Reciprocal inhibition of YAP/TAZ and NF-κB regulates osteoarthritic cartilage degradation

NF-κB Signaling Pathway in Rheumatoid Arthritis: Mechanisms and Therapeutic Potential

Rheumatoid arthritis (RA) is an autoimmune chronic inflammatory disease that imposes a heavy economic burden on patients and society. Bone and cartilage destruction is considered an important factor leading to RA, and inflammation, oxidative stress, and mitochondrial dysfunction are closely related to bone erosion and cartilage destruction in RA. Currently, there are limitations in the clinical treatment methods for RA, which urgently necessitates finding new effective treatments for patients. Nuclear transcription factor-κB (NF-κB) is a signaling transcription factor that is widely present in various cells. It plays an important role as a stress source in the cellular environment and regulates gene expression in processes such as immunity, inflammation, cell proliferation, and apoptosis. NF-κB has long been recognized as a pathogenic factor of RA, and its activation can exacerbate RA by promoting inflammation, oxidative stress, mitochondrial dysfunction, and bone destruction. Conversely, inhibiting the activity of the NF-κB pathway effectively inhibits these pathological processes, thereby alleviating RA. Therefore, NF-κB may be a potential therapeutic target for RA. This article describes the physiological structure of NF-κB and its important role in RA through the regulation of oxidative stress, inflammatory response, mitochondrial function, and bone destruction. Meanwhile, we also summarized the impact of NF-κB crosstalk with other signaling pathways on RA and the effect of related drugs or inhibitors targeting NF-κB on RA. The purpose of this article is to provide evidence for the role of NF-κB in RA and to emphasize its significant role in RA by elucidating the mechanisms, so as to provide a theoretical basis for targeting the NF-κB pathway as a treatment for RA.

The critical role of the Hippo signaling pathway in renal fibrosis

Renal fibrosis is a fundamental pathological change in the progression of various chronic kidney diseases to the end stage of renal disease. The Hippo signaling pathway is an evolutionary highly conserved signaling pathway that is involved in the regulation of organ size, tissue regeneration, and human reproduction and development. Currently, many studies have shown that it is closely associated with renal diseases, such as, renal fibrosis, diabetic nephropathy, and renal cancer. Here, we review the current researches on the effect of Hippo signaling pathway on renal fibrosis, which provides new ideas and theoretical basis for clinical therapeutics of renal fibrosis.

M2 Macrophage-Derived Extracellular Vehicles-Loaded Hyaluronic Acid-Alginate Hydrogel for Treatment of Osteoarthritis

OBJECTIVE

Osteoarthritis (OA), a high-prevalence degenerative cartilage disease, urgently requires novel therapeutic strategies. M2 macrophage-derived exosomes (M2-Exo) demonstrate therapeutic potential for OA, though their regulatory mechanisms in chondrocyte-macrophage (Mφ) interactions remain to be elucidated. To investigate the regulatory effects of M2-Exo on chondrocytes and Mφ in vitro, and to evaluate the therapeutic effect of the M2-Exo-loaded hydrogel system (ALG-M2Exo) on cartilage damage in a rat OA model.

METHODS

In the cell experiment, M2-Exo were extracted and characterized using ultracentrifugation. Different concentrations of M2-Exo were co-cultured with inflammatory chondrocytes or M1Mφ to evaluate their direct anti-inflammatory effects and the ability to promote M1Mφ repolarization to the M2 phenotype, using methods such as EdU, TUNEL, qRT-PCR, and Western blot. Then, the repolarized RM2Mφ were co-cultured with inflammatory chondrocytes to verify their anti-inflammatory efficacy, employing similar detection methods. In the in vivo experiment, sodium iodoacetate was injected to establish a rat knee OA model, followed by interventions including ALG-M2Exo. After 4 and 8 weeks, samples were collected for gross observation and histological staining to assess cartilage damage repair.

RESULTS

In the cell experiment, M2-Exo exhibited typical exosomal characteristics, directly promoting the proliferation of inflammatory chondrocytes, inhibiting their apoptosis, reducing the expression of TNF-α, iNOS, and MMP-13, and increasing the expression of IL-10 and COL II. RM2Mφ showed similar therapeutic effects on inflammatory chondrocytes as M2-Exo. In the in vivo experiment, the ALG-M2Exo group demonstrated superior repair effects on cartilage damage compared to other groups, with the treatment effect at 8 weeks being better than at 4 weeks.

CONCLUSION

ALG-M2Exo effectively promotes the repair of cartilage damage in OA through both a direct pathway by releasing M2-Exo that act on chondrocytes and an indirect pathway that facilitates the repolarization of M1Mφ to M2Mφ.

Therapeutic targets in aging-related osteoarthritis: A focus on the extracellular matrix homeostasis

Osteoarthritis (OA) represents a globally prevalent degenerative bone diseases and is the primary contributors to pain and disability among middle-aged and elderly people, thereby imposing significant social and economic burdens. When articular cartilage is in the aging environment, epigenetic modifications, DNA damage and mitochondrial dysfunction lead to cell senescence. Chondrocyte senescence has been identified as a pivotal event in this metabolic dysregulation of the extracellular matrix (ECM). It can affect the composition and structure of ECM, and the mechanical and biological signals transmitted by ECM to senescent chondrocytes affect their physiology and pathology. Over the past few decades, the role of ECM in aging-related OA has received increasing attention. In this review, we summarize the changes of cartilage's major ECM (type II collagen and aggrecan) and the interaction between aging and ECM in OA, and explore therapeutic strategies targeting cartilagae ECM, such as noncoding RNAs, small-molecule drugs, and mesenchymal stem cell (MSC)-derived extracellular vesicles for OA. The aim of this study was to elucidate the potential benefits of ECM-based therapies as novel strategies for the management of OA diseases.

The Hippo pathway in bone and cartilage: implications for development and disease

Bone is the main structure of the human body; it mainly plays a supporting role and participates in metabolic processes. The Hippo signaling pathway is composed of a series of protein kinases, including the mammalian STE20-like kinase MST1/2 and the large tumor suppressor LATS1/2, which are widely involved in pathophysiological processes, including cell proliferation, differentiation, apoptosis and death, especially those related to biomechanical transduction in vivo. However, the role of it in regulating skeletal system development and the evolution of bone-related diseases remains poorly understood. The pathway can intervene in and regulate the physiological activities of bone-related cells such as osteoclasts and chondrocytes through its own or other bone-related signaling pathways, such as the Wnt pathway, the Notch pathway, and receptor activator of nuclear factor-κB ligand (RANKL), thereby affecting the occurrence and development of bone diseases. This article discusses the role of the Hippo signaling pathway in bone development and disease to provide new insights into the treatment of bone-related diseases by targeting the Hippo signaling pathway.

M-Motif, a potential non-conventional NLS in YAP/TAZ and other cellular and viral proteins that inhibits classic protein import

Multiple mechanisms were proposed to mediate the nuclear import of TAZ/YAP, transcriptional co-activators regulating organ growth and regeneration. Our earlier observations showed that TAZ/YAP harbor a C-terminal, unconventional nuclear localization signal (NLS). Here, we show that this sequence, necessary and sufficient for basal, ATP-independent nuclear import, contains an indispensable central methionine flanked by negatively charged residues. Based on these features, we define the M-motif and propose that it is a new class of NLS, also present and import-competent in other cellular (STAT1 and cyclin B1) and viral (ORF6 of SARS-CoV2, VSV-M) proteins. Accordingly, ORF6 SARS-Cov2 competitively inhibits TAZ/YAP uptake, while TAZ abrogates STAT1 import. Similar to viral M-motif proteins, TAZ binds RAE1 and inhibits classic nuclear protein import, including that of antiviral factors (IRF3 and NF-κB). However, RAE1 is dispensable for TAZ import itself. Thus, the TAZ/YAP NLS has a dual function: it mediates unconventional nuclear import and inhibits classic import, contributing to the suppression of antiviral responses.

Acupotomy Ameliorates KOA Related Chondrocyte Premature Senescence Through YAP/FOXD1 Pathway

Purpose

Premature senescence of chondrocytes is a typical lesion of knee osteoarthritis (KOA). Abnormal cartilage stress can inhibit the mechanosensitive Yes-associated protein (YAP) / transcription factor forkhead box D1 (FOXD1) pathway, which is related to premature senescence of chondrocytes, thereby accelerating the progression of the lesion. This study aims to investigate whether acupotomy intervention could inhibit the premature senescence of chondrocytes and protect the cartilage of KOA rabbits.

Methods

18 male New Zealand rabbits were randomly divided into 3 groups (n = 6 each): control, KOA, and KOA + acupotomy (KOA+Apo). KOA, KOA+Apo rabbits were modeled by modified Videman's method for 6 weeks. After modeling, the KOA+Apo groups were subjected to acupotomy once a week for 3 weeks on the muscles around the left hind knee. The modified Lequesne MG score and passive range of motion (PROM) were used to evaluate the general condition and exercise ability of rabbits. Cartilage degeneration was detected by safranin O-fast green staining and transmission electron microscope(TEM). Type II collagen (Col-II) and aggrecan by immunohistochemistry (IHC), IL-7 and MMP-13 by Enzyme-Linked Immunosorbent Assay (ELISA), and p53, Rb1, p - YAP, YAP, FOXD1 by IHC, Western blot, or RT - PCR.

Results

Acupotomy effectively curbed cartilage degeneration and chondrocyte premature senescence in KOA rabbits. Mechanistically, it cut IL - 7 and MMP-13 levels, easing the inflammatory milieu and extracellular matrix degradation. It also regulated p53 and Rb1, controlling cell - cycle progression. Crucially, acupotomy upregulated the YAP/FOXD1 pathway, which, by affecting downstream genes, modulated IL - 7, MMP-13, p53, and Rb1 levels, acting as a pivotal molecular link in its regulatory effects.

Conclusion

Acupotomy may protect KOA rabbits' cartilage by inhibiting chondrocytes premature senescence via the YAP/FOXD1 pathway, offering a new theoretical basis for treating mechanically - induced KOA.

The targeting of YAP by kaempferol regulates bone homeostasis and improves osteoporosis in rats

This study investigated the potential therapeutic effect of kaempferol on osteoporosis by regulating bone homeostasis through the YAP. The ovariectomy model was constructed. The changes in bone and liver tissue were observed through HE staining. Bone metabolism and inflammatory markers were quantitatively analyzed using RT-qPCR and ELISA. Changes in the YAP/NF-κB signaling pathway were detected through Western blot and immunofluorescence. In vitro, the activity and secretion levels of MC3 T3-E1-differentiated osteoblasts were assessed using CCK- 8 and ELISA. The effects of osteoblast-secreted factors on osteoclast-induced differentiation were analyzed using alizarin red staining, phalloidin staining, ELISA, TRAP staining, and SEM. Finally, the regulatory effects of kaempferol on the expression of bone homeostasis in osteoclasts were examined by immunofluorescence and Western blot. Kaempferol treatment improved trabecular bone structure, increased bone density, and modulated bone metabolism by enhancing OPG expression and suppressing TRAP, NFATC1, and RANKL levels. Kaempferol inhibited the activation of the NF-κB pathway and increased YAP expression, reducing inflammatory factors. In vitro, kaempferol promoted osteoblast differentiation and inhibited osteoclast activity. These effects were most pronounced at higher kaempferol doses and were associated with improved bone remodeling and reduced bone resorption. Kaempferol exhibits significant potential for osteoporosis treatment by regulating bone homeostasis, mitigating inflammation through modulating the YAP.

N6-Methyladenosine-Modified circSMAD4 Prevents Lumbar Instability Induced Cartilage Endplate Ossification

Lumbar instability causes cartilage endplate ossification and intervertebral disc degeneration. In this study, it is determined that circSMAD4, a Yap1-related circRNA, is stably downregulated under abnormal stress. In vitro, circSMAD4 knockdown resulted in Yap1 mRNA degradation, whereas circSMAD4 overexpression increased Yap1 mRNA expression and nuclear translocation. Hence, the stabilization of circSMAD4 is essential for maintaining the homeostasis of endplate cartilage under abnormal stress. Furthermore, transcriptome sequencing and mass spectrometry analysis revealed that METTL14-mediated N6-methyladenosine (m6A) modification can stabilize circSMAD4 expression. Moreover, circSMAD4 is shown to regulate Yap1 mRNA through the m6A reader IGF2BP1. The IGF2BP1 functions to translocate Yap1 mRNA into the nucleus, which protects endplate chondrocytes from degeneration. Finally, local injection of an AAV5-containing circSMAD4 overexpression plasmid successfully rescued LSI-induced cartilage endplate degeneration, which wasn't observed in Yap1 knockout mice. These findings suggest that m6A-modified circSMAD4 can stabilize Yap1 mRNA expression and translocation, thus preventing degeneration of the cartilage endplate under abnormal stress. Hence, circSMAD4 may become a potential therapeutic tool for managing instability-induced intervertebral disc degeneration.

4D Biofabrication of Magnetically Augmented Callus Assembloid Implants Enables Rapid Endochondral Ossification via Activation of Mechanosensitive Pathways

The use of magnetic-driven strategies for non-contact manipulation of engineered living modules opens up new possibilities for tissue engineering. The integration of magnetic nanoparticles (MNPs) with cartilaginous microtissues enables model-driven 4D bottom-up biofabrication of remotely actuated assembloids, providing unique properties to mechanoresponsive tissues, particularly skeletal constructs. However, for clinical use, the long-term effects of magnetic stimulation on phenotype and in vivo functionality need further exploration. Magnetic-driven biofabrication includes both rapid processes, such as guided microtissue assembly, and slower biological processes, like extracellular matrix secretion. This work explores the interplay between magnetic fields and MNP-loaded cartilaginous microtissues through mathematical modeling and experimental approaches, investigating long-term stimulation effects on ECM maturation and chondrogenic hypertrophy. Transcriptomic analysis reveal that magnetic stimulation activated mechanosensitive pathways and catabolic processes, driving accelerated cartilage-to-bone transitions via endochondral ossification, outcomes not observed in non-stimulated controls. This study paves the way for pre-programmed, remotely actuated skeletal assembloids with superior bone-forming capacity for regenerating challenging bone fractures.

Deciphering chondrocyte diversity in diabetic osteoarthritis through single-cell transcriptomics

The pathophysiological distinctions between osteoarthritis (OA) and diabetic osteoarthritis (DOA) are critical yet not well delineated. In this study, we employed single-cell RNA sequencing to clarify the unique cellular and molecular mechanisms underpinning the progression of both conditions. We identified a novel subpopulation of chondrocytes in DOA, termed 'Heat Shock' chondrocytes, marked by the expression of distinct molecular markers including HSPA1A, HSPA1B, HSPB1, and HSPA8. Our comprehensive gene expression analysis revealed a pronounced upregulation of inflammatory pathways associated with oxidative stress-namely the MAPK, NF-κB, and PI3K signaling pathways-in the effector and proliferating chondrocyte subpopulations, with a predominance in DOA. Further, our investigation into cell-cell communication demonstrated a significant diminution of intercellular signaling in DOA compared to OA. These insights not only elucidate distinct cellular heterogeneities and potential pathogenic mechanisms differentiating OA from DOA but also enhance our understanding of their molecular pathophysiology, offering novel avenues for targeted therapeutic strategies.

Cyclic compression loading alters osteoarthritis-related gene expression in three-dimensionally cultured human articular chondrocytes via a different mechanism than interleukin-1β induction

OBJECTIVES

Mechanical and inflammatory stimuli are key factors in the pathophysiology of osteoarthritis (OA). However, the effects of mechanical stimulation on joint tissues and cells at the molecular level and the mechanisms of interaction after stimulation with inflammatory cytokines remains uninvestigated.

METHODS

Three-dimensional cyclic compression loading (CCL) was applied to human articular chondrocytes, and the expression of OA-related genes was analyzed using reverse transcription quantitative real-time polymerase chain reaction. Additionally, the effects of CCL after the chondrocytes were stimulated with interleukin (IL)-1β were evaluated. A DNA microarray assay was used to compare changes in gene expression after chondrocytes were stimulated with IL-1β and CCL was applied, and to search for pathways that are affected by CCL.

RESULTS

CCL of 40 kPa significantly upregulated the expression of IL-8, cyclooxygenase (COX)-2, nerve growth factor, matrix metalloproteinase (MMP)-1, and MMP-3. Transcription of IL-8, COX-2, and MMP-3 was synergistically promoted by CCL and IL-1β. The top 10 pathways enriched in the Kyoto Encyclopedia of Genes and Genomes enrichment analysis of differentially expressed genes were not common in either group, except for the "cytokine-cytokine receptor interaction". The "tumor necrosis factor signaling pathway" and the "nuclear factor-kappa B signaling pathway" in the IL-1β group and "cell cycle" and the "Hippo signaling pathway" in the CCL group were included.

CONCLUSIONS

Comprehensive gene expression analysis revealed that CCL-induced changes in gene expression were different to those induced by stimulation with IL-1β. Our results provide new insights into the involvement of mechanical stimulation in the pathogenesis of OA.

Role of YAP/TAZ in bone diseases: A transductor from mechanics to biology

Wolff's Law and the Mechanostat Theory elucidate how bone tissues detect and convert mechanical stimuli into biological signals, crucial for maintaining bone equilibrium. Abnormal mechanics can lead to diseases such as osteoporosis, osteoarthritis, and nonunion fractures. However, the detailed molecular mechanisms by which mechanical cues are transformed into biological responses in bone remain underexplored. Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ), key regulators of bone homeostasis, are instrumental in this process. Emerging research highlights bone cells' ability to sense various mechanical stimuli and relay these signals intracellularly. YAP/TAZ are central in receiving these mechanical cues and converting them into signals that influence bone cell behavior. Abnormal YAP/TAZ activity is linked to several bone pathologies, positioning these proteins as promising targets for new treatments. Thus, this review aims to provide an in-depth examination of YAP/TAZ's critical role in the interpretation of mechanical stimuli to biological signals, with a special emphasis on their involvement in bone cell mechanosensing, mechanotransduction, and mechanoresponse. The translational potential of this article: Clinically, appropriate stress stimulation promotes fracture healing, while bed rest can lead to disuse osteoporosis and excessive stress can cause osteoarthritis or bone spurs. Recent advancements in the understanding of YAP/TAZ-mediated mechanobiological signal transduction in bone diseases have been significant, yet many aspects remain unknown. This systematic review summarizes current research progress, identifies unaddressed areas, and highlights potential future research directions. Advancements in this field facilitate a deeper understanding of the molecular mechanisms underlying bone mechanics regulation and underscore the potential of YAP/TAZ as therapeutic targets for bone diseases such as fractures, osteoporosis, and osteoarthritis.

Targeting CDK4/6 suppresses colorectal cancer by destabilizing YAP1

Colorectal cancer (CRC) is among the most prevalent and deadly cancers worldwide. The Yes-associated protein 1 (YAP1) is frequently dysregulated in cancers, contributing to cancer stemness, chemoresistance, and cancer-related death. However, strategies directly targeting YAP1 have not yet been successful because of the lack of active binding pockets and unregulated toxicity. In this study, our Food and Drug Administration (FDA)-approved drug screening reveals that abemaciclib, a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor, dramatically promotes the proteasome-dependent degradation of YAP1, thereby inhibiting tumor progression in CRC cells and patient-derived xenograft models. We further identify deubiquitinating enzyme 3 (DUB3) as the bona fide deubiquitinase of YAP1 in CRC. Mechanistically, CDK4/6 directly phosphorylates DUB3 at Ser41, activating DUB3 to deubiquitinate and stabilize YAP1. Conversely, loss of Ser41 phosphorylation by CDK4/6 inhibition or Ser41A mutation, promotes YAP1 degradation and suppresses YAP1-driven tumor progression. Histological analysis shows a positive correlation between DUB3 and YAP1 expression in CRC specimens. Collectively, our study uncovers a novel oncogenic role of the CDK4/6-DUB3 pathway, which promotes YAP1 stabilization and tumor-promoting function, highlighting that targeting CDK4/6 offers a potential therapeutic strategy for CRC with aberrantly upregulated DUB3 and YAP1.

Live-cell FRET assay on the stoichiometry and affinity of the YAP complexes in MCF-7 cells

Yes-associated protein (YAP), a focal point of current biological research, is involved in regulating various life processes. In this report, live-cell fluorescence resonance energy transfer (FRET) imaging was employed to unravel the YAP complexes in MCF-7 cells. Fluorescence imaging of living cells co-expressing CFP (cyan fluorescent protein)-YAP and YFP (yellow fluorescent protein)-LATS1 (large tumor suppressor 1) plasmids revealed that YAP promoted LATS1 oligomerization around mitochondria. Moreover, FRET two-hybrid assay showed that YAP directly interacted with LATS1 to form dimer. Similarly, we found that YAP directly interacted with large tumor suppressor 2 (LATS2) to form a heterotrimer with 1:2 in cytoplasm and around mitochondria. In addition, YAP directly interacted with angiomotin (AMOT) to form a heterodimer in cytoplasm. However, YAP did not interact with O-linked N-acetylglucosamine transferase (OGT). Furthermore, FRET assay also indicated that YAP exhibited a higher affinity with AMOT, followed by LATS1, and least with LATS2. In summary, YAP directly interacts with LATS1 and AMOT to form a heterodimer, with LATS2 to form a heterotrimer with 1:2, and shows a preference for binding to AMOT, followed by LATS1, and lastly LATS2, providing new insights into the Hippo-YAP signaling pathway.

The Role of Yes-Associated Protein in Inflammatory Diseases and Cancer

Yes-associated protein (YAP) plays a central role in the Hippo pathway, primarily governing cell proliferation, differentiation, and apoptosis. Its significance extends to tumorigenesis and inflammatory conditions, impacting disease initiation and progression. Given the increasing relevance of YAP in inflammatory disorders and cancer, this study aims to elucidate its pathological regulatory functions in these contexts. Specifically, we aim to investigate the involvement and molecular mechanisms of YAP in various inflammatory diseases and cancers. We particularly focus on how YAP activation, whether through Hippo-dependent or independent pathways, triggers the release of inflammation and inflammatory mediators in respiratory, cardiovascular, and digestive inflammatory conditions. In cancer, YAP not only promotes tumor cell proliferation and differentiation but also modulates the tumor immune microenvironment, thereby fostering tumor metastasis and progression. Additionally, we provide an overview of current YAP-targeted therapies. By emphasizing YAP's role in inflammatory diseases and cancer, this study aims to enhance our understanding of the protein's pivotal involvement in disease processes, elucidate the intricate pathological mechanisms of related diseases, and contribute to future drug development strategies targeting YAP.

Kat7 accelerates osteoarthritis disease progression through the TLR4/NF-κB signaling pathway

Osteoarthritis (OA) is a common degenerative bone and joint disease with an unclear pathogenesis. Our study identified that the histone acetyltransferase encoded by Kat7 is upregulated in the affected articular cartilage of OA patients and in a mice model of medial meniscal instability-induced OA. Chondrocyte-specific knockdown of Kat7 expression exhibited a protective effect on articular cartilage integrity. In vitro experiments demonstrated that KAT7 promotes cartilage catabolism, inhibits cartilage anabolism, and induces chondrocyte senescence and apoptosis. Conversely, knocking down Kat7 was shown to protect chondrocyte function. Corresponding in vivo results indicated that silencing Kat7 effectively enhances cartilage anabolism, prevents articular cartilage damage, and significantly slows OA progression. Mechanistically, KAT7 activates the TLR4/NF-κB signaling pathway, and inhibition of this pathway reverses the catabolic effects and restores anabolic activity in the presence of Kat7 overexpression. Collectively, these findings confirm the critical role of KAT7 in the pathogenesis of OA and suggest that Kat7 represents a potential therapeutic target for OA treatment. KEY MESSAGES: There is a lack of clinically effective drugs for the treatment of osteoarthritis (OA). Kat7 plays a key role in the development of OA. Knocking down Kat7 expression can alleviate the progression of OA. Kat7 accelerates the progression of OA by activating the TLR4/NF-KB signaling pathway.

A Baicalin-Based Functional Polymer in Dynamic Reversible Networks Alleviates Osteoarthritis by Cellular Interactions

Osteoarthritis (OA) is increasingly recognized as a whole-organ disease predominantly affecting the elderly, characterized by typical alterations in subchondral bone and cartilage, along with recurrent synovial inflammation. Despite the availability of various therapeutics and medications, a complete resolution of OA remains elusive. In this study, novel functional hydrogels are developed by integrating natural bioactive molecules for OA treatment. Specifically, baicalin (Bai) is combined with 2-hydroxyethyl acrylate (HEA) to form a polymerizable monomer (HEA-Bai) through esterification, which is subjected to reversible addition-fragmentation chain transfer (RAFT) polymerization to produce Bai-based polymer (Pm). These macromolecules are incorporated into Schiff-base hydrogels, which demonstrate excellent mechanical properties and self-healing performance. Notably, the Bai-based formulations are taken up by fibroblast-like synoviocytes (FLSs), where they regulate glycolysis. Mechanistically, inhibition of yes-associated protein 1 (YAP1) by the formulations suppressed the FLSs glycolysis and reduced the secretion of inflammatory factors, including interleukin 1β (IL-1β), IL-6, and IL-8. Furthermore, the functional hydrogel (AG-Pm)-OC, severing as a lubricant and nutrient, prolonged joint retention of Bai, thereby reducing cartilage degradation and synovial inflammation. Meanwhile, (AG-Pm)-OC alleviated joint pain by targeting the YAP1 signaling and inhibiting macrophage recruitment and polarization. Taken together, this flavonoid-based injectable hydrogel exhibits enhanced biocompatibility and efficacy against OA.

The role of HIF-1α in hypoxic metabolic reprogramming in osteoarthritis

The joint dysfunction caused by osteoarthritis (OA) is increasingly becoming a major challenge in global healthcare, and there is currently no effective strategy to prevent the progression of OA. Therefore, better elucidating the relevant mechanisms of OA occurrence and development will provide theoretical basis for formulating new prevention and control strategies. Due to long-term exposure of cartilage tissue to the hypoxic microenvironment of joints, metabolic reprogramming changes occur. Hypoxia-inducible factor-1alpha (HIF-1α), as a core gene regulating hypoxia response in vivo, plays an important regulatory role in the hypoxic metabolism of chondrocytes. HIF-1α adapts to the hypoxic microenvironment by regulating metabolic reprogramming changes such as glycolysis, oxidative phosphorylation (OXPHOS), amino acid metabolism, and lipid metabolism in OA chondrocytes. In addition, HIF-1α also regulates macrophage polarization and synovial inflammation, chondrocytes degeneration and extracellular matrix (ECM) degradation, subchondral bone remodeling and angiogenesis in the hypoxic microenvironment of OA, and affects the pathophysiological progression of OA. Consequently, the regulation of chondrocytes metabolic reprogramming by HIF-1α has become an important therapeutic target for OA. Therefore, this article reviews the mechanism of hypoxia affecting chondrocyte metabolic reprogramming, focusing on the regulatory mechanism of HIF-1α on chondrocyte metabolic reprogramming, and summarizes potential effective ingredients or targets targeting chondrocyte metabolic reprogramming, in order to provide more beneficial basis for the prevention and treatment of clinical OA and the development of effective drugs.

Mechanism of action and new developments in the study of curcumin in the treatment of osteoarthritis: a narrative review

Osteoarthritis is a degenerative joint disease that affects the aging population worldwide. It has an underlying inflammatory cause that leads to loss of chondrocytes, reducing the cartilage layer at the affected joints. Compounds with anti-inflammatory properties are potential therapeutic agents for osteoarthritis. Curcumin, derived from species of the Curcuma, is an anti-inflammatory compound. The purpose of this review is to summarize the anti-osteoarthritic effects of curcumin from clinical and preclinical studies. Many clinical trials have been conducted to determine curcumin's effectiveness in osteoarthritis patients. Available studies have shown that curcumin prevents chondrocyte apoptosis and inhibits the release of proteoglycans and metalloproteinases as well as the expression of cyclooxygenase, prostaglandin E-2, and inflammatory cytokines in chondrocytes. The mechanism of action of curcumin also involves multiple cell signaling pathways, including Nuclear factor kappa-B(NF-κB), Mitogen-activated protein kinase (MAPK), Wnt/β-catenin pathway (Wnt/β-catenin), The Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3), Nuclear factor erythroid 2-related factor 2/antioxidant response elements/heme oxygenase-1(Nrf2/ARE/HO-1), and Phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (PI3K/AKT/mTOR) signaling pathways. Curcumin further reduced the release of inflammatory factors and apoptosis by inhibiting the activation of NF-κB. In addition, curcumin modulates the MAPK, Nrf2/ARE/HO-1, and PI3K/Akt/mTOR signaling pathways and affects cell proliferation and apoptosis processes, a series of effects that together promote the healthy state of chondrocytes. In conclusion, curcumin, as a natural plant compound, exhibits significant anti-inflammatory potential by modulating inflammatory factors associated with articular osteoarthritis through multiple mechanisms. Its protective effects on articular cartilage and synovium make it a promising candidate for the treatment of OA. Future studies should further explore the mechanism of action of curcumin and its optimal dosage and therapeutic regimen in clinical applications, to provide more effective therapeutic options for osteoarthritis patients.

Rejuvenation of Bone Marrow Mesenchymal Stem Cells: Mechanisms and Their Application in Senile Osteoporosis Treatment

Bone marrow mesenchymal stromal cells (BM-MSCs) are multipotent cells present in bone marrow; they play a crucial role in the process of bone formation. Cellular senescence is defined as a stable state of cell cycle arrest that impairs the functioning of cells. Research has shown that aging triggers a state of senescence in BM-MSCs, leading to a reduced capacity for osteogenic differentiation and the accumulation of senescent cells, which can accelerate the onset of various diseases. Therefore, it is essential to explore mechanisms and strategies for the rejuvenation of senescent BM-MSCs. Senile osteoporosis (SOP) is a metabolic bone disease characterized by reduced bone formation. The senescence of BM-MSCs is considered one of the most important factors in the occurrence and development of SOP. Therefore, the rejuvenation of BM-MSCs for the treatment of SOP represents a promising strategy. This work provides a summary of the functional alterations observed in senescent BM-MSCs and a systematic review of the mechanisms that facilitate the rejuvenation of senescent BM-MSCs. Additionally, we analyze the progress in and the limitations associated with the application of rejuvenated senescent BM-MSCs to treat SOP, with the aim of providing new insights for the prevention and treatment of SOP.

The physiological and pathogenic roles of yes-associated protein/transcriptional co-activator with PDZ-binding motif in bone or skeletal motor system-related cells

Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) are the primary downstream effectors of the Hippo signaling pathway. This pathway plays a crucial role in regulating organ size, maintaining tissue homeostasis, and controlling cellular processes such as fate determination and tissue development. This review provides an overview of the current understanding of how the transcriptional regulators YAP and TAZ contribute to the physiological and pathological processes in tissues and cells associated with the skeletal motor system. The underlying molecular mechanisms and mechanical transduction were reviewed.

Regulation of senescence-associated secretory phenotypes in osteoarthritis by cytosolic UDP-GlcNAc retention and O-GlcNAcylation

UDP-GlcNAc serves as a building block for glycosaminoglycan (GAG) chains in cartilage proteoglycans and simultaneously acts as a substrate for O-GlcNAcylation. Here, we show that transporters for UDP-GlcNAc to the endoplasmic reticulum (ER) and Golgi are significantly downregulated in osteoarthritic cartilage, leading to increased cytosolic UDP-GlcNAc and O-GlcNAcylation in chondrocytes. Mechanistically, upregulated O-GlcNAcylation governs the senescence-associated secretory phenotype (SASP) by stabilizing GATA4 via O-GlcNAcylation at S406, which compromises its degradation by p62-mediated selective autophagy. Elevated O-GlcNAcylation in the superficial layer of osteoarthritic cartilage coincides with increased GATA4 levels. The topical deletion of Gata4 in this cartilage layer ameliorates post-traumatic osteoarthritis (OA) in mice while inhibiting O-GlcNAc transferase mitigates OA by decreasing GATA4 levels. Excessive glucosamine-induced O-GlcNAcylation stabilizes GATA4 in chondrocytes and exacerbates post-traumatic OA in mice. Our findings elucidate the role of UDP-GlcNAc compartmentalization in regulating secretory pathways associated with chronic joint inflammation, providing a senostatic strategy for the treatment of OA.

Identification of BCL3 as a biomarker for chondrocyte programmed cell death in osteoarthritis

Osteoarthritis (OA) is a condition that is widely prevalent and causes joint pain and disability, with programmed cell death (PCD) playing a role in its pathogenesis. This study aimed to identify biomarkers associated with PCD in OA and explore their potential roles. Three RNA-sequencing datasets (GSE114007, GSE51588 and GSE220243) related to OA were analysed. Differential expression and weighted gene co-expression network identified key differentially expressed PCD-related genes (DE-PRMGs). Potential biomarkers were identified and validated through receiver operating characteristic (ROC) curves, correlation analyses, gene set enrichment analysis, single-cell expression and RT-qPCR. A total of 45 DE-PRMGs were identified, affecting pathways like TNF signalling and RNA degradation. BCL3, TREM2 and NRP2 were prioritized as potential OA biomarkers, which are associated with ribosome function and immune cell infiltration and potentially linked to PCD. The functional role of one of the molecules identified, BCL3, was explored further using a cell model of inflammation induced chondrocytes. BCL3 was significantly down regulated in OA samples from the public dataset and clinical samples analysed by RT-qPCR. BCL3 overexpression reduced apoptosis in chondrocytes stimulated with inflammatory cytokines. Thus the functional studies highlighted the anti-apoptotic role of BCL3 in chondrocytes and provide new insights into OA pathogenesis with potential for future therapeutic development.

1,25(OH)2D3 induces chondrocyte autophagy and reduces the loss of proteoglycans in osteoarthritis through inhibiting the NF-κB pathway

OBJECTIVE

Nuclear transcription factor-κB (NF-κB) activation is a pivotal event in the pathogenesis of osteoarthritis (OA). OA patients frequently exhibit vitamin D (VD) deficiency, which is commonly associated with NF-κB activation. Our study aimed to investigate whether VD could protect against OA by modulating NF-κB pathway and to explore the underlying mechanisms.

METHODS

Proteins levels were assessed by western blot analysis, gene expression was quantified by quantitative real-time polymerase chain reaction (qRT‒PCR) in vivo and in vitro. The expression of phosphorylated-p65 (p-p65) in knee OA rats was detected by immunohistochemistry, and an NF-κB nuclear translocation assay was validated in chondrocytes. Immunoprecipitation was employed to detect the interaction between NF-κB and vitamin D receptor (VDR) in vivo and in vitro. Small interfering RNA (Si-NF-κB and Si-VDR) transfection was used to investigate the role of NF-κB and VDR signaling pathway in knee OA rats under VD influence. Cartilage changes were visualized of knee OA rats using hematoxylin and eosin as well as safranin-O/fast green of staining.

RESULTS

Our findings indicated that VD alleviates OA by inhibiting NF-κB pathway, which in turn reduces chondrocyte apoptosis and extracellular matrix (ECM) degradation. Further analysis revealed that VD primarily stabilizes NF-κB through the interaction of VDR and NF-κB, modulating the AMPK/mTOR signaling pathway to enhance autophagy and delay the progression of OA.

CONCLUSION

This study highlights the protective role of VD in OA by stabilization of NF-κB, mainly through the interaction between VDR and NF-κB. This interaction regulates the AMPK/mTOR signaling pathway, promoting autophagy and suggesting a potential therapeutic strategy for OA management. Key Points • VD confers a protective effect on OA by primarily stabilizing NF-κB through the interaction between VDR and NF-κB, which in turn inhibits NF-κB phosphorylation and nuclear translocation. • In chondrocytes, VD helps shield against OA by blocking NF-κB's entry into the nucleus, subsequently regulating autophagy via the AMPK/mTOR signaling pathway.

Targeting Chondrocyte Hypertrophy as Strategies for the Treatment of Osteoarthritis

Osteoarthritis (OA) is a common joint disease characterized by pain and functional impairment, which severely impacts the quality of life of middle-aged and elderly individuals. During normal bone development, chondrocyte hypertrophy is a natural physiological process. However, in the progression of OA, chondrocyte hypertrophy becomes one of its key pathological features. Although there is no definitive evidence to date confirming that chondrocyte hypertrophy is the direct cause of OA, substantial experimental data indicate that it plays an important role in the disease's pathogenesis. In this review, we first explore the mechanisms underlying chondrocyte hypertrophy in OA and offer new insights. We then propose strategies for inhibiting chondrocyte hypertrophy from the perspectives of targeting signaling pathways and tissue engineering, ultimately envisioning the future prospects of OA treatment.

Astrocytes phenomics as new druggable targets in healthy aging and Alzheimer's disease progression

For over a century after their discovery astrocytes were regarded merely as cells located among other brain cells to hold and give support to neurons. Astrocytes activation, "astrocytosis" or A1 functional state, was considered a detrimental mechanism against neuronal survival. Recently, the scientific view on astrocytes has changed. Accumulating evidence indicate that astrocytes are not homogeneous, but rather encompass heterogeneous subpopulations of cells that differ from each other in terms of transcriptomics, molecular signature, function and response in physiological and pathological conditions. In this review, we report and discuss the recent literature on the phenomic differences of astrocytes in health and their modifications in disease conditions, focusing mainly on the hippocampus, a region involved in learning and memory encoding, in the age-related memory impairments, and in Alzheimer's disease (AD) dementia. The morphological and functional heterogeneity of astrocytes in different brain regions may be related to their different housekeeping functions. Astrocytes that express diverse transcriptomics and phenomics are present in strictly correlated brain regions and they are likely responsible for interactions essential for the formation of the specialized neural circuits that drive complex behaviors. In the contiguous and interconnected hippocampal areas CA1 and CA3, astrocytes show different, finely regulated, and region-specific heterogeneity. Heterogeneous astrocytes have specific activities in the healthy brain, and respond differently to physiological or pathological stimuli, such as inflammaging present in normal brain aging or beta-amyloid-dependent neuroinflammation typical of AD. To become reactive, astrocytes undergo transcriptional, functional, and morphological changes that transform them into cells with different properties and functions. Alterations of astrocytes affect the neurovascular unit, the blood-brain barrier and reverberate to other brain cell populations, favoring or dysregulating their activities. It will be of great interest to understand whether the differential phenomics of astrocytes in health and disease can explain the diverse vulnerability of the hippocampal areas to aging or to different damaging insults, in order to find new astrocyte-targeted therapies that might prevent or treat neurodegenerative disorders.

The Hippo Signaling Pathway Manipulates Cellular Senescence

The Hippo pathway, a kinase cascade, coordinates with many intracellular signals and mediates the regulation of the activities of various downstream transcription factors and their coactivators to maintain homeostasis. Therefore, the aberrant activation of the Hippo pathway and its associated molecules imposes significant stress on tissues and cells, leading to cancer, immune disorders, and a number of diseases. Cellular senescence, the mechanism by which cells counteract stress, prevents cells from unnecessary damage and leads to sustained cell cycle arrest. It acts as a powerful defense mechanism against normal organ development and aging-related diseases. On the other hand, the accumulation of senescent cells without their proper removal contributes to the development or worsening of cancer and age-related diseases. A correlation was recently reported between the Hippo pathway and cellular senescence, which preserves tissue homeostasis. This review is the first to describe the close relationship between aging and the Hippo pathway, and provides insights into the mechanisms of aging and the development of age-related diseases. In addition, it describes advanced findings that may lead to the development of tissue regeneration therapies and drugs targeting rejuvenation.

Notoginsenoside R1-Protocatechuic aldehyde reduces vascular inflammation and calcification through increasing the release of nitric oxide to inhibit TGFβR1-YAP/TAZ pathway in vascular smooth muscle cells

Vascular calcification is a significant factor contributing to the rupture of vulnerable atherosclerotic plaques, ultimately leading to cardiovascular disease. However, no effective treatments are currently available to slow the progression of vascular calcification. Notoginsenoside R1 (R1) and protocatechuic aldehyde (PCAD), primary active components extracted from Panax notoginseng and Salvia miltiorrhiza Burge, have shown potential in mitigating endothelial injury and atherosclerosis. This study investigated the effects of R1-PCAD on nitric oxide (NO) production in endothelial cells (ECs) and its role in counteracting vascular calcification and inflammation. Additionally, it explored the mechanisms underlying these effects. To simulate atherosclerotic calcification, apolipoprotein E-deficient (ApoE-/-) mice were fed a high-fat diet and given intraperitoneal injections of vitamin D3. Treatment with the R1-PCAD combination improved endothelial function, reduced inflammation in the aorta, and lowered calcium deposition. Mechanistically, R1-PCAD enhanced eNOS-Ser1177 phosphorylation by activating the AMPKα/Akt pathway, which stimulated NO production and eNOS activation in ECs. In an in vitro co-culture model involving vascular smooth muscle cells (VSMCs) and ECs, R1-PCAD similarly reduced inflammation and calcification in VSMCs triggered by β-glycerophosphate, with these effects partially dependent on NO levels and EC functionality. Further investigation revealed that R1-PCAD facilitated NO release from ECs, which subsequently inhibited TGFβR1 activation in VSMCs. This inhibition reduced Smad2/3 activation and nuclear translocation of YAP/TAZ, thereby diminishing inflammation and calcification in VSMCs. These findings suggest that R1-PCAD alleviates vascular inflammation and calcification primarily via the NO-TGFβR1-YAP/TAZ signaling pathway. This study presents a promising new approach for treating vascular calcification by targeting intercellular signaling pathways.

Bimetallic clusterzymes-loaded dendritic mesoporous silica particle regulate arthritis microenvironment via ROS scavenging and YAP1 stabilization

Clusterzymes are synthetic enzymes exhibiting substantial catalytic activity and selectivity, which are uniquely driven by single-atom constructs. A dramatic increase in antioxidant capacity, 158 times more than natural trolox, is noted when single-atom copper is incorporated into gold-based clusterzymes to form Au24Cu1. Considering the inflammatory and mildly acidic microenvironment characteristic of osteoarthritis (OA), pH-dependent dendritic mesoporous silica nanoparticles (DMSNs) coupled with PEG have been employed as a delivery system for the spatial-temporal release of clusterzymes within active articular regions, thereby enhancing the duration of effectiveness. Nonetheless, achieving high therapeutic efficacy remains a significant challenge. Herein, we describe the construction of a Clusterzymes-DMSNs-PEG complex (CDP) which remarkably diminishes reactive oxygen species (ROS) and stabilizes the chondroprotective protein YAP by inhibiting the Hippo pathway. In the rabbit ACLT (anterior cruciate ligament transection) model, the CDP complex demonstrated inhibition of matrix metalloproteinase activity, preservation of type II collagen and aggregation protein secretion, thus prolonging the clusterzymes' protective influence on joint cartilage structure. Our research underscores the efficacy of the CDP complex in ROS-scavenging, enabled by the release of clusterzymes in response to an inflammatory and slightly acidic environment, leading to the obstruction of the Hippo pathway and downstream NF-κB signaling pathway. This study illuminates the design, composition, and use of DMSNs and clusterzymes in biomedicine, thus charting a promising course for the development of novel therapeutic strategies in alleviating OA.

Hippo Signaling Pathway Involvement in Osteopotential Regulation of Murine Bone Marrow Cells Under Simulated Microgravity

The development of osteopenia is one of the most noticeable manifestations of the adverse effects of space factors on crew members. The Hippo signaling pathway has been shown to play a central role in regulating the functional activity of cells through their response to mechanical stimuli. In the present study, the components of the Hippo pathway and the protective properties of osteodifferentiation inducers were investigated under simulated microgravity (smg) using a heterotypic bone marrow cell culture model, which allows for the maintenance of the close interaction between the stromal and hematopoietic compartments, present in vivo and of great importance for both the fate of osteoprogenitors and hematopoiesis. After 14 days of smg, the osteopotential and osteodifferentiation of bone marrow stromal progenitor cells, the expression of Hippo cascade genes and the immunocytochemical status of the adherent fraction of bone marrow cells, as well as the paracrine profile in the conditioned medium and the localization of Yap1 and Runx2 in mechanosensitive cells of the bone marrow were obtained. Simulated microgravity negatively affects stromal and hematopoietic cells when interacting in a heterotypic murine bone marrow cell culture. This is evidenced by the decrease in cell proliferation and osteopotential. Changes in the production of pleiotropic cytokines IL-6, GROβ and MCP-1 were revealed. Fourteen days of simulated microgravity induced a decrease in the nuclear translocation of Yap1 and the transcription factor Runx2 in the stromal cells of the intact group. Exposure to osteogenic induction conditions partially compensated for the negative effect of simulated microgravity. The data obtained will be crucial for understanding the effects of spaceflight on osteoprogenitor cell growth and differentiation via Hippo-Yap signaling.

IL-32 aggravates metabolic disturbance in human nucleus pulposus cells by activating FAT4-mediated Hippo/YAP signaling

Extracellular matrix (ECM) metabolism disorders in the inflammatory microenvironment play a key role in the pathogenesis of intervertebral disc degeneration (IDD). Interleukin-32 (IL-32) has been reported to be involved in the progression of various inflammatory diseases; however, it remains unclear whether it participates in the matrix metabolism of nucleus pulposus (NP) cells. Therefore, this study aimed to investigate the mechanism of IL-32 on regulating the ECM metabolism in the inflammatory microenvironment. RNA-seq was used to identify aberrantly expressed genes in NP cells in the inflammatory microenvironment. Western blotting, real-time quantitative PCR, immunohistochemistry and immunofluorescence analysis were performed to measure the expression of IL-32 and metabolic markers in human NP tissues or NP cells treated with or without tumor necrosis factor-α (TNF-α). In vivo, an adeno-associated virus overexpressing IL-32 was injected into the caudal intervertebral discs of rats to assess its effect on IDD. Proteins interacting with IL-32 were identified via immunoprecipitation and mass spectrometry. Lentivirus overexpressing IL-32 or knocking down Fat atypical cadherin 4 (FAT4), yes-associated protein (YAP) inhibitor-Verteporfin (VP) were used to treat human NP cells, to explore the pathogenesis of IL-32. Hippo/YAP signaling activity was verified in human NP tissues. IL-32 expression was significantly upregulated in degenerative NP tissues, as indicated in the clinical samples. Furthermore, IL-32 was remarkably overexpressed in TNF-α-induced degenerative NP cells. IL-32 overexpression induced IDD progression in the rat model. Mechanistically, the elevation of IL-32 in the inflammatory microenvironment enhanced its interactions with FAT4 and mammalian sterile 20-like kinase1/2 (MST1/2) proteins, prompting MST1/2 phosphorylation, and activating the Hippo/YAP signaling pathway, causing matrix metabolism disorder in NP cells. Our results suggest that IL-32 mediates matrix metabolism disorders in NP cells in the inflammatory micro-environment via the FAT4/MST/YAP axis, providing a theoretical basis for the precise treatment of IDD.

CD73 alleviates osteoarthritis by maintaining anabolism and suppressing catabolism of chondrocytes extracellular matrix

Background

Osteoarthritis (OA) is the most common degenerative joint disease, with articular cartilage degeneration as primary manifestation. Intra-articular injection of exogenous liposomal adenosine in mice knee has been shown to alleviate OA progression. However, the role of CD73, the rate-limiting enzyme of extracellular adenosine synthesis, in OA is still unknown.

Methods

In this work, we explored the expression changes of adenosine-related molecules via bioinformatic analysis. In addition, the expression level of these molecules was detected in OA cartilage. We also conducted a case-control study to investigate the genetic variants of selected SNPs on genes encoded adenosine-related molecules. To further explore the function of CD73 in chondrocytes, we knocked down the expression of CD73 with small interfering RNA and overexpressed CD73 with the use of lentivirus, and detected the expression of markers for anabolism and catabolism in mouse primary chondrocytes with or without IL-1β treatment. We also conducted in vivo experiments to explore the role of CD73 in OA.

Results

We found that the expression of CD73 was upregulated in OA, and the variants of SNP rs2229523 (base A to G) on NT5E (the encoding gene of CD73) were significantly higher in OA population, which might cause the amino acid encoded by this SNP change from threonine to alanine. The original helix structure in the adjacent region of amino acid encoded by SNP rs2229523 would be deconstructed after its mutation. Furthermore, we found that CD73 promoting the expression of Col2a1 but suppressing the expression of Mmp13 expression in mouse primary chondrocytes under inflammatory environment. The overexpression of CD73 attenuated bone remodeling and alleviated cartilage degeneration in DMM mice. Moreover, the physical activities were also improved in DMM mice overexpressed CD73 with the use of adeno-associated virus.

Conclusions

The variants of SNP rs2229523 (base A to G) on NT5E were significantly higher in OA population, and CD73 could alleviate OA by maintaining anabolism and suppressing catabolism of chondrocytes extracellular matrix.

The Translational Potential of this Article

This work showed that CD73 might be one of the biological therapeutic targets of OA, which would provide a reference for future novel treatment strategy of OA.

Emerging role and function of Hippo-YAP/TAZ signaling pathway in musculoskeletal disorders

Hippo pathway is an evolutionarily conservative key pathway that regulates organ size and tissue regeneration by regulating cell proliferation, differentiation and apoptosis. Yes-associated protein 1 (YAP)/ WW domain-containing transcription regulator 1 (TAZ) serves as a pivotal transcription factor within the Hippo signaling pathway, which undergoes negative regulation by the Hippo pathway. The expression of YAP/TAZ affects various biological processes, including differentiation of osteoblasts (OB) and osteoclasts (OC), cartilage homeostasis, skeletal muscle development, regeneration and quality maintenance. At the same time, the dysregulation of the Hippo pathway can concurrently contribute to the development of various musculoskeletal disorders, including bone tumors, osteoporosis (OP), osteoarthritis (OA), intervertebral disc degeneration (IDD), muscular dystrophy, and rhabdomyosarcoma (RMS). Therefore, targeting the Hippo pathway has emerged as a promising therapeutic strategy for the treatment of musculoskeletal disorders. The focus of this review is to elucidate the mechanisms by which the Hippo pathway maintains homeostasis in bone, cartilage, and skeletal muscle, while also providing a comprehensive summary of the pivotal role played by core components of this pathway in musculoskeletal diseases. The efficacy and feasibility of Hippo pathway-related drugs for targeted therapy of musculoskeletal diseases are also discussed in our study. These endeavors offer novel insights into the application of Hippo signaling in musculoskeletal disorders, providing effective therapeutic targets and potential drug candidates for treating such conditions.

Battling pain from osteoarthritis: causing novel cell death

Osteoarthritis (OA) is a significant contributor to pain and disability worldwide. Pain is the main complaint of OA patients attending the clinic and has a large impact on their quality of life and economic standards. However, existing treatments for OA-related pain have not been shown to achieve good relief. The main focus is on preventing and slowing the progression of OA so that the problem of OA pain can be resolved. Pain caused by OA is complex, with the nature, location, duration, and intensity of pain changing as the disease progresses. Previous research has highlighted the role of various forms of cell death, such as apoptosis and necrosis, in the progression of pain in OA. Emerging studies have identified additional forms of novel cell death, such as pyroptosis, ferroptosis, and necroptosis that are linked to pain in OA. Different types of cell death contribute to tissue damage in OA by impacting inflammatory responses, reactive oxygen species (ROS) production, and calcium ion levels, ultimately leading to the development of pain. Evidence suggests that targeting novel types of cell death could help alleviate pain in OA patients. This review delves into the complex mechanisms of OA pain, explores the relationship between different modes of novel cell death and pain, and proposes novel cell death as a viable strategy for the treatment of these conditions, with the goal of providing scientific references for the development of future OA pain treatments and drugs.

The Hippo signalling pathway in bone homeostasis: Under the regulation of mechanics and aging

The Hippo signalling pathway is a conserved kinase cascade that orchestrates diverse cellular processes, such as proliferation, apoptosis, lineage commitment and stemness. With the onset of society ages, research on skeletal aging-mechanics-bone homeostasis has exploded. In recent years, aging and mechanical force in the skeletal system have gained groundbreaking research progress. Under the regulation of mechanics and aging, the Hippo signalling pathway has a crucial role in the development and homeostasis of bone. We synthesize the current knowledge on the role of the Hippo signalling pathway, particularly its downstream effectors yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), in bone homeostasis. We discuss the regulation of the lineage specification and function of different skeletal cell types by the Hippo signalling pathway. The interactions of the Hippo signalling pathway with other pathways, such as Wnt, transforming growth factor beta and nuclear factor kappa-B, are also mentioned because of their importance for modulating bone homeostasis. Furthermore, YAP/TAZ have been extensively studied as mechanotransducers. Due to space limitations, we focus on reviewing how mechanical forces and aging influence cell fate, communications and homeostasis through a dysregulated Hippo signalling pathway.

Interplay of Glucose Metabolism and Hippo Pathway in Chondrocytes: Pathophysiology and Therapeutic Targets

In this review, we explore the intricate relationship between glucose metabolism and mechanotransduction pathways, with a specific focus on the role of the Hippo signaling pathway in chondrocyte pathophysiology. Glucose metabolism is a vital element in maintaining proper chondrocyte function, but it has also been implicated in the pathogenesis of osteoarthritis (OA) via the induction of pro-inflammatory signaling pathways and the establishment of an intracellular environment conducive to OA. Alternatively, mechanotransduction pathways such as the Hippo pathway possess the capacity to respond to mechanical stimuli and have an integral role in maintaining chondrocyte homeostasis. However, these mechanotransduction pathways can be dysregulated and potentially contribute to the progression of OA. We discussed how alterations in glucose levels may modulate the Hippo pathway components via a variety of mechanisms. Characterizing the interaction between glucose metabolism and the Hippo pathway highlights the necessity of balancing both metabolic and mechanical signaling to maintain chondrocyte health and optimal functionality. Furthermore, this review demonstrates the scarcity of the literature on the relationship between glucose metabolism and mechanotransduction and provides a summary of current research dedicated to this specific area of study. Ultimately, increased research into this topic may elucidate novel mechanisms and relationships integrating mechanotransduction and glucose metabolism. Through this review we hope to inspire future research into this topic to develop innovative treatments for addressing the clinical challenges of OA.

Matrix Viscoelasticity Tunes the Mechanobiological Behavior of Chondrocytes

In articular cartilage, the pericellular matrix acting as a specialized mechanical microenvironment modulates environmental signals to chondrocytes through mechanotransduction. Matrix viscoelastic alterations during cartilage development and osteoarthritis (OA) degeneration play an important role in regulating chondrocyte fate and cartilage matrix homeostasis. In recent years, scientists are gradually realizing the importance of matrix viscoelasticity in regulating chondrocyte function and phenotype. Notably, this is an emerging field, and this review summarizes the existing literatures to the best of our knowledge. This review provides an overview of the viscoelastic properties of hydrogels and the role of matrix viscoelasticity in directing chondrocyte behavior. In this review, we elaborated the mechanotransuction mechanisms by which cells sense and respond to the viscoelastic environment and also discussed the underlying signaling pathways. Moreover, emerging insights into the role of matrix viscoelasticity in regulating chondrocyte function and cartilage formation shed light into designing cell-instructive biomaterial. We also describe the potential use of viscoelastic biomaterials in cartilage tissue engineering and regenerative medicine. Future perspectives on mechanobiological comprehension of the viscoelastic behaviors involved in tissue homeostasis, cellular responses, and biomaterial design are highlighted. Finally, this review also highlights recent strategies utilizing viscoelastic hydrogels for designing cartilage-on-a-chip.

METTL3 regulates cartilage development and homeostasis by affecting Lats1 mRNA stability in an m6A-YTHDF2-dependent manner

Cartilage maintains the structure and function of joints, with disturbances leading to potential osteoarthritis. N6-methyladenosine (m6A), the most widespread post-transcriptional modification in eukaryotes, plays a crucial role in regulating biological processes. While current research has indicated that m6A affects the progression of osteoarthritis, its function in the development and homeostasis of articular cartilage remains unclear. Here we report that Mettl3 deficiency in chondrocytes leads to mandibular condylar cartilage morphological alterations, early temporomandibular joint osteoarthritis, and diminished adaptive response to abnormal mechanical stimuli. Mechanistically, METTL3 modulates Lats1 mRNA methylation and facilitates its degradation in an m6A-YTHDF2-dependent manner, which subsequently influences the degradation and nuclear translocation of YAP1. Intervention with the Hippo pathway inhibitor XMU-MP-1 alleviates condylar abnormality caused by Mettl3 knockout. Our findings demonstrate the role of METTL3 in cartilage development and homeostasis, offering insights into potential treatment strategies for osteoarthritis.

Breaking the Cycle: Matrix Metalloproteinase Inhibitors as an Alternative Approach in Managing Tuberculosis Pathogenesis and Progression

Mycobacterium tuberculosis (Mtb) has long posed a significant challenge to global public health, resulting in approximately 1.6 million deaths annually. Pulmonary tuberculosis (TB) instigated by Mtb is characterized by extensive lung tissue damage, leading to lesions and dissemination within the tissue matrix. Matrix metalloproteinases (MMPs) exhibit endopeptidase activity, contributing to inflammatory tissue damage and, consequently, morbidity and mortality in TB patients. MMP activities in TB are intricately regulated by various components, including cytokines, chemokines, cell receptors, and growth factors, through intracellular signaling pathways. Primarily, Mtb-infected macrophages induce MMP expression, disrupting the balance between MMPs and tissue inhibitors of metalloproteinases (TIMPs), thereby impairing extracellular matrix (ECM) deposition in the lungs. Recent research underscores the significance of immunomodulatory factors in MMP secretion and granuloma formation during Mtb pathogenesis. Several studies have investigated both the activation and inhibition of MMPs using endogenous MMP inhibitors (i.e., TIMPs) and synthetic inhibitors. However, despite their promising pharmacological potential, few MMP inhibitors have been explored for TB treatment as host-directed therapy. Scientists are exploring novel strategies to enhance TB therapeutic regimens by suppressing MMP activity to mitigate Mtb-associated matrix destruction and reduce TB induced lung inflammation. These strategies include the use of MMP inhibitor molecules alone or in combination with anti-TB drugs. Additionally, there is growing interest in developing novel formulations containing MMP inhibitors or MMP-responsive drug delivery systems to suppress MMPs and release drugs at specific target sites. This review summarizes MMPs' expression and regulation in TB, their role in immune response, and the potential of MMP inhibitors as effective therapeutic targets to alleviate TB immunopathology.

New Insights on the Therapeutic Potential of Runt-Related Transcription Factor 2 for Osteoarthritis: Evidence from Mendelian Randomization

INTRODUCTION

Research has highlighted the role of runt-related transcription factor 2 (Runx2) in the development of osteoarthritis (OA); however, its causal association remains unclear. This study aimed to explore whether Runx2 expression is causally associated with OA and assess its therapeutic potential for OA.

METHODS

Genetic proxy instruments for Runx2 expression were obtained from gene expression quantitative trait locus (eQTLs) study of eQTLGen Consortium (n = 31,684). Aggregated genome-wide association study (GWAS) data for OA (including all OA [177,517 cases and 649,173 controls], knee OA (KOA) [62,497 cases and 333,557 controls], and hip OA (HOA) [36,445 cases and 316,943 controls]) were extracted from the Genetics of Osteoarthritis Consortium. We integrated eQTLs data with OA GWAS data to estimate their causal association and to estimate the potential of Runx2 as a drug target in the treatment of OA using summary data-based Mendelian randomization (SMR) analysis. Furthermore, different OA GWAS data (including all OA [77,052 cases and 378,169 controls], KOA [24,955 cases and 378,169 controls], and HOA [15,704 cases and 378,169 controls]) derived from the GWAS Catalog database were used for replication study.

RESULTS

SMR analysis showed that high expression levels of Runx2 were associated with an increased risk of all OA [odds ratio (OR) 1.044, 95% confidence interval (CI) 1.023-1.067; P = 5.03 × 10-5], KOA (OR 1.040, 95% CI 1.006-1.075; P = 0.021), and HOA (OR 1.067, 95% CI 1.022-1.113; P = 0.003). This suggests that Runx2 inhibitors may have promising potential for the treatment of OA. Notably, the causal effects of Runx2 with all OA (OR 1.053, 95% CI 1.027-1.079; P = 3.95 × 10-5) and KOA (OR 1.043, 95% CI 1.001-1.087; P = 0.045) were repeated in the replication study, but limited evidence supported the association of Runx2 expression levels with HOA (OR 1.045, 95% CI 0.993-1.101; P = 0.094).

CONCLUSIONS

Our analyses indicate a positive correlation between Runx2 expression and OA risk across all three phenotypes, suggesting the potential of Runx2 inhibitors in the treatment of OA and providing evidence from a genetic perspective.

Gubi decoction mitigates knee osteoarthritis via promoting chondrocyte autophagy through METTL3-mediated ATG7 m6A methylation

Knee osteoarthritis (KOA) is a chronic joint disease that significantly affects the health of the elderly. As an herbal remedy, Gubi decoction (GBD) has been traditionally used for the treatment of osteoarthritis-related syndromes. However, the anti-KOA efficacy and mechanism of GBD remain unclear. This study aimed to experimentally investigate the anti-KOA efficacy and the underlying mechanism of GBD. The medial meniscus (DMM) mice model and IL-1β-stimulated chondrocytes were, respectively, constructed as in vivo and in vitro models of KOA to evaluate the osteoprotective effect and molecular mechanism of GBD. The UPLC-MS/MS analysis showed that GBD mainly contained pinoresinol diglucoside, rehmannioside D, hesperidin, liquiritin, baohuoside I, glycyrrhizic acid, kaempferol and tangeretin. Animal experiment showed that GBD could alleviate articular cartilage destruction and recover histopathological alterations in DMM mice. In addition, GBD inhibited chondrocyte apoptosis and restored DMM-induced dysregulated autophagy evidenced by the upregulation of ATG7 and LC3 II/LC3 I but decreased P62 level. Mechanistically, METTL3-mediated m6A modification decreased the expression of ATG7 in DMM mice, as it could be significantly attenuated by GBD. METTL3 overexpression significantly counteracted the protective effect of GBD on chondrocyte autophagy. Further research showed that GBD promoted proteasome-mediated ubiquitination degradation of METLL3. Our findings suggest that GBD could act as a protective agent against KOA. The protective effect of GBD may result from its promotion on chondrocyte autophagy by suppressing METTL3-dependent ATG7 m6A methylation.

Critical signaling molecules in the temporomandibular joint osteoarthritis under different magnitudes of mechanical stimulation

The mechanical stress environment in the temporomandibular joint (TMJ) is constantly changing due to daily mandibular movements. Therefore, TMJ tissues, such as condylar cartilage, the synovial membrane and discs, are influenced by different magnitudes of mechanical stimulation. Moderate mechanical stimulation is beneficial for maintaining homeostasis, whereas abnormal mechanical stimulation leads to degeneration and ultimately contributes to the development of temporomandibular joint osteoarthritis (TMJOA), which involves changes in critical signaling molecules. Under abnormal mechanical stimulation, compensatory molecules may prevent degenerative changes while decompensatory molecules aggravate. In this review, we summarize the critical signaling molecules that are stimulated by moderate or abnormal mechanical loading in TMJ tissues, mainly in condylar cartilage. Furthermore, we classify abnormal mechanical stimulation-induced molecules into compensatory or decompensatory molecules. Our aim is to understand the pathophysiological mechanism of TMJ dysfunction more deeply in the ever-changing mechanical environment, and then provide new ideas for discovering effective diagnostic and therapeutic targets in TMJOA.

Periodic Lamellae-Based Nanofibers for Precise Immunomodulation to Treat Inflammatory Bone Loss in Periodontitis

Periodontitis is a common oral disease accompanied by inflammatory bone loss. The pathological characteristics of periodontitis usually accompany an imbalance in the periodontal immune microenvironment, leading to difficulty in bone regeneration. Therefore, effective treatment strategies are needed to modulate the immune environment in order to treat periodontitis. Here, highly-oriented periodic lamellae poly(ε-caprolactone) electrospun nanofibers (PLN) are developed by surface-directed epitaxial crystallization. The in vitro result shows that the PLN can precisely modulate macrophage polarization toward the M2 phenotype. Macrophages polarized by PLN significantly enhance the migration and osteogenic differentiation of Bone marrow stromal cells. Notably, results suggest that the topographical cues presented by PLN can modulate macrophage polarization by activating YAP, which reciprocally inhibits the NF-κB signaling pathway. The in vivo results indicate that PLN can inhibit inflammatory bone loss and facilitate bone regeneration in periodontitis. The authors' findings suggest that topographical nanofibers with periodic lamellae is a promising strategy for modulating immune environment to treat inflammatory bone loss in periodontitis.

TAZ reverses the inhibitory effects of LPS on the osteogenic differentiation of human periodontal ligament stem cells through the NF-κB signaling pathway

BACKGROUND

Human periodontal ligament stem cells (hPDLSCs) are important candidate seed cells for periodontal tissue engineering, but the presence of lipopolysaccharide(LPS) in periodontal tissues inhibits the self-renewal and osteogenic differentiation of hPDLSCs. Our previous studies demonstrated that TAZ is a positive regulator of osteogenic differentiation of hPDLSCs, but whether TAZ can protect hPDLSCs from LPS is still unknown. The present study aimed to explore the regulatory effect of TAZ on the osteogenic differentiation of hPDLSCs in an LPS-induced inflammatory model, and to preliminarily reveal the molecular mechanisms related to the NF-κB signaling pathway.

METHODS

LPS was added to the culture medium of hPDLSCs. The influence of LPS on hPDLSC proliferation was analyzed by CCK-8 assays. The effects of LPS on hPDLSC osteogenic differentiation were detected by Alizarin Red staining, ALP staining, Western Blot and qRT-PCR analysis of osteogenesis-related genes. The effects of LPS on the osteogenic differentiation of hPDLSCs with TAZ overexpressed or knocked down via lentivirus were analyzed. NF-κB signaling in hPDLSCs was analyzed by Western Blot and immunofluorescence.

RESULTS

LPS inhibited the osteogenic differentiation of hPDLSCs, inhibited TAZ expression, and activated the NF-κB signaling pathway. Overexpressing TAZ in hPDLSCs partly reversed the negative effects of LPS on osteogenic differentiation and inhibited the activation of the NF-κB pathway by LPS. TAZ knockdown enhanced the inhibitory effects of LPS on osteogenesis.

CONCLUSION

Overexpressing TAZ could partly reverse the inhibitory effects of LPS on the osteogenic differentiation of hPDLSCs, possibly through inhibiting the NF-κB signaling pathway. TAZ is a potential target for improving hPDLSC-based periodontal tissue regeneration in inflammatory environments.

Hippo-PKCζ-NFκB signaling axis: A druggable modulator of chondrocyte responses to mechanical stress

Recent studies have implicated a crucial role of Hippo signaling in cell fate determination by biomechanical signals. Here we show that mechanical loading triggers the activation of a Hippo-PKCζ-NFκB pathway in chondrocytes, resulting in the expression of NFκB target genes associated with inflammation and matrix degradation. Mechanistically, mechanical loading activates an atypical PKC, PKCζ, which phosphorylates NFκB p65 at Serine 536, stimulating its transcriptional activation. This mechanosensitive activation of PKCζ and NFκB p65 is impeded in cells with gene deletion or chemical inhibition of Hippo core kinases LATS1/2, signifying an essential role of Hippo signaling in this mechanotransduction. A PKC inhibitor AEB-071 or PKCζ knockdown prevents p65 Serine 536 phosphorylation. Our study uncovers that the interplay of the Hippo signaling, PKCζ, and NFκB in response to mechanical loading serves as a therapeutic target for knee osteoarthritis and other conditions resulting from mechanical overloading or Hippo signaling deficiencies.

YAP promotes the early development of temporomandibular joint bony ankylosis by regulating mesenchymal stem cell function

To explore the role of YAP, a key effector of the Hippo pathway, in temporomandibular joint (TMJ) ankylosis. The temporal and spatial expression of YAP was detected via immunohistochemistry and multiplex immunohistochemistry on postoperative Days 1, 4, 7, 9, 11, 14 and 28 in a sheep model. Isolated mesenchymal stem cells (MSCs) from samples of the Day 14. The relative mRNA expression of YAP was examined before and after the osteogenic induction of MSCs. A YAP-silenced MSC model was constructed, and the effect of YAP knockdown on MSC function was examined. YAP is expressed in the nucleus of the key sites that determine the ankylosis formation, indicating that YAP is activated in a physiological state. The expression of YAP increased gradually over time. Moreover, the number of cells coexpressing of RUNX2 and YAP-with the osteogenic active zone labelled by RUNX2-tended to increase after Day 9. After the osteogenic induction of MSCs, the expression of YAP increased. After silencing YAP, the osteogenic, proliferative and migratory abilities of the MSCs were inhibited. YAP is involved in the early development of TMJ bony ankylosis. Inhibition of YAP using shRNA might be a promising way to prevent or treat TMJ ankylosis.

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.

MST1 knockdown inhibits osteoarthritis progression through Parkin-mediated mitophagy and Nrf2/NF-κB signalling pathway

Osteoarthritis (OA) is a complicated disease that involves apoptosis and mitophagy. MST1 is a pro-apoptotic factor. Hence, decreasing its expression plays an anti-apoptotic effect. This study aims to investigate the protective effect of MST1 inhibition on OA and the underlying processes. Immunofluorescence (IF) was used to detect MST1 expression in cartilage tissue. Western Blot, ELISA and IF were used to analyse the expression of inflammation, extracellular matrix (ECM) degradation, apoptosis and mitophagy-associated proteins. MST1 expression in chondrocytes was inhibited using siRNA and shRNA in vitro and in vivo. Haematoxylin-Eosin, Safranin O-Fast Green and alcian blue staining were used to evaluate the therapeutic effect of inhibiting MST1. This study discovered that the expression of MST1 was higher in OA patients. Inhibition of MST1 reduced inflammation, ECM degradation and apoptosis and enhanced mitophagy in vitro. MST1 inhibition slows OA progression in vivo. Inhibiting MST1 suppressed apoptosis, inflammation and ECM degradation via promoting Parkin-mediated mitophagy and the Nrf2-NF-κB axis. The results suggest that MST1 is a possible therapeutic target for the treatment of osteoarthritis as its inhibition delays the progression of OA through the Nrf2-NF-κB axis and mitophagy.