Activation of AMPK-SIRT3 signaling is chondroprotective by preserving mitochondrial DNA integrity and function

Yanghe decoction alleviates osteoarthritis by AMPK-SIRT3 positive feedback loop-mediated mitochondrial autophagy

ETHNOPHARMACOLOGICAL RELEVANCE

Yanghe Decoction(YHD) is a traditional Chinese medicine compound known for its efficacy in treating osteoarthritis (OA).

AIM OF THE STUDY

We aimed to explore the underlying mechanisms of YHD in relation to OA.

MATERIALS AND METHODS

UHPLC-MS technology was used to identify the material basis of YHD. In vivo, OA rat model was induced by the modified Hulth method and then treated with YHD at three different doses (0.625, 1.3 and 2.6 g/kg/d). In vitro,YHD-Contained serum was prepared and administrated into rat chondrocytes, followed by simulation of Lipopolysaccharide(LPS). The protective mechanism was determined by observation of morphology, Flow cytometry and Protein level detection.

RESULTS

In vivo, YHD reduced chondrocyte apoptosis and joint inflammation while promoting mitophagy. It also elevated the protein levels of p-AMPK, SIRT3, PINK1, Parkin, and LC3II/I. In vitro, YHD-Contained Serum reduced chondrocyte apoptosis, decreased mitochondrial ROS, enhanced mitochondrial membrane potential, and upregulated the protein expressions of p-AMPK, SIRT3, PINK1, Parkin, and LC3II/I.

CONCLUSION

Through this study, we demonstrated YHD protect chondrocytes against apoptosis, and its underlying mechanisms may involve the regulation of AMPK-SIRT3 positive feedback loop and activation of PINK1/Parkin mediated mitophagy.

GATD3A-deficiency-induced mitochondrial dysfunction facilitates senescence of fibroblast-like synoviocytes and osteoarthritis progression

Accumulating evidence indicates that cellular senescence is closely associated with osteoarthritis. However, there is limited research on the mechanisms underlying fibroblast-like synoviocyte senescence and its impact on osteoarthritis progression. Here, we elucidate a positive correlation between fibroblast-like synoviocyte senescence and osteoarthritis progression and reveal that GATD3A deficiency induces fibroblast-like synoviocyte senescence. Mechanistically, GATD3A deficiency enhances the binding of Sirt3 to MDH2, leading to deacetylation and decreased activity of MDH2. Reduced MDH2 activity impairs tricarboxylic acid cycle flux, resulting in mitochondrial dysfunction and fibroblast-like synoviocyte senescence. Intra-articular injection of recombinant adeno-associated virus carrying GATD3A significantly alleviates the osteoarthritis phenotype in male mice. This study increases our current understanding of GATD3A function. In particular, we reveal a novel mechanism of fibroblast-like synoviocyte senescence, suggesting that targeting GATD3A is a potential therapeutic approach for osteoarthritis.

7-Hydroxy-3-(4'-methoxyphenyl) coumarin (C12) attenuates bleomycin-induced acute lung injury and fibrosis through activation of SIRT3

Silent mating-type information regulation 2 homology 3 (SIRT3) is a member of the sirtuins family expressed in mitochondria performs deacetylation of metabolic enzymes and promotes longevity. 7-hydroxy-3-(4'-methoxyphenyl) coumarin (C12) is a small molecule first ever known for its direct activation of SIRT3. SIRT3 performs its function by balancing the redox system by activating manganese superoxide dismutase (MnSOD) and 8-Oxoguanine glycosylase (OGG1). For the first time, we reported that activation of SIRT3 by C12 attenuated bleomycin (BLM)-)-induced acute lung injury and pulmonary fibrosis. C12 prevented the oxidative stress and injury caused by BLM in alveolar epithelial cells (BEAS-2B) in in vitro and inhibited the fibrosis in transforming growth factor-beta (TGF-β) induced fibrosis in fibroblasts (MRC-5). Additionally, activation of SIRT3 by C12 in vivo mice model alleviated BLM-induced inflammation, collagen accumulation, cellular infiltration, and restoration of alveolar architecture by inhibiting TGF-β, smooth muscle actin (α-SMA), collagen-1A, collagen-3A, and mesenchymal markers. The protective effect of C12 was through activation of MnSOD and OGG1 in both in vitro and in vivo models suggesting C12 can be a potent SIRT3 activator and helps to treat fibrotic-related diseases.

IKKα affects the susceptibility of primary human osteoarthritis chondrocytes to oxidative stress-induced DNA damage by tuning autophagy

The functional derangement affecting human chondrocytes during osteoarthritis (OA) onset and progression is sustained by the failure of major homeostatic mechanisms. This makes them more susceptible to oxidative stress (OS), which can induce DNA damage responses and exacerbate stress-induced senescence. The knockdown (KD) of IκB kinase α (IKKα), a dispensable protein in healthy articular cartilage physiology, was shown to increase the survival and replication potential of human primary OA chondrocytes. Our recent findings showed that the DNA Mismatch Repair pathway only partially accounts for the reduced susceptibility to OS of IKKαKD cells. Here we therefore investigated other ROS-mediated DNA damage and repair mechanisms. We exposed IKKαWT and IKKαKD chondrocytes to sub-cytotoxic hydrogen peroxide and evaluated the occurrence of double-strand breaks (DSB), 8-oxo-2'-deoxyguanosine (8-oxo-dG) and telomere shortening. ROS exposure was able to significantly increase the number of γH2AX foci (directly related to the number of DSB) in both cell types, but IKKα deficient cells undergoing cell division were able to better recover compared to their IKKα proficient counterpart. 8-oxo-dG signal proved to be the highest DNA damage signal among those investigated, located in the mitochondria and with a slightly higher intensity in IKKα proficient cells immediately after OS exposure. Furthermore, ROS significantly reduced telomere length both in IKKαWT and IKKαKD, with the former showing more pervasive effects, especially in dividing cells. Assessment of the HIF-1α>Beclin-1>LC3B axis after recovery from OS showed that IKKα deficient cells exhibited a more efficient autophagic machinery that allowed them to better cope with oxidative stress, possibly through the turnover of damaged mitochondria. Higher Beclin-1 levels likely helped in rescuing dividing cells (identified by coupled cell cycle analysis) because of Beclin-1's involvement in both autophagy and mitotic spindle organization. Therefore, our data further confirm the higher capacity of IKKαKD chondrocytes to cope with oxidative stress-induced DNA damage.

OGG1: An emerging multifunctional therapeutic target for the treatment of diseases caused by oxidative DNA damage

Oxidative DNA damage-related diseases, such as incurable inflammation, malignant tumors, and age-related disorders, present significant challenges in modern medicine due to their complex molecular mechanisms and limitations in identifying effective treatment targets. Recently, 8-oxoguanine DNA glycosylase 1 (OGG1) has emerged as a promising multifunctional therapeutic target for the treatment of these challenging diseases. In this review, we systematically summarize the multiple functions and mechanisms of OGG1, including pro-inflammatory, tumorigenic, and aging regulatory mechanisms. We also highlight the potential of OGG1 inhibitors and activators as potent therapeutic agents for the aforementioned life-limiting diseases. We conclude that OGG1 serves as a multifunctional hub; the inhibition of OGG1 may provide a novel approach for preventing and treating inflammation and cancer, and the activation of OGG1 could be a strategy for preventing age-related disorders. Furthermore, we provide an extensive overview of successful applications of OGG1 regulation in treating inflammatory, cancerous, and aging-related diseases. Finally, we discuss the current challenges and future directions of OGG1 as an emerging multifunctional therapeutic marker for the aforementioned challenging diseases. The aim of this review is to provide a robust reference for scientific researchers and clinical drug developers in the development of novel clinical targeted drugs for life-limiting diseases, especially for incurable inflammation, malignant tumors, and age-related disorders.

Antioxidant hydrogels for the treatment of osteoarthritis: mechanisms and recent advances

Articular cartilage has limited self-healing ability, resulting in injuries often evolving into osteoarthritis (OA), which poses a significant challenge in the medical field. Although some treatments exist to reduce pain and damage, there is a lack of effective means to promote cartilage regeneration. Reactive Oxygen Species (ROS) have been found to increase significantly in the OA micro-environment. They play a key role in biological systems by participating in cell signaling and maintaining cellular homeostasis. Abnormal ROS expression, caused by internal and external stimuli and tissue damage, leads to elevated levels of oxidative stress, inflammatory responses, cell damage, and impaired tissue repair. To prevent excessive ROS accumulation at injury sites, biological materials can be engineered to respond to the damaged microenvironment, release active components in an orderly manner, regulate ROS levels, reduce oxidative stress, and promote tissue regeneration. Hydrogels have garnered significant attention due to their excellent biocompatibility, tunable physicochemical properties, and drug delivery capabilities. Numerous antioxidant hydrogels have been developed and proven effective in alleviating oxidative stress. This paper discusses a comprehensive treatment strategy that combines antioxidant hydrogels with existing treatments for OA and explores the potential applications of antioxidant hydrogels in cartilage tissue engineering.

Bioenergetic-active exosomes for cartilage regeneration and homeostasis maintenance

Cartilage regeneration relies on adequate and continuous bioenergy supply to facilitate cellular differentiation and extracellular matrix synthesis. Chondrocytes frequently undergo energy stress under pathological conditions, characterized by disrupted cellular metabolism and reduced adenosine triphosphate (ATP) levels. However, there has limited progress in modulating energy metabolism for cartilage regeneration thus far. Here, we developed bioenergetic-active exosomes (Suc-EXO) to promote cartilage regeneration and homeostasis maintenance. Suc-EXO exhibited a 5.42-fold increase in ATP content, enabling the manipulation of cellular energy metabolism by fueling the TCA cycle. With continuous energy supply, Suc-EXO promoted BMSC chondrogenic differentiation via the P2X7-mediated PI3K-AKT pathway. Moreover, Suc-EXO improved chondrocyte anabolism and mitochondrial homeostasis via the P2X7-mediated SIRT3 pathway. In a rabbit cartilage defect model, the Suc-EXO-encapsulated hydrogel notably promoted cartilage regeneration and maintained neocartilage homeostasis, leading to 2.26 and 1.53 times increase in Col2 and ACAN abundance, respectively. These findings make a remarkable breakthrough in modulating energy metabolism for cartilage regeneration, offering immense potential for clinical translation.

Therapeutic upregulation of DNA repair pathways: strategies and small molecule activators

DNA repair activity diminishes with age and genetic mutations, leading to a significantly increased risk of cancer and other diseases. Upregulating the DNA repair system has emerged as a potential strategy to mitigate disease susceptibility while minimizing cytotoxic side effects. However, enhancing DNA repair activity presents significant challenges due to the inherent inefficiency in activator screening processes. Additionally, pinpointing a critical target that can effectively upregulate overall repair processes is complicated as the available information is somewhat sporadic. In this review, we discuss potential therapeutic targets for upregulating DNA repair pathways, along with the chemical structures and properties of reported small-molecule activators. We also elaborate on the diverse mechanisms by which these targets modulate repair activity, highlighting the critical need for a comprehensive understanding to guide the development of more effective therapeutic strategies.

Exploring Sirtuins: New Frontiers in Managing Heart Failure with Preserved Ejection Fraction

With increasing research, the sirtuin (SIRT) protein family has become increasingly understood. Studies have demonstrated that SIRTs can aid in metabolism and affect various physiological processes, such as atherosclerosis, heart failure (HF), hypertension, type 2 diabetes, and other related disorders. Although the pathogenesis of HF with preserved ejection fraction (HFpEF) has not yet been clarified, SIRTs have a role in its development. Therefore, SIRTs may offer a fresh approach to the diagnosis, treatment, and prevention of HFpEF as a novel therapeutic intervention target.

Molecular crosstalk and putative mechanisms underlying mitochondrial quality control: The hidden link with methylmercury-induced cognitive impairment

Methylmercury (MeHg) is a neurotoxin associated with foetal neurodevelopmental and adult cognitive deficits. Neurons are highly dependent on the tricarboxylic acid cycle and oxidative phosphorylation to produce ATP and meet their high energy demands. Therefore, mitochondrial quality control (MQC) is critical for neuronal homeostasis. While existing studies have generated a wealth of data on the toxicity of MeHg, the complex cascades and molecular pathways governing the mitochondrial network remain to be elucidated. Here, 0.6, 1.2 and 2.4 mg/kg body weight of MeHg were administered intragastrically to pregnant Sprague Dawley rats to model maternal MeHg exposure. The results of the in vivo study revealed that MeHg-treated rats tended to perform more directionless repetitive strategies in the Morris Water Maze and fewer target-orientation strategies than control offspring. Moreover, pathological injury and synaptic toxicity were observed in the hippocampus. Transmission electron microscopy (TEM) demonstrated that the autophagosomes encapsulated damaged mitochondria, while showing a typical mitochondrial fission phenotype, which was supported by the activation of PINK1-dependent key regulators of mitophagy. Moreover, there was upregulation of DRP1 and FIS1. Additionally, MeHg compensation promoted mitochondrial biogenesis, as evidenced by the activation of the mitochondrial PGC1-α-NRF1-TFAM signalling pathway. Notably, SIRT3/AMPK was activated by MeHg, and the expression and activity of p-AMPK, p-LKB1 and SIRT3 were consistently coordinated. Collectively, these findings provide new insights into the potential molecular mechanisms regulating MeHg-induced cognitive deficits through SIRT3/AMPK MQC network coordination.

The role and intervention of mitochondrial metabolism in osteoarthritis

Osteoarthritis (OA), a prevalent degenerative joint disease, affects a substantial global population. Despite the elusive etiology of OA, recent investigations have implicated mitochondrial dysfunction as a significant factor in disease pathogenesis. Mitochondria, pivotal cellular organelles accountable for energy production, exert essential roles in cellular metabolism. Hence, mitochondrial dysfunction can exert broad-ranging effects on various cellular processes implicated in OA development. This comprehensive review aims to provide an overview of the metabolic alterations occurring in OA and elucidate the diverse mechanisms through which mitochondrial dysfunction can contribute to OA pathogenesis. These mechanisms encompass heightened oxidative stress and inflammation, perturbed chondrocyte metabolism, and compromised autophagy. Furthermore, this review will explore potential interventions targeting mitochondrial metabolism as means to impede or decelerate the progression of OA. In summary, this review offers a comprehensive understanding of the involvement of mitochondrial metabolism in OA and underscores prospective intervention strategies.

SIRT3 alleviates high glucose-induced chondrocyte injury through the promotion of autophagy and suppression of apoptosis in osteoarthritis progression

A growing amount of epidemiological evidence proposes diabetes mellitus (DM) to be an independent risk factor for osteoarthritis (OA). Sirtuin 3 (SIRT3), which is mainly located in mitochondria, belongs to the family of nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases and is involved in the physiological and pathological processes of cell regulation. The aim of this study was to investigate the effects of SIRT3 on diabetic OA and underlying mechanisms in the prevention of type 2 DM (T2DM)-induced articular cartilage damage. High-fat and high-sugar diets combined with streptozotocin (STZ) injection were used for establishing an experimental T2DM rat model. The destabilization of medial meniscus (DMM) surgery was applied to induce the rat OA model. Primary rat chondrocytes were cultivated with a concentration of gradient glucose. Treatment with intra-articular injection of SIRT3 overexpression lentivirus was achieved in vivo, and intervention with SIRT3 knockdown was performed using siRNA transfection in vitro. High glucose content was found to activate inflammatory response, facilitate apoptosis, downregulate autophagy, and exacerbate mitochondrial dysfunction in a dose-dependent manner in rat chondrocytes, which can be deteriorated by SIRT3 knockdown. In addition, articular cartilage damage was found to be more severe in T2DM-OA rats than in DMM-induced OA rats, which can be mitigated by the intra-articular injection of SIRT3 overexpression lentivirus. Targeting SIRT3 is a potential therapeutic strategy for the alleviation of diabetic OA.

Isolation of Calenduloside E from Achyranthes bidentata Blume and its effects on LPS/D-GalN-induced acute liver injury in mice by regulating the AMPK-SIRT3 signaling pathway

BACKGROUND

Acute liver injury (ALI) is a frequent fatal liver disease with a high mortality. Calenduloside E (CE) is a pentacyclic triterpenoid derived from Achyranthes bidentata Blume. It has been found that liver injury is associated with mitochondrial dysfunction, and activation of the AMPK-SIRT3 signaling pathway protects the mitochondrial function to play a role in resistance to the disease. However, whether CE is protective against ALI through the AMPK-SIRT3 signaling pathway is unclear.

PURPOSE

To clarify the influences of Calenduloside E (CE) isolated from Achyranthes bidentata Blume on LPS/D-GalN-induced Acute liver injury (ALI).

METHODS

A mouse model of ALI was developed, intraperitoneal injection of 10 μg/kg LPS and 700 mg/kg D-GalN, histopathological, oxidative stress, and immune inflammation of the mice were monitored. The mechanism of CE influencing liver injury was investigated by examining the gut microbiota, mitochondrial dysfunction, and the AMPK-SIRT3 signaling pathway. The antagonistic effects of specific AMPK and SIRT3 blocker, as well as AMPKα1, AMPKα2, SIRT3 transfection-mediated silencing were investigated to confirm the role of the AMPK-SIRT3 signaling pathway in this process.

RESULTS

CE relieved liver pathological damage of mice and led to reduced oxidative stress and immune inflammation in mice, affected the balance of gut microbiota in mice with liver injury, as well as energy metabolism, and regulated mRNA and protein expressions of AMPK-SIRT3 signaling pathway. In addition, in vitro studies showed that CE relieved mitochondrial respiratory and protein expressions of AMPK-SIRT3 signaling pathway in LPS/D-GalN-induced AML12 and LX2 cells, and such effect was blocked by AMPK and SIRT3 inhibitors. Furthermore, silencing of AMPKα1, AMPKα2, and SIRT3 blocked the effects of CE. Overall, the influences of CE on mice with liver injury is tuned by the AMPK-SIRT3 signaling pathway.

CONCLUSION

CE mediates mitochondrial function and eventually regulate energy metabolism by regulating the AMPK-SIRT3 signaling pathway. The results of this study provide molecular evidences for application of CE in treatment of ALI and provide references to the drug development for ALI.

AMPK role in epilepsy: a promising therapeutic target?

Epilepsy is a complex and multifaceted neurological disorder characterized by spontaneous and recurring seizures. It poses significant therapeutic challenges due to its diverse etiology and often-refractory nature. This comprehensive review highlights the pivotal role of AMP-activated protein kinase (AMPK), a key metabolic regulator involved in cellular energy homeostasis, which may be a promising therapeutic target for epilepsy. Current therapeutic strategies such as antiseizure medication (ASMs) can alleviate seizures (up to 70%). However, 30% of epileptic patients may develop refractory epilepsy. Due to the complicated nature of refractory epilepsy, other treatment options such as ketogenic dieting, adjunctive therapy, and in limited cases, surgical interventions are employed. These therapy options are only suitable for a select group of patients and have limitations of their own. Current treatment options for epilepsy need to be improved. Emerging evidence underscores a potential association between impaired AMPK functionality in the brain and the onset of epilepsy, prompting an in-depth examination of AMPK's influence on neural excitability and ion channel regulation, both critical factors implicated in epileptic seizures. AMPK activation through agents such as metformin has shown promising antiepileptic effects in various preclinical and clinical settings. These effects are primarily mediated through the inhibition of the mTOR signaling pathway, activation of the AMPK-PI3K-c-Jun pathway, and stimulation of the PGC-1α pathway. Despite the potential of AMPK-targeted therapies, several aspects warrant further exploration, including the detailed mechanisms of AMPK's role in different brain regions, the impact of AMPK under various conditional circumstances such as neural injury and zinc toxicity, the long-term safety and efficacy of chronic metformin use in epilepsy treatment, and the potential benefits of combination therapy involving AMPK activators. Moreover, the efficacy of AMPK activators in refractory epilepsy remains an open question. This review sets the stage for further research with the aim of enhancing our understanding of the role of AMPK in epilepsy, potentially leading to the development of more effective, AMPK-targeted therapeutic strategies for this challenging and debilitating disorder.

Osteoarthritis year in review 2023: Biology

Great progress continues to be made in our understanding of the multiple facets of osteoarthritis (OA) biology. Here, we review the major advances in this field and progress towards therapy development over the past year, highlighting a selection of relevant published literature from a PubMed search covering the year from the end of April 2022 to the end of April 2023. The selected articles have been arranged in themes. These include 1) molecular regulation of articular cartilage and implications for OA, 2) mechanisms of subchondral bone remodelling, 3) role of synovium and inflammation, 4) role of age-related changes including cartilage matrix stiffening, cellular senescence, mitochondrial dysfunction, metabolic dysfunction, and impaired autophagy, and 5) peripheral mechanisms of OA pain. Progress in the understanding of the cellular and molecular mechanisms responsible for the multiple aspects of OA biology is unravelling novel therapeutic targets for disease modification.

Erzhiwan Ameliorates Restraint Stress- and Monobenzone-Induced Depigmentation in Mice by Inhibiting Macrophage Migration Inhibitory Factor and 8-Hydroxy-2-Deoxyguanosine

Purpose

Vitiligo is an autoimmune disease that results in the loss of epidermal melanocytes. The treatments for patients with vitiligo remain lacking. Erzhiwan (EZW), a traditional Chinese Medicine composed of Ligustri Lucidi Fructus and Ecliptae Herba, was used to ameliorate depigmentation since ancient China. This study aims to investigate the effect of EZW on vitiligo-related depigmentation.

Methods

A vitiligo-related depigmentation mouse model was induced by monobenzone and restraint stress. The experimental depigmentation mice were treated with EZW. Histological observation of skin was conducted. Cutaneous oxidative damage and inflammation were determined. A network pharmacology analysis was carried out.

Results

EZW reduced depigmentation score (p<0.01), cutaneous inflammatory infiltration (p<0.01), and CD8α-positive expression (p<0.01), and increased cutaneous melanin content in experimental depigmentation mice. EZW reduced stress reaction in experimental depigmentation mice (p<0.01). EZW inhibited 8-hydroxy-2-deoxyguanosine (8-OHdG)-related DNA oxidative damage in the skin (p<0.05, p<0.01). In addition, EZW reduced cutaneous macrophage migration inhibitory factor (MIF)-CD74-NF-κB signaling (p<0.01). The network pharmacology analysis demonstrated that EZW regulated necroptosis, apoptosis, and FoxO signaling pathways in vitiligo. An in vitro experiment showed that the main ingredient of EZW, specnuezhenide, protected against monobenzone and MIF-induced cell death in HaCaT cells (p<0.01).

Conclusion

EZW ameliorates restraint stress- and monobenzone-induced depigmentation via the inhibition of MIF and 8-OHdG signaling. The findings provide a data basis of an utilization of EZW in vitiligo.

Sirtuins in macrophage immune metabolism: A novel target for cardiovascular disorders

Sirtuins (SIRT1-SIRT7), as a family of NAD+-dependent protein modifying enzymes, have various catalytic functions, such as deacetylases, dealkalylases, and deribonucleases. The Sirtuins family is directly or indirectly involved in pathophysiological processes such as glucolipid metabolism, oxidative stress, DNA repair and inflammatory response through various pathways and assumes an important role in several cardiovascular diseases such as atherosclerosis, myocardial infarction, hypertension and heart failure. A growing number of studies supports that metabolic and bioenergetic reprogramming directs the sequential process of inflammation. Failure of homeostatic restoration leads to many inflammatory diseases, and that macrophages are the central cells involving the inflammatory response and are the main source of inflammatory cytokines. Regulation of cellular metabolism has emerged as a fundamental process controlling macrophage function, but its exact signaling mechanisms remain to be revealed. Understanding the precise molecular basis of metabolic control of macrophage inflammatory processes may provide new approaches for targeting immune metabolism and inflammation. Here, we provide an update of studies in cardiovascular disease on the function and role of sirtuins in macrophage inflammation and metabolism, as well as drug candidates that may interfere with sirtuins, pointing to future prospects in this field.

Role of SIRT3 in bone homeostasis and its application in preventing and treating bone diseases

Bone homeostasis refers to the balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption and the maintenance of stable bone mass. SIRT3 is a class of mitochondrial protein deacetylase that influences various mitochondrial functions and is involved in the mechanisms underlying resistance to aging; regulation of bone marrow mesenchymal stem cells, osteoblasts, and osteoclasts; and development of osteoporosis, osteoarthritis, and other bone diseases. Moreover, exercise affects bones through SIRT3. Thus, studies on SIRT3 may provide insights for the treatment of bone diseases. Although SIRT3 can exert multiple effects on bone, the specific mechanism by which it regulates bone homeostasis remains unclear. By evaluating the relevant literature, this review discusses the structure and function of SIRT3, reveals the role and associated mechanisms of SIRT3 in regulating bone homeostasis and mediating bone health during exercise, and highlights the potential pharmacological value of SIRT3 in treating bone diseases.

Harnessing the multifunctionality of lipid-based drug delivery systems for the local treatment of osteoarthritis

Osteoarthritis (OA) is a widespread joint condition affecting millions globally, presenting a growing socioeconomic burden thus making the development of more effective therapeutic strategies crucial. This review emphasizes recent advancements in lipid-based drug delivery systems (DDSs) for intra-articular administration of OA therapeutics, encompassing non-steroidal anti-inflammatory drugs, corticosteroids, small molecule disease-modifying OA drugs, and RNA therapeutics. Liposomes, lipid nanoparticles, lipidic mesophases, extracellular vesicles and composite systems exhibit enhanced stability, targeted delivery, and extended joint retention, which contribute to improved therapeutic outcomes and minimized systemic drug exposure. Although active targeting strategies hold promise, further research is needed to assess their targeting efficiency in physiologically relevant conditions. Simultaneously, multifunctional DDSs capable of delivering combinations of distinct therapeutic classes offer synergistic effects and superior OA treatment outcomes. The development of such long-acting systems that resist rapid clearance from the joint space is crucial, where particle size and targeting capabilities emerge as vital factors. Additionally, combining cartilage lubrication properties with sustained drug delivery has demonstrated potential in animal models, meriting further investigation in human clinical trials. This review highlights the crucial need for direct, head-to-head comparisons of novel DDSs with standard treatments, particularly within the same drug class. These comparisons are essential in accurately evaluating their effectiveness, safety, and clinical applicability, and are set to significantly shape the future of OA therapy.

DMT1 differentially regulates mitochondrial complex activities to reduce glutathione loss and mitigate ferroptosis

Mitochondria are vital for energy production and redox homeostasis, yet knowledge of relevant mechanisms remains limited. Here, through a genome-wide CRISPR-Cas9 knockout screening, we have identified DMT1 as a major regulator of mitochondria membrane potential. Our findings demonstrate that DMT1 deficiency increases the activity of mitochondrial complex I and reduces that of complex III. Enhanced complex I activity leads to increased NAD+ production, which activates IDH2 by promoting its deacetylation via SIRT3. This results in higher levels of NADPH and GSH, which improve antioxidant capacity during Erastin-induced ferroptosis. Meanwhile, loss of complex III activity impairs mitochondrial biogenesis and promotes mitophagy, contributing to suppression of ferroptosis. Thus, DMT1 differentially regulates activities of mitochondrial complex I and III to cooperatly suppress Erastin-induced ferroptosis. Furthermore, NMN, an alternative method of increasing mitochondrial NAD+, exhibits similar protective effects against ferroptosis by boosting GSH in a manner similar to DMT1 deficiency, shedding a light on potential therapeutic strategy for ferroptosis-related pathologies.

[Research progress on the role of chondrocyte mitochondrial homeostasis imbalance in the pathogenesis of osteoarthritis]

Objective

To summarize the role of chondrocyte mitochondrial homeostasis imbalance in the pathogenesis of osteoarthritis (OA) and analyze its application prospects.

Methods

The recent literature at home and abroad was reviewed to summarize the mechanism of mitochondrial homeostasis imbalance, the relationship between mitochondrial homeostasis imbalance and the pathogenesis of OA, and the application prospect in the treatment of OA.

Results

Recent studies have shown that mitochondrial homeostasis imbalance, which is caused by abnormal mitochondrial biogenesis, the imbalance of mitochondrial redox, the imbalance of mitochondrial dynamics, and damaged mitochondrial autophagy of chondrocytes, plays an important role in the pathogenesis of OA. Abnormal mitochondrial biogenesis can accelerate the catabolic reaction of OA chondrocytes and aggravate cartilage damage. The imbalance of mitochondrial redox can lead to the accumulation of reactive oxygen species (ROS), inhibit the synthesis of extracellular matrix, induce ferroptosis and eventually leads to cartilage degradation. The imbalance of mitochondrial dynamics can lead to mitochondrial DNA mutation, decreased adenosine triphosphate production, ROS accumulation, and accelerated apoptosis of chondrocytes. When mitochondrial autophagy is damaged, dysfunctional mitochondria cannot be cleared in time, leading to ROS accumulation, which leads to chondrocyte apoptosis. It has been found that substances such as puerarin, safflower yellow, and astaxanthin can inhibit the development of OA by regulating mitochondrial homeostasis, which proves the potential to be used in the treatment of OA.

Conclusion

The mitochondrial homeostasis imbalance in chondrocytes is one of the most important pathogeneses of OA, and further exploration of the mechanisms of mitochondrial homeostasis imbalance is of great significance for the prevention 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.

Role of SIRT3 in mitochondrial biology and its therapeutic implications in neurodegenerative disorders

Sirtuin 3 (SIRT3), a mitochondrial deacetylase expressed preferentially in high-metabolic-demand tissues including the brain, requires NAD⁺ as a cofactor for catalytic activity. It regulates various processes such as energy homeostasis, redox balance, mitochondrial quality control, mitochondrial unfolded protein response (UPRmt), biogenesis, dynamics and mitophagy by altering protein acetylation status. Reduced SIRT3 expression or activity causes hyperacetylation of hundreds of mitochondrial proteins, which has been linked with neurological abnormalities, neuro-excitotoxicity and neuronal cell death. A body of evidence has suggested, SIRT3 activation as a potential therapeutic modality for age-related brain abnormalities and neurodegenerative disorders.

Reprogramming of Mitochondrial Respiratory Chain Complex by Targeting SIRT3-COX4I2 Axis Attenuates Osteoarthritis Progression

Mitochondrial homeostasis is of great importance for cartilage integrity and associated with the progression of osteoarthritis (OA); however, the underlying mechanisms are unknown. This study aims to investigate the role of mitochondrial deacetylation reaction and investigate the mechanistic relationship OA development. Silent mating type information regulation 2 homolog 3 (SIRT3) expression has a negative correlation with the severity of OA in both human arthritic cartilage and mice inflammatory chondrocytes. Global SIRT3 deletion accelerates pathological phenotype in post-traumatic OA mice, as evidenced by cartilage extracellular matrix collapse, osteophyte formation, and synovial macrophage M1 polarization. Mechanistically, SIRT3 prevents OA progression by targeting and deacetylating cytochrome c oxidase subunit 4 isoform 2 (COX4I2) to maintain mitochondrial homeostasis at the post-translational level. The activation of SIRT3 by honokiol restores cartilage metabolic equilibrium and protects mice from the development of post-traumatic OA. Collectively, the loss of mitochondrial SIRT3 is essential for the development of OA, whereas SIRT3-mediated proteins deacetylation of COX4I2 rescues OA-impaired mitochondrial respiratory chain functions to improve the OA phenotype. Herein, the induction of SIRT3 provides a novel therapeutic candidate for OA treatment.

Curcumin Ameliorates Age-Induced Tight Junction Impaired in Porcine Sertoli Cells by Inactivating the NLRP3 Inflammasome through the AMPK/SIRT3/SOD2/mtROS Signaling Pathway

Blood-testis barrier (BTB) made of concomitant junction apparatus between Sertoli cells (SCs) is crucial for spermatogenesis. The tight junction (TJ) function is impaired in SCs with age, exhibiting an intimate relationship to testicular dysfunction induced by age. In this study, compared with those in young boars, TJ proteins (i.e., Occludin, ZO-1, and plus Claudin-11) were discovered to have reduced expressions in testes, and spermatogenesis ability declined in old boars. An in vitro age model for D-gal-treated porcine SCs was established, the performance of Curcumin as a natural antioxidant and anti-inflammatory compound in affecting the TJ function of SCs was appraised, and related molecular mechanisms were exploited. The results manifested that 40 g/L D-gal downregulated ZO-1, Claudin-11, and Occludin in terms of the expression in SCs, whereas Curcumin restored such expressions in D-gal-treated SCs. Using the AMPK and SIRT3 inhibiters demonstrated that activation of the AMPK/SIRT3 pathway was associated with Curcumin, which not only rescued the expression of ZO-1, Occludin, Claudin-11, and SOD2 but also inhibited the production of mtROS and ROS and the activation of NLRP3 inflammasome and release of IL-1β in D-gal-treated SCs. Furthermore, with mtROS scavenger (mito-TEMPO), NLRP3 inhibitor (MCC950) plus IL-1Ra treatment ameliorated D-gal-caused TJ protein decline in SCs. In vivo data also showed that Curcumin alleviated TJ impairment in murine testes, improved D-gal-triggered spermatogenesis ability, and inactivated the NLRP3 inflammasome by virtue of the AMPK/SIRT3/mtROS/SOD2 signal transduction pathway. Given the above findings, a novel mechanism where Curcumin modulates BTB function to improve spermatogenesis ability in age-related male reproductive disorder is characterized.

Sirtuins in osteoarthritis: current understanding

Osteoarthritis (OA) is a common disease characterized by severe chronic joint pain, that imposes a large burden on elderly people. OA is a highly heterogeneous disease, and multiple etiologies contribute to its progression. Sirtuins (SIRTs) are Class III histone deacetylases (HDACs) that regulate a comprehensive range of biological processes such as gene expression, cell differentiation, and organism development, and lifespan. Over the past three decades, increasing evidence has revealed that SIRTs are not only important energy sensors but also protectors against metabolic stresses and aging, and an increasing number of studies have focused on the functions of SIRTs in OA pathogenesis. In this review, we illustrate the biological functions of SIRTs in OA pathogenesis from the perspectives of energy metabolism, inflammation, autophagy and cellular senescence. Moreover, we offer insights into the role played by SIRTs in regulating circadian rhythm, which has recently been recognized to be crucial in OA development. Here, we provide the current understanding of SIRTs in OA to guide a new direction for OA treatment exploration.

OGG1 in the Kidney: Beyond Base Excision Repair

8-Oxoguanine DNA glycosylase (OGG1) is a repair protein for 8-oxoguanine (8-oxoG) in eukaryotic atopic DNA. Through the initial base excision repair (BER) pathway, 8-oxoG is recognized and excised, and subsequently, other proteins are recruited to complete the repair. OGG1 is primarily located in the cytoplasm and can enter the nucleus and mitochondria to repair damaged DNA or to exert epigenetic regulation of gene transcription. OGG1 is involved in a wide range of physiological processes, such as DNA repair, oxidative stress, inflammation, fibrosis, and autophagy. In recent years, studies have found that OGG1 plays an important role in the progression of kidney diseases through repairing DNA, inducing inflammation, regulating autophagy and other transcriptional regulation, and governing protein interactions and functions during disease and injury. In particular, the epigenetic effects of OGG1 in kidney disease have gradually attracted widespread attention. This study reviews the structure and biological functions of OGG1 and the regulatory mechanism of OGG1 in kidney disease. In addition, the possibility of OGG1 as a potential therapeutic target in kidney disease is discussed.

The sirtuin family in health and disease

Sirtuins (SIRTs) are nicotine adenine dinucleotide(+)-dependent histone deacetylases regulating critical signaling pathways in prokaryotes and eukaryotes, and are involved in numerous biological processes. Currently, seven mammalian homologs of yeast Sir2 named SIRT1 to SIRT7 have been identified. Increasing evidence has suggested the vital roles of seven members of the SIRT family in health and disease conditions. Notably, this protein family plays a variety of important roles in cellular biology such as inflammation, metabolism, oxidative stress, and apoptosis, etc., thus, it is considered a potential therapeutic target for different kinds of pathologies including cancer, cardiovascular disease, respiratory disease, and other conditions. Moreover, identification of SIRT modulators and exploring the functions of these different modulators have prompted increased efforts to discover new small molecules, which can modify SIRT activity. Furthermore, several randomized controlled trials have indicated that different interventions might affect the expression of SIRT protein in human samples, and supplementation of SIRT modulators might have diverse impact on physiological function in different participants. In this review, we introduce the history and structure of the SIRT protein family, discuss the molecular mechanisms and biological functions of seven members of the SIRT protein family, elaborate on the regulatory roles of SIRTs in human disease, summarize SIRT inhibitors and activators, and review related clinical studies.

Sirt3 Promotes Chondrogenesis, Chondrocyte Mitochondrial Respiration and the Development of High-Fat Diet-Induced Osteoarthritis in Mice

Understanding how obesity-induced metabolic stress contributes to synovial joint tissue damage is difficult because of the complex role of metabolism in joint development, maintenance, and repair. Chondrocyte mitochondrial dysfunction is implicated in osteoarthritis (OA) pathology, which motivated us to study the mitochondrial deacetylase enzyme sirtuin 3 (Sirt3). We hypothesized that combining high-fat-diet (HFD)-induced obesity and cartilage Sirt3 loss at a young age would impair chondrocyte mitochondrial function, leading to cellular stress and accelerated OA. Instead, we unexpectedly found that depleting cartilage Sirt3 at 5 weeks of age using Sirt3-flox and Acan-Cre^ERT2 mice protected against the development of cartilage degeneration and synovial hyperplasia following 20 weeks of HFD. This protection was associated with increased cartilage glycolysis proteins and reduced mitochondrial fatty acid metabolism proteins. Seahorse-based assays supported a mitochondrial-to-glycolytic shift in chondrocyte metabolism with Sirt3 deletion. Additional studies with primary murine juvenile chondrocytes under hypoxic and inflammatory conditions showed an increased expression of hypoxia-inducible factor (HIF-1) target genes with Sirt3 deletion. However, Sirt3 deletion impaired chondrogenesis using a murine bone marrow stem/stromal cell pellet model, suggesting a context-dependent role of Sirt3 in cartilage homeostasis. Overall, our data indicate that Sirt3 coordinates HFD-induced changes in mature chondrocyte metabolism that promote OA. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Effects of mitochondrial dysfunction on bone metabolism and related diseases: a scientometric study from 2003 to 2022

Background

In recent years, mitochondrial dysfunction has been extensively studied and published, but research on the effects of mitochondrial dysfunction on bone metabolism and related diseases is only just beginning. Furthermore, no studies have been carried out to systematically illustrate this area from a scientometric point of view. The goal of this research is to review existing knowledge and identify new trends and possible hotspots in this area.

Methods

All publications related to the relationship between mitochondrial dysfunction and bone metabolism and related diseases from 2003 to 2022 were searched at the Web of Science Core Collection (WoSCC) on May 7, 2022. Four different analytical tools: VOSviewer 1.6.18, CiteSpace V 6.1, HistorCite (12.03.07), and Excel 2021 were used for the scientometric research.

Results

The final analysis included 555 valid records in total. Journal of Biological Chemistry (Co-citations = 916) is the most famous journal in this field. China (Percentage = 37%), the United States (Percentage = 24%), and Korea (Percentage = 12%) are the most productive countries. Blanco FJ and Choi EM are the main researchers with significant academic influence. Current research hotspots are basic research on mitochondrial dysfunction and the prevention or treatment of bone metabolism-related diseases.

Conclusion

The study of the consequences of mitochondrial dysfunction on bone metabolism and associated diseases is advancing rapidly. Several prominent researchers have published extensive literature and are widely cited. Future research in this area will focus on oxidative stress, aging, gene expression, and the pathogenesis of bone metabolism-related diseases.

Metformin as a potential disease-modifying drug in osteoarthritis: a systematic review of pre-clinical and human studies

OBJECTIVE

Osteoarthritis causes significant pain and disability with no approved disease-modifying drugs. We systematically reviewed the evidence from both pre-clinical and human studies for the potential disease-modifying effect of metformin in osteoarthritis.

METHODS

Ovid Medline, Embase and CINAHL were searched between inception and June 2021 using MeSH terms and key words to identify studies examining the association between metformin use and outcome measures related to osteoarthritis. Two reviewers performed the risk of bias assessment and 3 reviewers extracted data independently. Qualitative evidence synthesis was performed. This systematic review is registered on PROSPERO (CRD42021261052 and CRD42021261060).

RESULTS

Fifteen (10 pre-clinical and 5 human) studies were included. Most studies (10 pre-clinical and 3 human) assessed the effect of metformin using knee osteoarthritis models. In pre-clinical studies, metformin was assessed for the effect on structural outcomes (n = 10); immunomodulation (n = 5); pain (n = 4); and molecular pathways of its effect in osteoarthritis (n = 7). For human studies, metformin was evaluated for the effect on structural progression (n = 3); pain (n = 1); and immunomodulation (n = 1). Overall, pre-clinical studies consistently showed metformin having a chondroprotective, immunomodulatory and analgesic effect in osteoarthritis, predominantly mediated by adenosine monophosphate-activated protein kinase activation. Evidence from human studies, although limited, was consistent with findings in pre-clinical studies.

CONCLUSION

We found consistent evidence across pre-clinical and human studies to support a favourable effect of metformin on chondroprotection, immunomodulation and pain reduction in knee osteoarthritis. Further high-quality clinical trials are needed to confirm these findings as metformin could be a novel therapeutic drug for the treatment of osteoarthritis.

LONP1 downregulation with ageing contributes to osteoarthritis via mitochondrial dysfunction

Osteoarthritis (OA) is an age-related disorder and an important cause of disability that is characterized by a senescence-associated secretory phenotype and matrix degradation leading to a gradual loss of articular cartilage integrity. Mitochondria, as widespread organelles, are involved in regulation of complex biological processes such as energy synthesis and cell metabolism, which also have bidirectional communication with the nucleus to help maintain cellular homeostasis and regulate adaptation to a broad range of stressors. In light of the evidence that OA is strongly associated with mitochondrial dysfunction. In addition, mitochondria are considered to be the culprits of cell senescence, and mitochondrial function changes during ageing are considered to have a controlling role in cell fate. Mitochondrial dysfunction is also observed in age-related OA, however, the internal mechanism by which mitochondrial function changes with ageing to lead to the development of OA has not been elucidated. In this study, we found that the expression of Lon protease 1 (LONP1), a mitochondrial protease, was decreased in human OA cartilage and in ageing rat chondrocytes. Furthermore, LONP1 knockdown accelerated the progression and severity of osteoarthritis, which was associated with aspects of mitochondrial dysfunction including oxidative stress, metabolic changes and mitophagy, leading to downstream MAPK pathway activation. Antioxidant therapy with resveratrol suppressed oxidative stress and MAPK pathway activation induced by LONP1 knockdown to mitigate OA progression. Therefore, our findings demonstrate that LONP1 is a central regulator of mitochondrial function in chondrocytes and reveal that downregulation of LONP1 with ageing contributes to osteoarthritis.

HK2: a potential regulator of osteoarthritis via glycolytic and non-glycolytic pathways

Osteoarthritis (OA) is an age-related chronic degenerative joint disease where the main characteristics include progressive degeneration of cartilage, varying degrees of synovitis, and periarticular osteogenesis. However, the underlying factors involved in OA pathogenesis remain elusive which has resulted in poor clinical treatment effect. Recently, glucose metabolism changes provide a new perspective on the pathogenesis of OA. Under the stimulation of external environment, the metabolic pathway of chondrocytes tends to change from oxidative phosphorylation (OXPHOS) to aerobic glycolysis. Previous studies have demonstrated that glycolysis of synovial tissue is increased in OA. The hexokinase (HK) is the first rate limiting enzyme in aerobic glycolysis, participating and catalyzing the main pathway of glucose utilization. An isoform of HKs, HK2 is considered to be a key regulator of glucose metabolism, promotes the transformation of glycolysis from OXPHOS to aerobic glycolysis. Moreover, the expression level of HK2 in OA synovial tissue (FLS) was higher than that in control group, which indicated the potential therapeutic effect of HK2 in OA. However, there is no summary to help us understand the potential therapeutic role of glucose metabolism in OA. Therefore, this review focuses on the properties of HK2 and existing research concerning HK2 and OA. We also highlight the potential role and mechanism of HK2 in OA.

The effects of metformin in the treatment of osteoarthritis: Current perspectives

Osteoarthritis is a chronic and irreversible disease of the locomotor system which is closely associated with advancing age. Pain and limited mobility frequently affect the quality of life in middle-aged and older adults. With a global population of more than 350 million, osteoarthritis is becoming a health threat alongside cancer and cardiovascular disease. It is challenging to find effective treatments to promote cartilage repair and slow down disease progression. Metformin is the first-line drug for patients with type 2 diabetes, and current perspectives suggest that it cannot only lower glucose but also has anti-inflammatory and anti-aging properties. Experimental studies applying metformin for the treatment of osteoarthritis have received much attention in recent years. In our review, we first presented the history of metformin and the current status of osteoarthritis, followed by a brief review of the mechanism that metformin acts, involving AMPK-dependent and non-dependent pathways. Moreover, we concluded that metformin may be beneficial in the treatment of osteoarthritis by inhibiting inflammation, modulating autophagy, antagonizing oxidative stress, and reducing pain levels. Finally, we analyzed the relevant evidence from animal and human studies. The potential of metformin for the treatment of osteoarthritis deserves to be further explored.

Ononin alleviates endoplasmic reticulum stress in doxorubicin-induced cardiotoxicity by activating SIRT3

Doxorubicin (DOX) is a potent anthracycline antineoplastic drug. However, its dose-dependent cardiotoxicity limits its clinical application. Ononin is a natural isoflavone glycoside that is crucial in modulating apoptosis-related signaling pathways. In this study, we assessed the possible cardioprotective effects of ononin in DOX-induced cardiotoxicity and elucidated the underlying molecular mechanisms. In vitro and in vivo assessments were performed using DOX-treated H9C2 cells and rats, respectively. First, DOX was injected into the tail veins of Wistar rats to induce cardiomyopathy. Next, rats in the DOX + Ononin30 and DOX + Ononin60 groups were intragastrically administered ononin two weeks before DOX treatment. H9C2 cells were treated with vehicle or DOX with or without ononin. Next, 3-TYP was used to determine the relationship between endoplasmic reticulum (ER) stress and sirtuin 3 (SIRT3) expression. Ononin treatment ameliorated DOX-induced myocardial injury as determined by echocardiography. Furthermore, ononin partially restored DOX-induced cardiac dysfunction; the left ventricular ejection fraction (LVEF) and left ventricular systolic fractional shortening (LVFS) increased after pre-treatment with ononin. Further, ononin suppressed DOX-induced ER stress and apoptosis in rat cardiomyocytes and H9C2 cells. The Bax/Bcl-2 ratio and 78-kD glucose-regulated protein (GRP78) and CCAAT enhancer-binding protein (CHOP) expression levels were higher in the DOX-treated group than in the control group but ononin treatment improved these parameters. These effects are associated with SIRT3 activity. Moreover, 3-TYP blocked the ononin-mediated protective effects. Hence, ononin positively affected DOX-induced cardiotoxicity by inhibiting ER stress and apoptosis, possibly mediated by stimulation of the SIRT3 pathway.

Metformin mitigates stress-induced premature senescence by upregulating AMPKα at Ser485 phosphorylation induced SIRT3 expression and inactivating mitochondrial oxidants

The senescence of vascular smooth muscle cells (VSMCs) is an important cause of cardiovascular disease such as atherosclerosis and hypertension. These senescence may be triggered by many factors, such as oxidative stress, inflammation, DNA damage, and senescence-associated secretory phenotypes (SASPs). Mitochondrial oxidative stress induces cellular senescence, but the mechanisms by which mitochondrial reactive oxygen species (mtROS) regulates cellular senescence are still largely unknown. Here, we investigated the mechanism responsible for the anti-aging effect of metformin by examining links between VSMC senescence and mtROS in in vitro and in vivo. Metformin was found to increase p-AMPK (Ser485), but to decrease senescence-associated phenotypes and protein levels of senescence markers during ADR-induced VSMC senescence. Importantly, metformin decreased mtROS by inducing the deacetylation of superoxide dismutase 2 (SOD2) by increasing SIRT3 expression. Moreover, AMPK depletion reduced the expression of SIRT3 and increased the expression of acetylated SOD2 despite metformin treatment, suggesting AMPK activation by metformin is required to protect against mitochondrial oxidative stress by SIRT3. This study provides mechanistic evidence that metformin acts as an anti-aging agent and alleviates VSMC senescence by upregulating mitochondrial antioxidant induced p-AMPK (Ser485)-dependent SIRT3 expression, which suggests metformin has therapeutic potential for the treatment of age-associated vascular disease.

Potential Methods of Targeting Cellular Aging Hallmarks to Reverse Osteoarthritic Phenotype of Chondrocytes

Osteoarthritis (OA) is a chronic degenerative joint disease that causes pain, physical disability, and life quality impairment. The pathophysiology of OA remains largely unclear, and currently no FDA-approved disease-modifying OA drugs (DMOADs) are available. As has been acknowledged, aging is the primary independent risk factor for OA, but the mechanisms underlying such a connection are not fully understood. In this review, we first revisit the changes in OA chondrocytes from the perspective of cellular hallmarks of aging. It is concluded that OA chondrocytes share many alterations similar to cellular aging. Next, based on the findings from studies on other cell types and diseases, we propose methods that can potentially reverse osteoarthritic phenotype of chondrocytes back to a healthier state. Lastly, current challenges and future perspectives are summarized.

The Role of Mitochondrial Metabolism, AMPK-SIRT Mediated Pathway, LncRNA and MicroRNA in Osteoarthritis

Osteoarthritis (OA) is the most common joint disease characterized by degeneration of articular cartilage and causes severe joint pain, physical disability, and impaired quality of life. Recently, it was found that mitochondria not only act as a powerhouse of cells that provide energy for cellular metabolism, but are also involved in crucial pathways responsible for maintaining chondrocyte physiology. Therefore, a growing amount of evidence emphasizes that impairment of mitochondrial function is associated with OA pathogenesis; however, the exact mechanism is not well known. Moreover, the AMP-activated protein kinase (AMPK)–Sirtuin (SIRT) signaling pathway, long non-coding RNA (lncRNA), and microRNA (miRNA) are important for regulating the physiological and pathological processes of chondrocytes, indicating that these may be targets for OA treatment. In this review, we first focus on the importance of mitochondria metabolic dysregulation related to OA. Then, we show recent evidence on the AMPK-SIRT mediated pathway associated with OA pathogenesis and potential treatment options. Finally, we discuss current research into the effects of lncRNA and miRNA on OA progression or inhibition.

POLG mutations lead to abnormal mitochondrial remodeling during neural differentiation of human pluripotent stem cells via SIRT3/AMPK pathway inhibition

We showed previously that POLG mutations cause major changes in mitochondrial function, including loss of mitochondrial respiratory chain (MRC) complex I, mitochondrial DNA (mtDNA) depletion and an abnormal NAD⁺/NADH ratio in both neural stem cells (NSCs) and astrocytes differentiated from induced pluripotent stem cells (iPSCs). In the current study, we looked at mitochondrial remodeling as stem cells transit pluripotency and during differentiation from NSCs to both dopaminergic (DA) neurons and astrocytes comparing the process in POLG-mutated and control stem cells. We saw that mitochondrial membrane potential (MMP), mitochondrial volume, ATP production and reactive oxygen species (ROS) changed in similar ways in POLG and control NSCs, but mtDNA replication, MRC complex I and NAD⁺ metabolism failed to remodel normally. In DA neurons differentiated from NSCs, we saw that POLG mutations caused failure to increase MMP and ATP production and blunted the increase in mtDNA and complex I. Interestingly, mitochondrial remodeling during astrocyte differentiation from NSCs was similar in both POLG-mutated and control NSCs. Further, we showed downregulation of the SIRT3/AMPK pathways in POLG-mutated cells, suggesting that POLG mutations lead to abnormal mitochondrial remodeling in early neural development due to the downregulation of these pathways. [Figure: see text].

Sirt3 ameliorates mitochondrial dysfunction and oxidative stress through regulating mitochondrial biogenesis and dynamics in cardiomyoblast

Sirtuins are the endogenously present anti-aging protein deacetylases that regulate the mitochondrial biogenesis and function. Especially Sirt3, a mitochondrial sirtuin, is well known for maintaining mitochondrial function and health. In the present study, we have explored the novel role of Sirt3 in mitochondrial biogenesis and shown the role of Sirt3 in mito-nuclear communication through AMPK-α in Sirt3 knockdown and Sirt3 overexpressed H9c2 cells. The study found that impaired mitochondrial function in Sirt3-knockdown H9c2 cells was associated with decreased expression of mitochondrial DNA encoded genes, reduced SOD2 expression and activity. The study also revealed that Sirt3 knockdown affects mitochondrial biogenesis and dynamics. To further confirm the role of Sirt3 on mitochondrial biogenesis and health, we did Sirt3 overexpression in H9c2 cells. Sirt3 overexpression enhanced the expression of mitochondrial DNA encoded genes, increased SOD2 activity and altered mitochondrial dynamics. Sirt3 overexpression also caused an increase in mitochondrial biogenesis gene and protein (PGC-1α and TFAM) expression. All these changes were confirmed with mitochondrial functional parameters like basal respiration, maximal respiratory capacity, spare respiratory capacity and ATP production. We found decreased mitochondrial function in Sirt3-knockdown H9c2 cells when compared to control H9c2 cells. Together our data conclude that Sirt3 regulates cardiac mitochondrial health and function through the Sirt3-AMPKα-PGC-1α axis.

Advanced Glycation End Products Induced Mitochondrial Dysfunction of Chondrocytes through Repression of AMPKα-SIRT1-PGC-1α Pathway

INTRODUCTION

Our previous studies have demonstrated advanced glycation end products (AGEs) was an important mediator in osteoarthritis (OA) which may induce mitochondrial dysfunction. AMP-activated protein kinase (AMPK), sirtuin 1 (SIRT1), and its downstream target peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) are the critical sensors that regulate mitochondrial biogenesis and have been recognized as therapeutic targets in OA. This study was designed to test whether AGEs caused mitochondrial dysfunction through modulation of AMPKα/SIRT1/PGC-1α.

METHODS

We knocked down or overexpressed AMPKα, SIRT1, and PGC-1α by small interfering RNA or plasmid DNA transfection, respectively. Mitochondrial membrane potential (△Ψ) was detected by tetraethylbenzimidazolyl carbocyanine iodide (JC-1) fluorescence probe.

RESULTS

The results showed that AGEs impaired △Ψ, intracellular ATP level, and mitochondrial DNA content, linked to decreased AMPKα, SIRT1, and PGC-1α expression in chondrocyte. AMPKα pharmacologic activation or overexpression of AMPKα, SIRT1, and PGC-1α reversed impairments of mitochondrial biogenesis, oxidative stress, and inflammation in AGEs-induced chondrocytes. However, AMPKα activation using AICAR had decreased capacity to increase each of those same effect readouts in AGEs-treated SIRT1-siRNA or PGC-1α-siRNA chondrocyte.

CONCLUSION

Taken together, AGEs reduced the AMPKα/SIRT1/PGC-1α signaling in chondrocytes, leading to mitochondrial dysfunction as a result of increased oxidative stress, inflammation, and apoptosis. These results indicated that target AMPK may be as a novel therapeutic strategy for AGEs-related OA prevention.

Mitochondrial quality control in cartilage damage and osteoarthritis: new insights and potential therapeutic targets

Osteoarthritis (OA) is a multifactorial arthritic disease of weight-bearing joints concomitant with chronic and intolerable pain, loss of locomotion and impaired quality of life in the elderly population. Although the prevalence of OA increases with age, its specific mechanisms have not been elucidated and effective therapeutic disease-modifying drugs have not been developed. As essential organelles in chondrocytes, mitochondria supply energy and play vital roles in cellular metabolism, proliferation and apoptosis. Mitochondrial quality control (MQC) is the key mechanism to coordinate various mitochondrial biofunctions, primarily through mitochondrial biogenesis, dynamics, autophagy and the newly discovered mitocytosis. An increasing number of studies have revealed that a loss of MQC homeostasis contributes to the cartilage damage during the occurrence and development of OA. Several master MQC-associated signaling pathways and regulators exert chondroprotective roles in OA, while cartilage damage-related molecular mechanisms have been partially identified. In this review, we summarized known mechanisms mediated by dysregulated MQC in the pathogenesis of OA and latent bioactive ingredients and drugs for the prevention and treatment of OA through the maintenance of MQC.

SIRT3-AMPK signaling pathway as a protective target in endothelial dysfunction of early sepsis

Extensive vascular endothelial dysfunction usually occurs in sepsis, resulting in high mortality. The purpose of this study was therefore to investigate the role of AMP-dependent protein kinase (AMPK) in the aortic endothelial dysfunction of early sepsis in mice, and the relationship between AMPK and Sirtuin3 (SIRT3). Cecal ligation and puncture (CLP) surgery was performed to establish a mouse sepsis model, and human umbilical vein endothelial cells (HUVECs) were treated with lipopolysaccharide (LPS) to mimic a sepsis model in vitro. We suppressed and increased the activities of AMPK with Dorsomorphin (CC) and Acadesine (AICAR), respectively. 3-TYP (SIRT3 inhibitor) and Honokiol (SIRT3 agonist) were used to alter SIRT3 activity. Then, the inflammatory and endothelial function parameters of the vascular tissue and survival rate were determined. In vivo, the expression of Ser1177 phosphorylation of endothelial nitric oxide synthase (p-eNOS), endothelium-dependent relaxation function, and survival decreased (P < 0.05), while NF-κB and NLRP3 pathways were activated in CLP-induced early sepsis (P < 0.05). Moreover, activation of AMPK significantly reversed the reduction of p-eNOS expression (P < 0.05), prevented endothelial dysfunction (P < 0.05), deactivated NF-κB and NLRP3 pathways (P < 0.05), and improved survival (P < 0.05) in septic mice. However, AMPK inhibition led to opposite effects (P < 0.05). In addition, changing the activity of AMPK had little effect on SIRT3 expression (P > 0.05), while the expression of p-AMPK varied with the inhibition or activation of SIRT3 (P < 0.05), which was further demonstrated using in vitro experiments. Together, the results showed that the SIRT3-AMPK signaling pathway played an important role in inhibiting vascular inflammation and endothelial dysfunction during early sepsis.

[The role of chondrocyte mitochondrial biogenesis in the pathogenesis of osteoarthritis]

OBJECTIVE

To summarize the role of chondrocytes mitochondrial biogenesis in the pathogenesis of osteoarthritis (OA), and analyze the applications in the treatment of OA.

METHODS

A review of recent literature was conducted to summarize the changes in mitochondrial biogenesis in the course of OA, the role of major signaling molecules in OA chondrocytes, and the prospects for OA therapeutic applications.

RESULTS

Recent studies reveales that mitochondria are significant energy metabolic centers in chondrocytes and its dysfunction has been considered as an essential mechanism in the pathogenesis of OA. Mitochondrial biogenesis is one of the key processes maintaining the normal quantity and function of mitochondria, and peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) is the central regulator of this process. A regulatory network of mitochondrial biogenesis with PGC-1α as the center, adenosine monophosphate-activated protein kinase, sirtuin1/3, and cyclic adenosine monophosphate response element-binding protein as the main upstream regulatory molecules, and nuclear respiratory factor 1, estrogen-related receptor α, and nuclear respiratory factor 2 as the main downstream regulatory molecules has been reported. However, the role of mitochondrial biogenesis in OA chondrocytes still needs further validation and in-depth exploration. It has been demonstrated that substances such as puerarin and omentin-1 can retard the development of OA by activating the damaged mitochondrial biogenesis in OA chondrocytes, which proves the potential to be used in the treatment OA.

CONCLUSION

Mitochondrial biogenesis in chondrocytes plays an important role in the pathogenesis of OA, and further exploring the related mechanisms is of great clinical significance.

Oral administration of berberine limits post-traumatic osteoarthritis development and associated pain via AMP-activated protein kinase (AMPK) in mice

OBJECTIVE

We investigated the effect of berberine, a natural plant product that can activate AMP-activated protein kinase (AMPK), on Osteoarthritis (OA) development and associated pain in mice.

DESIGN

Human primary knee chondrocytes were utilized to investigate how AMPK is activated by berberine. Both global knockout (KO) of AMPKα1 and congenic wild type (WT) mice were subjected to the post-traumatic OA through destabilization of medial meniscus (DMM) surgery. Two weeks after surgery, the mice were randomly divided into two groups with one group receiving berberine chloride daily via drinking water and were sacrificed at 6 and 12 weeks after surgery. OA severity was assessed by histological and histomorphometric analyses of cartilage degradation, synovitis, and osteophyte formation. OA-associated pain behavior was also determined. Immunohistochemistry (IHC) analyses were carried out to examine changes in AMPK signaling.

RESULTS

Berberine induced phosphorylation of AMPKα (Thr172) via liver kinase B1 (LKB1), the major upstream kinase of AMPK, in chondrocytes in vitro. Both WT and AMPKα1KO developed OA and associated pain post DMM surgery. However, treatment with berberine significantly reduced severity of OA and associated pain in WT but not AMPKα1KO mice. IHC analysis of WT DMM knee cartilage further revealed that berberine inhibited concomitant loss of expression and phosphorylation of AMPKα and expression of SIRT1 and SIRT3, suggesting an important role of activation of AMPK signaling in mediating beneficial effect of berberine.

CONCLUSIONS

Berberine acts through AMPK to reduce joint structural damage and pain associated with post-traumatic OA in mice in vivo.

Ginsenoside Rg3 Attenuates TNF-α-Induced Damage in Chondrocytes through Regulating SIRT1-Mediated Anti-Apoptotic and Anti-Inflammatory Mechanisms

The upregulation of tumor necrosis factor-alpha (TNF-α) is a common event in arthritis, and the subsequent signaling cascade that leads to tissue damage has become the research focus. To explore a potential therapeutic strategy to prevent cartilage degradation, we tested the effect of ginsenoside Rg3, a bioactive component of Panax ginseng, on TNF-α-stimulated chondrocytes.TC28a2 Human Chondrocytes were treated with TNF-α to induce damage of chondrocytes. SIRT1 and PGC-1a expression levels were investigated by Western blotting assay. Mitochondrial SIRT3 and acetylated Cyclophilin D (CypD) were investigated using mitochondrial isolation. The mitochondrial mass number and mitochondrial DNA copy were studied for mitochondrial biogenesis. MitoSOX and JC-1 were used for the investigation of mitochondrial ROS and membrane potential. Apoptotic markers, pro-inflammatory events were also tested to prove the protective effects of Rg3. We showed Rg3 reversed the TNF-α-inhibited SIRT1 expression. Moreover, the activation of the SIRT1/PGC-1α/SIRT3 pathway by Rg3 suppressed the TNF-α-induced acetylation of CypD, resulting in less mitochondrial dysfunction and accumulation of reactive oxygen species (ROS). Additionally, we demonstrated that the reduction of ROS ameliorated the TNF-α-elicited apoptosis. Furthermore, the Rg3-reverted SIRT1/PGC-1α/SIRT3 activation mediated the repression of p38 MAPK, which downregulated the NF-κB translocation in the TNF-α-treated cells. Our results revealed that administration of Rg3 diminished the production of interleukin 8 (IL-8) and matrix metallopeptidase 9 (MMP-9) in chondrocytes via SIRT1/PGC-1α/SIRT3/p38 MAPK/NF-κB signaling in response to TNF-α stimulation. Taken together, we showed that Rg3 may serve as an adjunct therapy for patients with arthritis.

[Research Progress in Glucose Metabolism of Chondrocytes]

Chondrocytes have a limited supply of glucose and oxygen for metabolism since articular cartilages are relatively avascular. We herein reviewed the characteristics of chondrocyte glucose metabolism and the new research progress in chondrocyte glucose metabolism in the osteoarthritis process. Current research has shown that chondrocytes obtain glucose from synovial fluids and subchondral bones, take in glucose via specific glucose transporters, and metabolize glucose mainly through glycolysis and mitochondrial respiration to produce adenosine triphosphate (ATP). Glucose metabolism in chondrocytes is distinctive because it relies much more on glycolysis rather than mitochondrial respiration for ATP production, and shows Warburg effect and Crabtree effect. In osteoarthritic chondrocytes, the glucose metabolism disorder is presented as further suppression of mitochondrial respiration, over-active or impaired glycolysis, and decreased total production of ATP. However, the significance of the glucose supply for chondrocytes from synovial fluids and subchondral bones remains undefined. There are still disputes in the understanding of the changes in glycolytic pathways in osteoarthritic chondrocytes. Therefore, future research is needed to explore the characteristics of glucose metabolism in normal and osteoarthritic chondrocytes in order to develop new diagnostic and therapeutic strategies for osteoarthritis.

circFAM160A2 Promotes Mitochondrial Stabilization and Apoptosis Reduction in Osteoarthritis Chondrocytes by Targeting miR-505-3p and SIRT3

Competitive endogenous RNAs (ceRNAs), as a newly identified regulating mechanism, have been demonstrated to play a crucial role in various human diseases. An increasing number of recent studies have revealed that circular RNAs (circRNAs) can function as ceRNAs. However, little is known about the role of circFAM160A2 in the pathological process of osteoarthritis (OA). This study is the first to examine the crucial role of the circFAM160A2-miR-505-3p-SIRT3 axis in osteoarthritis progression. miR-505-3p was selected from the interaction of a microRNA (miRNA) microarray comparing chondrocytes in OA and normal conditions and prediction results from TargetScan. RT-qPCR was performed to assess the expression of circFAM160A2, miR-505-3p, and SIRT3. A dual luciferase assay was used to validate the binding of circFAM160A2, miR-505-3p, and SIRT3. We used lentivirus and adeno-associated virus to establish in vitro and in vivo overexpression models. Western blotting, apoptosis assay, ROS detection assay, Safranin O staining, and CCK-8 assay were employed to assess the role of circFAM160A2, miR-505-3p, and SIRT3. We found that miR-505-3p was upregulated and circFAM160A2 was downregulated in OA. While overexpression of circFAM160A2 decreased the production of extracellular matrix (ECM) degrading enzymes and ameliorated chondrocyte apoptosis and mitochondrial dysfunction, inhibition of miR-505-3p could reverse the protective effect of circFAM160A2 on the OA phenotype both in vitro and in vivo. In conclusion, circFAM160A2 can promote mitochondrial stabilization and apoptosis reduction in OA chondrocytes by targeting miR-505-3p and SIRT3, which might be a potential therapeutic target for OA therapy.