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

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.

Plasma 8-OHdG act as a biomarker for steroid-induced osteonecrosis of the femoral head

BACKGROUND

Oxidative stress was closely related to the occurrence and development of Steroid-induced osteonecrosis of the femoral head (SIONFH). 8-hydroxy-2'-deoxyguanosine (8-OHdG) is a important index of oxidative stress. The aim of this study is to investigate the role of 8-OHdG in the development of SIONFH.

METHODS

From May 2021 and November 2021, 33 patients diagnosed with SIONFH and 26 healthy controls were recruited in this study. Assessment included the radiography and pathology evaluation of clinical bone tissue, expression position and level of 8-OHdG, level of plasma 8-OHdG, as well as the receiver operating characteristic (ROC) curve.

RESULTS

We observed that expression levels of 8-OHdG in bone samples decreased with Association Research Circulation Osseous (ARCO) stages. Plasma 8-OHdG levels were significantly increased in the SIONFH group compared to the healthy control group. Plasma 8-OHdG level of pre-collapse patients was higher than that of post-collapse patients, the decreased plasma 8-OHdG level was related to higher ARCO stages.

CONCLUSION

Plasma 8-OHdG may represent potential biomarkers during SIONFH at different stages. Higher plasma 8-OHdG levels indicated early stage of SIONFH. The current study provided new clues for early diagnosis and treatment for SIONFH.

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.

Systemic inflammatory response syndrome is triggered by mitochondrial damage (Review)

Mitochondria are key organelles of cellular energy metabolism; both mitochondrial function and metabolism determine the physiological function of cells and serve an essential role in immune responses. Key damage-associated molecular patterns (DAMPs), such as mitochondrial DNA and N-formyl peptides, released following severe trauma-induced mitochondrial damage may affect the respiratory chain, enhance oxidative stress and activate systemic inflammatory responses via a variety of inflammation-associated signaling pathways. Severe trauma can lead to sepsis, multiple organ dysfunction syndrome and death. The present review aimed to summarize the pathophysiological mechanisms underlying the effects of human mitochondrial injury-released DAMPs on triggering systemic inflammatory responses and to determine their potential future clinical applications in preventing and treating sepsis.

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.

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.