in contrast to 20% in the taurine administered group (MP+/TAU+), representing a significant decrease. Since taurine was documented to exert a protective effect on mitochondrial function by inhibiting the mitochondrial dysfunction associated with glucocorticoid administration, we speculated that it might also indirectly help to prevent the development of osteonecrosis in this context. Since taurine is already being used clinically, we considered that its clinical application would also likely be smooth.

Desferoxamine protects against glucocorticoid-induced osteonecrosis of the femoral head via activating HIF-1α expression

Glucocorticoid-induced osteonecrosis of the femoral head (GIOFH) is one of the most common complications of glucocorticoid administration. By chelating Fe²⁺ , desferoxamine (DFO) was reported to be able to activate the HIF-1α/VEGF pathway and promote angiogenesis. In the present study, we examined whether DFO administration could promote angiogenesis and bone repair in GIOFH. GIOFH was induced in rats by methylprednisolone in combination with lipopolysaccharide. Bone repair was assessed by histologic analysis and microcomputed tomography (micro-CT). Vascularization was assessed by Microfil perfusion and micro-CT analysis. Immunohistochemical staining was performed to analyze the expression of HIF-1α, VEGF, and CD31. Our in vivo study revealed that DFO increased HIF-1α/VEGF expression and promoted angiogenesis and osteogenesis in GIOFH. Moreover, our in vitro study revealed that DFO restored dexamethone-induced HIF-1α downregulation and angiogenesis inhibition. Besides, our in vitro study also demonstrated that DFO could protect bone marrow-derived stem cells from dexamethone-induced apoptosis and mitochondrial dysfunction by promoting mitophagy and mitochondrial fission. In summary, our data provided useful information for the development of novel therapeutics for management of GIOFH.

Steroid-induced osteonecrosis of the femoral head reveals enhanced reactive oxygen species and hyperactive osteoclasts

Steroid-induced osteonecrosis of the femoral head (ONFH) is a progressive bone disorder which typically results in femoral head collapse and hip joint dysfunction. It is well-accepted that abnormal osteoclast activity contributes to loss of bone structural integrity and subchondral fracture in ONFH. However, the pathophysiologic mechanisms underlying the recruitment and hyperactivation of osteoclasts in ONFH remain incompletely understood. We assessed the changes of reactive oxygen species (ROS) level and subsequent osteoclast alterations in steroid-induced osteonecrotic femoral heads from both patients and rat ONFH models. When compared with healthy neighboring bone, the necrotic region of human femoral head was characterized by robust up-regulated expression of osteoclast-related proteins [cathepsin K and tartrate-resistant acid phosphatase(TRAP)] but pronounced down-regulation of antioxidant enzymes (catalase, γ-glutamylcysteine synthetase [γ-GCSc], and superoxide dismutase 1 [SOD1]). In addition, the ratio of TNFSF11 (encoding RANKL)/TNFRSF11B (encoding OPG) was increased within the necrotic bone. Consistently, in rat ONFH models induced by methylprednisolone (MPSL) and imiquimod (IMI), significant bone loss in the femoral head was observed, attributable to increased numbers of TRAP positive osteoclasts. Furthermore, the decreased expression of antioxidant enzymes observed by immunoblotting was accompanied by increased ex-vivo ROS fluorescence signals of dihydroethidium (DHE) in rat ONFH models. Therefore, this study lends support to the rationale that antioxidant agents may be a promising therapeutic avenue to prevent or mitigate the progression of steroid-induced ONFH by inhibiting ROS level and hyperactive osteoclasts.

Mitochondrial Transcription Factor A added to Osteocytes in a Stressed Environment has a Cytoprotective Effect

The main precipitant of glucocorticoid-associated femoral head osteonecrosis is widely accepted to be an ischemic-hypoxic event, with oxidative stress also as an underlying factor. Mitochondrial DNA is more vulnerable to oxidative injury than the nucleus, and mitochondrial transcription factor A (TFAM), which plays roles in its function, preservation, and regulation is being increasingly investigated. In the present study we focused on the impact of TFAM on the relation between the oxidative injury induced by the addition of glucocorticoid to a hypoxic environment and osteocytic cell necrosis. Using cultured osteocytes MLO-Y4 in a 1% hypoxic environment (hypoxia) to which 1µM dexamethasone (Dex) was added (Dex(+)/hypoxia(+)), an immunocytochemical study was conducted using 8-hydroxy-2'-deoxyguanosine (8-OHdG), an index of oxidative stress, and hypoxia inducible factor-1α (HIF-1α), a marker of hypoxia. Next, after adding TFAM siRNA, TFAM knockdown, cultured for 24h, and mitochondrial membrane potential were measured, they were stained with ATP5A which labels adenosine triphosphate (ATP) production. Dex was added to MLO-Y4 to which TFAM had been added, and cultured for 24h in hypoxia. The ratio of dead cells to viable cells was determined and compared. Enhanced expression of 8-OHdG, HIF-1α was found in osteocytes following the addition of glucocorticoid in a hypoxic environment. With TFAM knockdown, as compared to normoxia, mitochondrial function significantly decreased. On the other hand, by adding TFAM, the incidence of osteocytic cell necrosis was significantly decreased as compared with Dex(+)/hypoxia(+). TFAM was confirmed to be important in mitochondrial function and preservation, inhibition of oxidative injury and maintenance of ATP production. Moreover, prevention of mitochondrial injury can best be achieved by decreasing the development of osteocytic cell necrosis.

Cyclooxygenase-2-Mediated Up-Regulation of Mitochondrial Transcription Factor A Mitigates the Radio-Sensitivity of Cancer Cells

Mitochondrial transcription factor A (TFAM) regulates mitochondrial biogenesis, and it is a candidate target for sensitizing tumor during therapy. Previous studies identified that increased TFAM expression conferred tumor cells resistance to ionizing radiation. However, the mechanisms on how TFAM are regulated in irradiated tumor cells remain to be explored. In this research, we demonstrated the contribution of cyclooxygenase-2 (COX-2) to enhancing TFAM expression in irradiated tumor cells. Our results showed TFAM was concomitantly up-regulated with COX-2 in irradiated tumor cells. Inhibition of COX-2 by NS-398 blocked radiation-induced expression of TFAM, and prostaglandin E2 (PGE2) treatment stimulated TFAM expression. We next provided evidence that DRP1-mediated mitochondrial fragmentation was a reason for TFAM up-regulation in irradiated cells, by using small interfering RNA (siRNA) and selective inhibitor-targeted DRP1. Furthermore, we proved that p38-MAPK-connected COX-2, and DRP1-mediated TFAM up-regulation. Enhanced phosphorylation of p38 in irradiated tumor cells promoted DRP1 expression, mitochondrial fragmentation, and TFAM expression. NS-398 treatment inhibited radiation-induced p38 phosphorylation, while PGE2 stimulated the activation of p38. The results put forward a mechanism where COX-2 stimulates TFAM expression via p38-mediated DRP1/mitochondrial fragmentation signaling in irradiated tumor cells, which may be of value in understanding how to sensitize cancer cells during radiotherapy.