Sirtuins mediate mitochondrial quality control mechanisms: a novel therapeutic target for osteoporosis

METTL14 promotes TBK1 mRNA stability through IGF2BP3-recognized m6A modification and enhances mitophagy in BMSCs

Osteoporosis, particularly postmenopausal osteoporosis, represents a growing global health challenge characterized by impaired bone remodeling and increased fracture risk. The impairment of bone regeneration manifests in the field of oral and maxillofacial medicine as delayed alveolar bone healing after tooth extraction and poor osseointegration of dental implants, significantly compromising oral functional rehabilitation. This study investigates the role of METTL14 in osteogenic differentiation and its potential regulatory mechanisms in bone metabolism. We identified differential expression patterns of METTL14 in bone marrow-derived mesenchymal stem cells (BMSCs) between osteoporotic patients and healthy controls. Through loss-of-function experiments, we further demonstrated the critical role of METTL14 in promoting osteogenic differentiation, providing direct evidence for its functional importance in bone metabolism regulation. Transcriptome sequencing analysis revealed a significant association between METTL14 and mitophagy. JC-1 assay, Mitosox assay, mt-Keima assay, western blotting and immunofluorescence demonstrated METTL14's positive regulatory role in mitophagy, with TBK1 identified as the most significantly altered downstream target through qRT-PCR and rescue experiments. We further elucidated that IGF2BP3, an m6A reader, promotes osteogenesis and regulates TBK1 mRNA stability, as evidenced by Actinomycin D treatment and mitochondrial-lysosomal colocalization assays. In vivo experiments showed that METTL14 overexpression enhanced alveolar bone healing in ovariectomized osteoporotic mice. These findings provide novel evidence supporting METTL14 as a potential therapeutic target for osteoporosis.

SIRT1 Alleviates Oxidative Stress-Induced Mitochondrial Dysfunction and Mitochondria-Associated Membrane Dysregulation in Stress Urinary Incontinence

The pathogenesis of stress urinary incontinence (SUI), a condition common in women, remains to be fully elucidated. This study revealed that the incidence of SUI is associated with mitochondrial homeostasis dysregulation following oxidative stress in the fibrous connective tissue of the pelvic floor. SIRT1 is an essential factor for maintaining mitochondrial homeostasis; however, its potential role and mechanism of action in SUI pathogenesis remain unclear. Both in vitro and in vivo, we observed that oxidative stress reduced SIRT1 expression to inhibit the PGC-1α/NRF1/TFAM and PINK1/Parkin signalling pathways, eliciting impairment of mitochondrial biogenesis and mitophagy in L929 cells and SUI mice. Decreased SIRT1 levels induced endoplasmic reticulum (ER) stress and altered the structure of mitochondria-associated membranes (MAMs), disrupting ER-mitochondrial calcium homeostasis and exacerbting ROS accumulation. SIRT1 activation can restore mitochondrial function and the structure of MAMs and alleviate ER stress in fibroblasts, promoting anterior vaginal wall repair and improving urodynamic parameters in the SUI model. Our findings provide novel insights into the role and associated mechanism of SIRT1 in ameliorating oxidative stress-induced mitochondrial dysfunction in fibroblasts of the anterior vaginal wall and propose SIRT1 as a potential therapeutic target for SUI.

SIRT5 -mediated desuccinylation of UQCRC2 attenuates osteogenic differentiation of aged BM-MSCs through impairing mitochondrial homeostasis

BACKGROUND

The osteogenic differentiation potential of bone marrow mesenchymal stem cells (BM-MSCs) is critical for bone regeneration and repair. In recent years, the role of protein succinylation modification in regulating cellular metabolism has garnered increasing attention. However, its mechanism in osteogenic differentiation remains unclear.

METHODS

Oxygen consumption rate (OCR) and mitochondrial ROS (mtROS) were detected to assess mitochondrial function in BM-MSCs with successive passages. Alizarin red staining and western blot experiments were used to evaluate osteogenic differentiation capacity. Succinylation modification omics and Co-IP detection were conducted to determine SIRT5-mediated desuccinylation of UQCRC2.

RESULTS

Bioinformatics analysis revealed that sirtuin 5 (SIRT5) expression is upregulated with multiple rounds of BM-MSCs' passages, and is associated with biological pathways such as oxidative phosphorylation (OXPHOS), cellular senescence, and inhibition of osteogenic differentiation. Experiments in vitro confirmed the up-regulation of SIRT5 and the suppression of osteogenic differentiation with the increased times of BM-MSCs' passages. Overexpression of SIRT5 enhanced OXPHOS and elevated mtROS levels, but reduced the expression of Runx2 and osteocalcin, and decreased calcified nodules, thereby inhibiting the osteogenic differentiation of BM-MSCs. SIRT5-mediated desuccinylation of ubiquinol-cytochrome C reductase core protein 2 (UQCRC2) at the site of K250 promoted UQCRC2 translocation from cytoplasm to mitochondria, which enhanced the activity of mitochondrial respiratory complex III. It further increased mtROS, accelerated cellular senescence and inhibited the osteogenic differentiation of BM-MSCs.

CONCLUSION

SIRT5 reduces succinylation modification of UQCRC2, promotes mitochondrial respiration and mtROS, and thus reduces the osteogenic differentiation ability of BM-MSCs cells. SIRT5 might be a potential target to prevent the suppression of osteogenic differentiation of of BM-MSCs after multiple rounds passages.

Alda-1 mediates cell senescence and counteracts bone loss in weightlessness through regulating mitophagy

AIMS

Astronauts experience weightlessness-induced bone loss (WIBL) due to an imbalanced bone remodeling process involving bone mesenchymal stem cells (BMSCs), osteoblasts, and osteoclasts. Senescence is an important factor contributes to WIBL. In the current study, the effects of Alda-1 on senescence and WIBL were evaluated.

MATERIALS AND METHODS

We used the 2D-Rotating Wall Vessel bioreactor and hindlimb suspension rats, the classic cellular and animal models simulating microgravity (SMG). Aging, osteogenic differentiation, osteoclastic differentiation, and lipogenic differentiation were evaluated in the cell and animal models. Differentially expressed proteins in the femurs of rats were further analyzed using bioinformatics analysis. In addition, mitochondrial membrane potential, reactive oxygen species (ROS) production, and mitophagy markers were identified to estimate mitochondrial activity.

KEY FINDINGS

It was revealed that SMG accelerated senescence including osteoblasts, BMSCs, and inhibited senescence of RAW264.7 cells. SMG suppressed osteogenesis while promoting osteoclastogenesis and adipogenesis during cell senescence and bone loss. Aldehyde dehydrogenase-2 (ALDH2) was negatively related to WIBL. It was mainly enriched in mitochondria and involved in oxidative stress pathways. Finally, it was proved that Alda-1 significantly promoted ALDH2 levels. Alda-1 exhibited a robust protective response against senescence and WIBL by eliminating ROS accumulation, restoring mitophagy, and protecting cells and bone from apoptosis.

SIGNIFICANCE

Our study indicate that Alda-1 exerts a protective effect against SMG-induced skeletal aging and bone loss through mitophagy. It provides a theoretical basis for advancing therapeutic options against WIBL in space.

The Sirt1/FOXO signal pathway involves in regulating osteomyelitis progression via modulating mitochondrial dysfunctions and osteogenic differentiation

The Sirtuin-1 (Sirt1) gene has been reported to be closely associated with the progression of multiple diseases, but its role in regulating osteomyelitis (OM) pathogenesis has not been explored. The murine long bone-derived osteocyte-like MLO-Y4 cells and osteoblast-like MC3T3-E1 cells were exposed to Staphylococcal protein A (SpA) treatment to establish the in vitro OM models. The expression levels of Osteoblast-specific genes (OCN, OPN and RUNX2), osteoclastic genes (CTSK, MMP9 and ACP5) and the FOXO pathway-related proteins (FOXO1, p-FOXO1, FOXO3 and p-FOXO3) were detected by performing Real-Time qPCR and Western Blot analysis. Osteoblastic differentiation of the cells were evaluated by using the alizarin red S staining assay and TRAP staining assay, and membrane potential and superoxide production were measured to evaluate the mitochondrial functions of the cells. SpA treatment significantly suppressed osteogenic differentiation and induced mitochondrial dysfunction in MLO-Y4 and MC3T3-E1 cells, and promoting osteoclastogenesis in RAW264.7 cells, suggesting that the in vitro OM models were successfully established. Of note, SpA decreased the expression levels of Sirt1 in the OM cells, and SpA-induced detrimental effects on the OM cells were all reversed by overexpressing Sirt1. Mechanistically, Sirt1-overexpression increased the levels of phosphorylated FOXO-related proteins (p-FOXO1 and p-FOXO3) to activate the FOXO signal pathway and ameliorated OM progression in SpA-treated cells. Collectively, it was revealed in the present study that overexpression of Sirt1 activated the FOXO signal pathway to ameliorate SpA-induced detrimental effects in the OM cells, and Sirt1 could be potentially used as therapeutic agent for OM in clinic.

Exosomal non-coding RNAs in the regulation of bone metabolism homeostasis: Molecular mechanism and therapeutic potential

Bone metabolism is a dynamic balance between bone formation and absorption regulated by osteoblasts/osteoclasts. Bone metabolic disorders can lead to metabolic bone disease. Osteoporosis (OP), osteoarthritis (OA) and femoral head necrosis (ONFH) are common metabolic bone diseases. At present, the treatment of metabolic bone disease is still mainly to relieve pain and improve joint function. However, surgical treatment does not apply to the vast majority of high-risk groups, including postmenopausal women, patients with diabetes, cirrhosis, etc. Exosomes (Exos) are nanoscale membrane vesicles that are released by almost all cells. Exos are rich in a variety of bioactive substances, such as non-coding RNAs, nucleic acids, proteins and lipids. In view of the structure of Exos, it can protect the biologically active molecules can be smoothly delivered to the target cells and involved in the regulation of cell function. In this review, we focus on the regulation mechanism and function of bone homeostasis mediated by exosomal ncRNAs (Exos-ncRNAs), including macrophage polarization, autophagy, angiogenesis, signal transduction and competing endogenous RNA (ceRNA). We summarized the therapeutic strategies and potential drugs of Exos-ncRNAs in metabolic bone disease. Moreover, we discussed the shortcomings and potential research directions of Exos as carrier to deliver ncRNAs to play a role.

Phase 1, Single-Center, Double-Blind, Randomized, Placebo-Controlled Studies of the Safety, Tolerability, and Pharmacokinetics of Single and Multiple Ascending Oral Doses of the Sirtuin 6 Activator SP-624 in Healthy Adults

Sirtuin 6 activation is a novel epigenetic mechanism proposed for treatment of depression. Two Phase 1 studies, SP-624-101 and SP-624-102, examined the pharmacokinetics and safety of SP-624, an orally active sirtuin 6 activator, in healthy adults. SP-624-101 was a single-ascending-dose study. In Part A, participants were randomized 6:2 to SP-624 (single oral doses of 3, 10, or 30 mg) or placebo. Part B compared results in 8 participants receiving SP-624 while fasting or after a high-fat, high-calorie breakfast. In SP-624-102, a multiple-ascending-dose study, participants were randomized 6:2 to SP-624 (3 or 10 mg SP-624 daily) or placebo for 5 days and 5:2 to SP-624 20 mg daily or placebo for 10 days. At all doses, maximum concentration (Cmax) exceeded predicted target plasma concentrations of 3.28 ng/mL. Area under the concentration-time curve and Cmax increased dose proportionally. A food effect resulted in significantly lower Cmax, later time to maximum concentration, and comparable AUC for fed versus fasting participants. No serious adverse events were observed. In SP-624-101 and SP-624-102, respectively, 3 (12%) and 5 (29%) SP-624-treated participants experienced treatment-emergent adverse events. SP-624 was well tolerated and reached target concentrations in healthy adults, supporting progression of SP-624 20 mg daily into Phase 2 studies of major depressive disorder.

Important Role of Mitochondrial Dysfunction in Immune Triggering and Inflammatory Response in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease, primarily characterized by chronic symmetric synovial inflammation and erosive bone destruction.Mitochondria, the primary site of cellular energy production, play a crucial role in energy metabolism and possess homeostatic regulation capabilities. Mitochondrial function influences the differentiation, activation, and survival of both immune and non-immune cells involved in RA pathogenesis. If the organism experiences hypoxia, genetic predisposition, and oxidative stress, it leads to mitochondrial dysfunction, which further affects immune cell energy metabolism, synovial cell proliferation, apoptosis, and inflammatory signaling, causing the onset and progression of RA; and, mitochondrial regulation is becoming increasingly important in the treatment of RA.In this review, we examine the structure and function of mitochondria, analyze the potential causes of mitochondrial dysfunction in RA, and focus on the mechanisms by which mitochondrial dysfunction triggers chronic inflammation and immune disorders in RA. We also explore the effects of mitochondrial dysfunction on RA immune cells and osteoblasts, emphasizing its key role in the immune response and inflammatory processes in RA. Furthermore, we discuss potential biological processes that regulate mitochondrial homeostasis, which are of great importance for the prevention and treatment of RA.

Role of the PGAM5-CypD mitochondrial pathway in methylglyoxal-induced bone loss in diabetic osteoporosis

Diabetic osteoporosis (DOP) is a skeletal complication with a high rate of disability. It results in a great burden to the patient's family and society. Methylglyoxal (MG) is a toxic by-product of the glycolytic process that occurs during diabetic conditions. It causes osteoblastic injury and con-tributes to the initiation and development of DOP. Disruption of mitochondrial homeostasis has been implicated as a cause of dysregulated osteo-blastogenesis, an essential step in bone formation. It is unclear whether mitochondrial dysfunction is involved in MG-induced osteoblast dysfunction. In this study, we showed that mitochondrial dysfunction contributes to MG-induced MC3T3-E1 cell apoptosis and impaired differentiation. A significant reduction of mitochondrial membrane potential (MMP) and ATP production occurred in MG-induced osteoblasts as well as increasing mitochondrial reactive oxygen species (mtROS) and intracellular Ca2+. Classical antioxidant N-Acetylcysteine (NAC) significantly attenuated mitochondrial dysfunction as well as osteoblast apoptosis and osteogenic differentiation damage induced by MG. More importantly, we found that activating phosphoglycerate mutase family member 5 (PGAM5) and cyclophilin D (CypD), which contributes to mitochondrial homeostasis, is involved in MG-induced osteoblast injury. Both PGAM5 and CypD knockdown effectively reversed osteoblast viability and function, whereas PGAM5 or CypD overexpression aggravated osteoblast injury caused by MG. Moreover, the result of co-transfection revealed that PGAM5 is an upstream signaling molecule of CypD. By constructing type I diabetes mouse models, we further found that the expression of PGAM5 and CypD were both increased in the femur along with a reduction of ATP and increased TUNEL-positive cells. These results, for the first time, suggest that MG-induced mitochondrial dysfunction induces osteoblast injury through the PGAM5-CypD pathway. This study provides insight into the prevention and treatment of DOP. LAY SUMMARY: This study highlights the role of mitochondria in regulating osteoblast viability and function under conditions of diabetic osteoporosis (DOP). We found that the PGAM5-CypD mitochondrial pathway is activated following glycolytic by-product methylglyoxal (MG) treatment, which contributes to mitochondrial dysfunction and osteogenic dysfunction. This mechanism implicates mitochondria as a potential therapeutic target for osteoporosis.

The interplay between osteoarthritis and osteoporosis: Mechanisms, implications, and treatment considerations - A narrative review

This comprehensive review examines the relationship between osteoarthritis (OA) and osteoporosis (OP), two common disorders in the elderly. OA involves joint cartilage degeneration and pain, while OP leads to fractures due to reduced bone mass. Despite different pathologies, both conditions share risk factors such as age and genetics. Studies reveal mixed results: some show higher bone mineral density (BMD) in OA patients, suggesting an inverse relationship, while others find no significant link. Proposed mechanisms include mechanical loading, bone remodeling, and inflammation. Clinical strategies focus on maintaining bone health in OA and monitoring joint health in OP, with treatments like bisphosphonates and exercise. Understanding these interactions is crucial for developing integrated treatments to improve patient outcomes and quality of life. Further research is needed to clarify these complex mechanisms.

The Role of Mitochondrial Homeostasis in Mesenchymal Stem Cell Therapy-Potential Implications in the Treatment of Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a hereditary disorder characterized by bones that are fragile and prone to breaking. The efficacy of existing therapies for OI is limited, and they are associated with potentially harmful side effects. OI is primarily due to a mutation of collagen type I and hence impairs bone regeneration. Mesenchymal stem cell (MSC) therapy is an attractive strategy to take advantage of the potential benefits of these multipotent stem cells to address the underlying molecular defects of OI by differentiating osteoblasts, paracrine effects, or immunomodulation. The maintenance of mitochondrial homeostasis is an essential component for improving the curative efficacy of MSCs in OI by affecting the differentiation, signaling, and immunomodulatory functions of MSCs. In this review, we highlight the MSC-based therapy pathway in OI and introduce the MSC regulation mechanism by mitochondrial homeostasis. Strategies aiming to modulate the metabolism and reduce the oxidative stress, as well as innovative strategies based on the use of compounds (resveratrol, NAD+, α-KG), antioxidants, and nanomaterials, are analyzed. These findings may enable the development of new strategies for the treatment of OI, ultimately resulting in improved patient outcomes.

Research advances on silence information regulator 6 as a potential therapeutic target for bone regeneration and repair

Segmental bone defects and nonunion of fractures caused by trauma, infection, tumor or systemic diseases with limited osteogenesis and prolonged bone healing cycles are challenging issues in orthopedic clinical practice. Therefore, identifying regulatory factors for bone tissue regeneration and metabolism is crucial for accelerating bone repair and reconstructing defective areas. Silence information regulator 6 (SIRT6), functioning as a deacetylase and nucleotide transferase, is extensively involved in the regulation of differentiation, apoptosis, metabolism, and inflammation in bone cells including osteoblasts and osteoclasts, and is considered to be an important factor in regulating bone metabolism. SIRT6 forms a complex with B lymphocyte-induced maturation protein 1 (Blimp1), down-regulates the expression of the nuclear factor κB (NF-κB) pathway, and promotes the expression of the ERα-FasL axis signal to inhibit osteoclast formation and maturation differentiation, thereby hindering bone resorption and increasing bone mass. In addition, SIRT6 activates the Akt-mTOR pathway to regulate the autophagy level and osteogenesis of bone marrow mesenchymal stem cells, inhibits glycolysis and reactive oxygen production in osteoblasts, promotes osteoblast differentiation through the CREB/CCN1/COX2 pathway and the bone morphogenetic protein (BMP) signaling pathway, enhances bone formation, and accelerates bone regeneration and repair of skeletal tissue. This article provides an overview of the research progress on SIRT6 in the pathophysiology of bone regeneration, revealing its potential as a novel therapeutic target for bone tissue repair to alleviate the progression of skeletal pathological diseases.

Mitochondria: a breakthrough in combating rheumatoid arthritis

As a chronic autoimmune disease with complex aetiology, rheumatoid arthritis (RA) has been demonstrated to be associated with mitochondrial dysfunction since mitochondrial dysfunction can affect the survival, activation, and differentiation of immune and non-immune cells involved in the pathogenesis of RA. Nevertheless, the mechanism behind mitochondrial dysfunction in RA remains uncertain. Accordingly, this review addresses the possible role and mechanisms of mitochondrial dysfunction in RA and discusses the potential and challenges of mitochondria as a potential therapeutic strategy for RA, thereby providing a breakthrough point in the prevention and treatment of RA.