Estrogen protects against acidosis-mediated articular chondrocyte injury by promoting ASIC1a protein degradation

Inhibition of ASIC1a reduces ferroptosis in rheumatoid arthritis articular chondrocytes via the p53/NRF2/SLC7A11 pathway

The activation of acid-sensing ion channel 1a (ASIC1a) in response to extracellular acidification leads to an increase in extracellular calcium influx, thereby exacerbating the degeneration of articular chondrocytes in rheumatoid arthritis (RA). It has been suggested that the inhibition of extracellular calcium influx could potentially impede chondrocyte ferroptosis. The cystine transporter, solute carrier family 7 member 11 (SLC7A11), is recognized as a key regulator of ferroptosis. Recent studies suggest that the tumor suppressor gene p53 facilitates the induction of ferroptosis by suppressing the upregulation of SLC7A11. This process is mediated by the nuclear factor erythroid 2-related factor 2 (NRF2), a key transcription factor integral to the maintenance of cellular redox homeostasis and the regulation of inflammatory responses. This study aims to investigate the role of ASIC1a in the ferroptosis of RA chondrocytes and to determine the involvement of the p53/NRF2/SLC7A11 pathway in its underlying mechanism. In vitro experiments revealed that acidosis induces ferroptosis and reduces the expression of NRF2 and SLC7A11 in chondrocytes. Moreover, acidification significantly increased p53 protein levels in chondrocytes. Pifithrin-α (PFN-α), a p53 inhibitor, mitigated acidosis-induced ferroptosis and restored the diminished expression of NRF2 and SLC7A11. Furthermore, PcTx-1, an ASIC1a inhibitor, inhibited acidification-induced ferroptosis, enhanced the protein levels of SLC7A11 and NRF2, and reduced p53 expression. In vivo experiments demonstrated that the ASIC1a-specific inhibitor PcTx-1 ameliorated histopathological characteristics of ankle joints in collagen-induced arthritis (CIA) mice, decreased p53 expression, and enhanced NRF2 and SLC7A11 expression in chondrocytes. These findings suggest that ASIC1a inhibition may mitigate acidification-induced ferroptosis in articular chondrocytes in RA, potentially via the p53/NRF2/SLC7A11 pathway.

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.

Metabolic Acidosis Results in Sexually Dimorphic Response in the Heart Tissue

Metabolic acidosis (MA) is a highly prevalent disorder in a significant proportion of the population, resulting from imbalance in blood pH homeostasis. The heart, being an organ with very low regenerative capacity and high metabolic activity, is vulnerable to chronic, although low-grade, MA. To systematically characterize the effect of low-grade MA on the heart, we treated male and female mice with NH4Cl supplementation for 2 weeks and analyzed their blood chemistry and transcriptomic signature of the heart tissue. The reduction of pH and plasma bicarbonate levels without an associated change in anion gap indicated a physiological manifestation of low-grade MA with minimal respiratory compensation. On transcriptomic analysis, we observed changes in cardiac-specific genes with significant gender-based differences due to MA. We found many genes contributing to dilated cardiomyopathy to be altered in males, more than in females, while cardiac contractility and Na/K/ATPase-Src signaling were affected in the opposite way. Our model presents a systems-level understanding of how the cardiovascular tissue is affected by MA. As low-grade MA is a common ailment with many dietary and pharmaceutical interventions, our work presents avenues to limit chronic cardiac damage and disease manifestation, as well as highlighting the sex differences in MA-induced cardiovascular damage.

Sex-dependent variation in cartilage adaptation: from degeneration to regeneration

Despite acknowledgement in the scientific community of sex-based differences in cartilage biology, the implications for study design remain unclear, with many studies continuing to arbitrarily assign demographics. Clinically, it has been well-established that males and females differ in cartilage degeneration, and accumulating evidence points to the importance of sex differences in the field of cartilage repair. However, a comprehensive review of the mechanisms behind this trend and the influence of sex on cartilage regeneration has not yet been presented. This paper aims to summarize current findings regarding sex-dependent variation in knee anatomy, sex hormones' effect on cartilage, and cartilaginous degeneration and regeneration, with a focus on stem cell therapies. Findings suggest that the stem cells themselves, as well as their surrounding microenvironment, contribute to sex-based differences. Accordingly, this paper underscores the contribution of both stem cell donor and recipient sex to sex-related differences in treatment efficacy. Cartilage regeneration is a field that needs more research to optimize strategies for better clinical results; taking sex into account could be a big factor in developing more effective and personalized treatments. The compilation of this information emphasizes the importance of investing further research in sex differences in cartilage biology.

Estrogen antagonizes ASIC1a-induced chondrocyte mitochondrial stress in rheumatoid arthritis

BACKGROUND

Destruction of articular cartilage and bone is the main cause of joint dysfunction in rheumatoid arthritis (RA). Acid-sensing ion channel 1a (ASIC1a) is a key molecule that mediates the destruction of RA articular cartilage. Estrogen has been proven to have a protective effect against articular cartilage damage, however, the underlying mechanisms remain unclear.

METHODS

We treated rat articular chondrocytes with an acidic environment, analyzed the expression levels of mitochondrial stress protein HSP10, ClpP, LONP1 by q-PCR and immunofluorescence staining. Transmission electron microscopy was used to analyze the mitochondrial morphological changes. Laser confocal microscopy was used to analyze the Ca²⁺, mitochondrial membrane potential (Δψm) and reactive oxygen species (ROS) level. Moreover, ASIC1a specific inhibitor Psalmotoxin 1 (Pctx-1) and Ethylene Glycol Tetraacetic Acid (EGTA) were used to observe whether acid stimulation damage mitochondrial function through Ca²⁺ influx mediated by ASIC1a and whether pretreatment with estrogen could counteract these phenomena. Furthermore, the ovariectomized (OVX) adjuvant arthritis (AA) rat model was treated with estrogen to explore the effect of estrogen on disease progression.

RESULTS

Our results indicated that HSP10, ClpP, LONP1 protein and mRNA expression and mitochondrial ROS level were elevated in acid-stimulated chondrocytes. Moreover, acid stimulation decreased mitochondrial membrane potential and damaged mitochondrial structure of chondrocytes. Furthermore, ASIC1a specific inhibitor PcTx-1 and EGTA inhibited acid-induced mitochondrial abnormalities. In addition, estrogen could protect acid-stimulated induced mitochondrial stress by regulating the activity of ASIC1a in rat chondrocytes and protects cartilage damage in OVX AA rat.

CONCLUSIONS

Extracellular acidification induces mitochondrial stress by activating ASIC1a, leading to the damage of rat articular chondrocytes. Estrogen antagonizes acidosis-induced joint damage by inhibiting ASIC1a activity. Our study provides new insights into the protective effect and mechanism of action of estrogen in RA.

Autophagy: An important target for natural products in the treatment of bone metabolic diseases

Bone homeostasis depends on a precise dynamic balance between bone resorption and bone formation, involving a series of complex and highly regulated steps. Any imbalance in this process can cause disturbances in bone metabolism and lead to the development of many associated bone diseases. Autophagy, one of the fundamental pathways for the degradation and recycling of proteins and organelles, is a fundamental process that regulates cellular and organismal homeostasis. Importantly, basic levels of autophagy are present in all types of bone-associated cells. Due to the cyclic nature of autophagy and the ongoing bone metabolism processes, autophagy is considered a new participant in bone maintenance. Novel therapeutic targets have emerged as a result of new mechanisms, and bone metabolism can be controlled by interfering with autophagy by focusing on certain regulatory molecules in autophagy. In parallel, several studies have reported that various natural products exhibit a good potential to mediate autophagy for the treatment of metabolic bone diseases. Therefore, we briefly described the process of autophagy, emphasizing its function in different cell types involved in bone development and metabolism (including bone marrow mesenchymal stem cells, osteoblasts, osteocytes, chondrocytes, and osteoclasts), and also summarized research advances in natural product-mediated autophagy for the treatment of metabolic bone disease caused by dysfunction of these cells (including osteoporosis, rheumatoid joints, osteoarthritis, fracture nonunion/delayed union). The objective of the study was to identify the function that autophagy serves in metabolic bone disease and the effects, potential, and challenges of natural products for the treatment of these diseases by targeting autophagy.

Acid-sensitive ion channel 1a mediates osteoarthritis chondrocyte senescence by promoting Lamin B1 degradation

Osteoarthritis (OA) is a common and debilitating chronic joint disease, which is characterized by degeneration of articular cartilage and the aging of chondrocytes. Acid-sensitive ion channel 1a (ASIC1a) is a proton-activated cationic channel abundant in chondrocytes, which senses and regulates joint cavity pH. Our previous study demonstrated that ASIC1a was involved in acid-induced rat articular chondrocyte senescence, but the mechanistic basis remained unclear. In this study, we explored the mechanism of ASIC1a in chondrocyte senescence and OA. The results showed that senescence-related-β-galactosidase, senescence-related markers (p53 and p21) and the autophagy-related protein Beclin-1 were found to be increased, but Lamin B1 was found to be reduced with acid (pH 6.0) treatment. These effects were inhibited by ASIC1a-specific blocker psalmotoxin-1 or ASIC1a-short hairpin RNA respectively in chondrocytes. Moreover, Silencing of Lamin B1 enhanced ASIC1a-mediated chondrocyte senescence, this effect was reversed by overexpression of Lamin B1, indicating that Lamin B1 was involved in ASIC1a-mediated chondrocyte senescence. Further, blockade of ASIC1a inhibits acid-induced autophagosomes and Beclin-1 protein expression, suggesting that ASIC1a is involved in acid-induced chondrocyte autophagy. Blocking autophagy with chloroquine inhibited Beclin-1 and increased Lamin B1 in acid-induced chondrocyte senescence. We further demonstrated that ASIC1a-mediated reduction of Lamin B1 expression was caused by autophagy pathway-dependent protein degradation. Finally, blocking ASIC1a protected cartilage tissue, restored Lamin B1 levels and inhibited chondrocyte senescence in a rat OA model. In summary, these findings suggest that ASIC1a may promote Lamin B1 degradation to mediate osteoarthritis chondrocyte senescence through the autophagy pathway.

Case Report: Danon Disease: Six Family Members and Literature Review

Danon disease is a rare X-linked dominant genetic disorder that manifests with a clinical triad of cardiomyopathy, skeletal myopathy, and intellectual disability. It is caused by mutations in the lysosome-associated membrane 2 (LAMP2) gene. We report one case of Danon disease and his family members, characterized by ventricular pre-excitation, ventricular hypertrophy, abnormal muscle enzymes, and aberrant liver function. All the patients were confirmed to have Danon disease through genetic screening. Relevant literature was reviewed as a reference for the diagnosis and treatment of the disease.

AcidoCEST-UTE MRI Reveals an Acidic Microenvironment in Knee Osteoarthritis

A relationship between an acidic pH in the joints, osteoarthritis (OA), and pain has been previously demonstrated. Acidosis Chemical Exchange Saturation Transfer (acidoCEST) indirectly measures the extracellular pH through the assessment of the exchange of protons between amide groups on iodinated contrast agents and bulk water. It is possible to estimate the extracellular pH in the osteoarthritic joint using acidoCEST MRI. However, conventional MR sequences cannot image deep layers of cartilage, meniscus, ligaments, and other musculoskeletal tissues that present with short echo time and fast signal decay. Ultrashort echo time (UTE) MRI, on the other hand, has been used successfully to image those joint tissues. Here, our goal is to compare the pH measured in the knee joints of volunteers without OA and patients with severe OA using acidoCEST-UTE MRI. Patients without knee OA and patients with severe OA were examined using acidoCEST-UTE MRI and the mean pH of cartilage, meniscus, and fluid was calculated. Additionally, the relationship between the pH measurements and the Knee Injury and Osteoarthritis Outcome Score (KOOS) was investigated. AcidoCEST-UTE MRI can detect significant differences in the pH of knee cartilage, meniscus, and fluid between joints without and with OA, with OA showing lower pH values. In addition, symptoms and knee-joint function become worse at lower pH measurements.

DNA Methylation of T Lymphocytes as a Therapeutic Target: Implications for Rheumatoid Arthritis Etiology

Rheumatoid arthritis (RA) is an autoimmune disease that can cause joint damage and disability. Epigenetic variation, especially DNA methylation, has been shown to be involved in almost all the stages of the pathology of RA, from autoantibody production to various self-effector T cells and the defects of protective T cells that can lead to chronic inflammation and erosion of bones and joints. Given the critical role of T cells in the pathology of RA, the regulatory functions of DNA methylation in T cell biology remain unclear. In this review, we elaborate on the relationship between RA pathogenesis and DNA methylation in the context of different T cell populations. We summarize the relevant methylation events in T cell development, differentiation, and T cell-related genes in disease prediction and drug efficacy. Understanding the epigenetic regulation of T cells has the potential to profoundly translate preclinical results into clinical practice and provide a framework for the development of novel, individualized RA therapeutics.