Tauroursodeoxycholic acid suppresses endoplasmic reticulum stress in the chondrocytes of patients with osteoarthritis

Spotlight on necroptosis: Role in pathogenesis and therapeutic potential of intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is the leading cause of low back pain, which is one of the major factors leading to disability and severe economic burden. Necroptosis is an important form of programmed cell death (PCD), a highly regulated caspase-independent type of cell death that is regulated by receptor-interacting protein kinase 1 (RIPK1), RIPK3 and mixed lineage kinase domain-like protein (MLKL)-mediated, play a key role in the pathophysiology of various inflammatory, infectious and degenerative diseases. Recent studies have shown that necroptosis plays an important role in the occurrence and development of IDD. In this review, we provide an overview of the initiation and execution of necroptosis and explore in depth its potential mechanisms of action in IDD. The analysis focuses on the connection between NP cell necroptosis and mitochondrial dysfunction-oxidative stress pathway, inflammation, endoplasmic reticulum stress, apoptosis, and autophagy. Finally, we evaluated the possibility of treating IDD by inhibiting necroptosis, and believed that targeting necroptosis may be a new strategy to alleviate the symptoms of IDD.

Insights into the underlying pathogenesis and therapeutic potential of endoplasmic reticulum stress in degenerative musculoskeletal diseases

Degenerative musculoskeletal diseases are structural and functional failures of the musculoskeletal system, including osteoarthritis, osteoporosis, intervertebral disc degeneration (IVDD), and sarcopenia. As the global population ages, degenerative musculoskeletal diseases are becoming more prevalent. However, the pathogenesis of degenerative musculoskeletal diseases is not fully understood. Previous studies have revealed that endoplasmic reticulum (ER) stress is a stress response that occurs when impairment of the protein folding capacity of the ER leads to the accumulation of misfolded or unfolded proteins in the ER, contributing to degenerative musculoskeletal diseases. By affecting cartilage degeneration, synovitis, meniscal lesion, subchondral bone remodeling of osteoarthritis, bone remodeling and angiogenesis of osteoporosis, nucleus pulposus degeneration, annulus fibrosus rupture, cartilaginous endplate degeneration of IVDD, and sarcopenia, ER stress is involved in the pathogenesis of degenerative musculoskeletal diseases. Preclinical studies have found that regulation of ER stress can delay the progression of multiple degenerative musculoskeletal diseases. These pilot studies provide foundations for further evaluation of the feasibility, efficacy, and safety of ER stress modulators in the treatment of musculoskeletal degenerative diseases in clinical trials. In this review, we have integrated up-to-date research findings of ER stress into the pathogenesis of degenerative musculoskeletal diseases. In a future perspective, we have also discussed possible directions of ER stress in the investigation of degenerative musculoskeletal disease, potential therapeutic strategies for degenerative musculoskeletal diseases using ER stress modulators, as well as underlying challenges and obstacles in bench-to-beside research.

A Metabolomics Study of Feces Revealed That a Disturbance of Selenium-Centered Metabolic Bioprocess Was Involved in Kashin-Beck Disease, an Osteoarthropathy Endemic to China

Background: Kashin-Beck disease (KBD) is a distinct osteoarthropathy in China with an unclear pathogenesis. This study aims to explore whether perturbations in the intestine metabolome could be linked to KBD individuals. Methods: An investigation was conducted in KBD endemic villages and fecal samples were collected. After applying inclusion and exclusion criteria, a total of 75 subjects were enrolled for this study, including 46 KBD (including 19 Grade I KBD and 27 Grade II KBD) and 29 controls. Untargeted metabolomics analysis was performed on the platform of UHPLC-MS. PLS-DA and OPLS-DA were conducted to compare the groups and identify the differential metabolites (DMs). Pathway analysis was conducted on MPaLA platform to explore the functional implication of the DMs. Results: Metabolomics analysis showed that compared with the control group, KBD individuals have a total of 584 differential metabolites with dysregulated levels such as adrenic acid (log2FC = -1.87, VIP = 4.84, p = 7.63 × 10-7), hydrogen phosphate (log2FC = -2.57, VIP = 1.27, p = 1.02 × 10-3), taurochenodeoxycholic acid (VIP = 1.16, log2FC = -3.24, p = 0.03), prostaglandin E3 (VIP = 1.17, log2FC = 2.67, p = 5.61 × 10-4), etc. Pathway analysis revealed several significantly perturbed pathways associated with KBD such as selenium micronutrient network (Q value = 3.11 × 10-3, Wikipathways), metabolism of lipids (Q value = 8.43 × 10-4, Reactome), free fatty acid receptors (Q value = 3.99 × 10-3, Reactome), and recycling of bile acids and salts (Q value = 2.98 × 10-3, Reactome). Subgroup comparisons found a total of 267 differential metabolites were shared by KBD vs. control, KBD II vs. control, and KBD I vs. control, while little difference was found between KBD II and KBD I (only one differential metabolite detected). Conclusions: KBD individuals showed distinct metabolic features characterized by perturbations in lipid metabolism and selenium-related bioprocesses. Our findings suggest that the loss of nutrients metabolism balance in intestine was involved in KBD pathogenesis. Linking the nutrients metabolism (especially selenium and lipid) to KBD cartilage damage should be a future direction of KBD study.

Bile acid metabolism regulatory network orchestrates bone homeostasis

Bile acids (BAs), synthesized in the liver and modified by the gut microbiota, have been widely appreciated not only as simple lipid emulsifiers, but also as complex metabolic regulators and momentous signaling molecules, which play prominent roles in the complex interaction among several metabolic systems. Recent studies have drawn us eyes on the diverse physiological functions of BAs, to enlarge the knowledge about the "gut-bone" axis due to the participation about the gut microbiota-derived BAs to modulate bone homeostasis at physiological and pathological stations. In this review, we have summarized the metabolic processes of BAs and highlighted the crucial roles of BAs targeting bile acid-activated receptors, promoting the proliferation and differentiation of osteoblasts (OBs), inhibiting the activity of osteoclasts (OCs), as well as reducing articular cartilage degradation, thus facilitating bone repair. In addition, we have also focused on the bidirectional effects of BA signaling networks in coordinating the dynamic balance of bone matrix and demonstrated the promising effects of BAs on the development or treatment for pathological bone diseases. In a word, further clinical applications targeting BA metabolism or modulating gut metabolome and related derivatives may be developed as effective therapeutic strategies for bone destruction diseases.

Chronic obstructive pulmonary disease and emerging ER stress-related therapeutic targets

COPD pathogenesis is frequently associated with endoplasmic reticulum stress (ER stress) progression. Targeting the major unfolded protein response (UPR) branches in the ER stress pathway may provide pharmacotherapeutic selection strategies for treating COPD and enable relief from its symptoms. In this study, we aimed to systematically review the potential role of the ER stress inhibitors of major UPR branches (IRE1, PERK, and ATF6) in COPD-related studies and determine the current stage of knowledge in this field. The systematic review was carried out adhering to the PRISMA checklist based on published studies obtained from specific keyword searches of three databases, namely PubMed, ScienceDirect and Springer Database. The search was limited to the year 2000-2022 which includes all in vitro studies, in vivo studies and clinical trials related to the application of ER stress inhibitors toward COPD-induced models and disease. The risk of bias was evaluated using the QUIN, SYRCLE, revised Cochrane risk of bias tool for randomized trials (RoB 2.0) and NIH tool respectively. A total of 7828 articles were screened from three databases and a final total of 37 studies were included in the review. The ER stress and UPR pathways are potentially useful to prevent COPD progression and attenuate the exacerbation of COPD and related symptoms. Interestingly, the off-target effects from inhibition of the UPR pathway may be desirable or undesirable depending on context and therapeutic applications. Targeting the UPR pathway could have complex consequences as the production of ER molecules involved in folding may be impaired which could continuously provoke misfolding of proteins. Although several emerging compounds were noted to be potentially useful for targeted therapy against COPD, clinical studies have yet to be thoroughly explored.

The novel role of ER protein TXNDC5 in the pathogenesis of organ fibrosis: mechanistic insights and therapeutic implications

Fibrosis-related disorders account for an enormous burden of disease-associated morbidity and mortality worldwide. Fibrosis is defined by excessive extracellular matrix deposition at fibrotic foci in the organ tissue following injury, resulting in abnormal architecture, impaired function and ultimately, organ failure. To date, there lacks effective pharmacological therapy to target fibrosis per se, highlighting the urgent need to identify novel drug targets against organ fibrosis. Recently, we have discovered the critical role of a fibroblasts-enriched endoplasmic reticulum protein disulfide isomerase (PDI), thioredoxin domain containing 5 (TXNDC5), in cardiac, pulmonary, renal and liver fibrosis, showing TXNDC5 is required for the activation of fibrogenic transforming growth factor-β signaling cascades depending on its catalytic activity as a PDI. Moreover, deletion of TXNDC5 in fibroblasts ameliorates organ fibrosis and preserves organ function by inhibiting myofibroblasts activation, proliferation and extracellular matrix production. In this review, we detailed the molecular and cellular mechanisms by which TXNDC5 promotes fibrogenesis in various tissue types and summarized potential therapeutic strategies targeting TXNDC5 to treat organ fibrosis.

Endoplasmic Reticulum Stress in Osteoarthritis: A Novel Perspective on the Pathogenesis and Treatment

Osteoarthritis (OA), the most common degenerative joint disease, causes an enormous socioeconomic burden due to its disabling properties and high prevalence. Increasing evidence suggests that OA is a whole-joint disease involving cartilage degradation, synovitis, meniscal lesions, and subchondral bone remodeling. Endoplasmic reticulum (ER) stress is the accumulation of misfolded/unfolded proteins in the ER. Recent studies have found that ER stress is involved in the OA pathological changes by influencing the physiological function and survival of chondrocytes, fibroblast-like synoviocytes, synovial macrophages, meniscus cells, osteoblasts, osteoclasts, osteocytes, and bone marrow mesenchymal stem cells. Therefore, ER stress is an attractive and promising target for OA. However, although targeting ER stress has been proven to alleviate OA progression in vitro and in vivo, the treatments for OA remain in preclinical stage and require further investigation.

Activation of the alpha 7 nicotinic acetylcholine receptor mitigates osteoarthritis progression by inhibiting NF-κB/NLRP3 inflammasome activation and enhancing autophagy

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by cartilage degradation. Alpha 7 nicotinic acetylcholine receptor (α7nAChR) is associated with inflammatory and metabolic responses in OA. However, the mechanisms underlying the pathological process of OA remain unclear. The aim of the present study was to examine the role and mechanisms of α7nAChR-mediated autophagy and anti-inflammatory response in chondroprotection. Monosodium iodoacetate (MIA)-induced Wistar rat OA model was used to assess the in vivo effects of the ɑ7nAChR agonist (PNU-282987). The histopathological characteristics of OA were evaluated by immunohistochemistry (IHC), and the levels of autophagy markers were determined by western blotting and transmission electron microscopy. The anti-inflammatory effect of the ɑ7nAChR agonist was assessed by IHC, quantitative real-time polymerase chain reaction, and western blotting. Parallel experiments to determine the molecular mechanisms through which the ɑ7nAChR agonist prevents OA were performed using interleukin-1β (IL-1β)-treated chondrocytes. Our results showed that PNU-282987 reduced cartilage degeneration and matrix metalloproteinase (MMP)-1 and MMP-13 expressions. Activating α7nAChR with PNU-282987 significantly promoted MIA/IL-1β-induced chondrocyte autophagy, as demonstrated by the increase in LC3-II/LC3-I ratio, Beclin-1 levels, and autophagosome number. Furthermore, treating chondrocyte with ULK1 siRNA attenuated the PNU282987-induced enhancement of LC3-II/LC3-I ratio and Beclin-1 level. Additionally, PNU282987 suppressed NF-κB/NLRP3 inflammasome activation by inhibiting the ROS/TXNIP pathway and suppressed tumor necrosis factor-ɑ and IL-1β secretion in MIA/IL-1β-treated chondrocytes. Our results demonstrate that the activation of α7nAChR promotes chondrocyte autophagy and attenuates inflammation to mitigate OA progression, providing a novel target for the treatment of OA.

Molecular and Cellular Effects of Chemical Chaperone-TUDCA on ER-Stressed NHAC-kn Human Articular Chondrocytes Cultured in Normoxic and Hypoxic Conditions

Osteoarthritis (OA) is considered one of the most common arthritic diseases characterized by progressive degradation and abnormal remodeling of articular cartilage. Potential therapeutics for OA aim at restoring proper chondrocyte functioning and inhibiting apoptosis. Previous studies have demonstrated that tauroursodeoxycholic acid (TUDCA) showed anti-inflammatory and anti-apoptotic activity in many models of various diseases, acting mainly via alleviation of endoplasmic reticulum (ER) stress. However, little is known about cytoprotective effects of TUDCA on chondrocyte cells. The present study was designed to evaluate potential effects of TUDCA on interleukin-1β (IL-1β) and tunicamycin (TNC)-stimulated NHAC-kn chondrocytes cultured in normoxic and hypoxic conditions. Our results showed that TUDCA alleviated ER stress in TNC-treated chondrocytes, as demonstrated by reduced CHOP expression; however, it was not effective enough to prevent apoptosis of NHAC-kn cells in either normoxia nor hypoxia. However, co-treatment with TUDCA alleviated inflammatory response induced by IL-1β, as shown by down regulation of Il-1β, Il-6, Il-8 and Cox2, and increased the expression of antioxidant enzyme Sod2. Additionally, TUDCA enhanced Col IIα expression in IL-1β- and TNC-stimulated cells, but only in normoxic conditions. Altogether, these results suggest that although TUDCA may display chondoprotective potential in ER-stressed cells, further analyses are still necessary to fully confirm its possible recommendation as potential candidate in OA therapy.

Review: ER stress-induced cell death in osteoarthritic cartilage

In cartilage, chondrocytes are responsible for the biogenesis and maintenance of the extracellular matrix (ECM) composed of proteins, glycoproteins and proteoglycans. Various cellular stresses, such as hypoxia, nutrient deprivation, oxidative stress or the accumulation of advanced glycation end products (AGEs) during aging, but also translational errors or mutations in cartilage components or chaperone proteins affect the synthesis and secretion of ECM proteins, causing protein aggregates to accumulate in the endoplasmic reticulum (ER). This condition, referred to as ER stress, interferes with cartilage cell homeostasis and initiates the unfolded protein response (UPR), a rescue mechanism to regain cell viability and function. Chronic or irreversible ER stress, however, triggers UPR-initiated cell death. Due to unresolved ER stress in chondrocytes, diseases of the skeletal system, such as chondrodysplasias, arise. ER stress has also been identified as a contributing factor to the pathogenesis of cartilage degeneration processes such as osteoarthritis (OA). This review provides current knowledge about the biogenesis of ECM components in chondrocytes, describes possible causes for the impairment of involved processes and focuses on the ER stress-induced cell death in articular cartilage during OA. Targeting of the ER stress itself or intervention in UPR signaling to reduce death of chondrocytes may be promising for future osteoarthritis therapy.

Mitochondria: Potential Targets for Osteoarthritis

Osteoarthritis (OA) is a common and disabling joint disorder that is mainly characterized by cartilage degeneration and narrow joint spaces. The role of mitochondrial dysfunction in promoting the development of OA has gained much attention. Targeting endogenous molecules to improve mitochondrial function is a potential treatment for OA. Moreover, research on exogenous drugs to improve mitochondrial function in OA based on endogenous molecular targets has been accomplished. In addition, stem cells and exosomes have been deeply researched in the context of cartilage regeneration, and these factors both reverse mitochondrial dysfunctions. Thus, we hypothesize that biomedical approaches will be applied to the treatment of OA. Furthermore, we have summarized the global status of mitochondria and osteoarthritis research in the past two decades, which will contribute to the research field and the development of novel treatment strategies for OA.

The endoplasmic reticulum stress induced by tunicamycin affects the viability and autophagy activity of chondrocytes

Osteoarthritis (OA) is attributed to a reduction in chondrocytes within joint cartilage, and research has shown that endoplasmic reticulum (ER) stress and autophagy play important roles in the survival of chondrocytes. However, the relationship between ER stress and autophagy in chondrocytes remains unclear. In this study, we investigated the changes in apoptotic and autophagic activity in chondrocytes under ER stress. Following treatment with tunicamycin, the rate of apoptosis among chondrocytes increased. Western blot analysis showed the levels of unfolded protein response (UPR) related proteins increased, followed by elevated expression of light chain 3B‐II (LC3B‐II) and Beclin‐1. An ultrastructural investigation showed that a large number of pre‑autophagosomal structures or autophagosomes formed under tunicamycin treatment. However, the autophagy activity was significantly inhibited in chondrocytes after suppression of GRP78 by siRNA. The apoptosis ratio of chondrocytes pre‐treated with 3‐methyladenine was much higher than that of normal chondrocytes after exposure to tunicamycin. Our study revealed that the tunicamycin‐induced persistent UPR expression led to apoptosis of chondrocytes and activation of autophagy incorporation with GRP78. Blocking autophagy accelerated the apoptosis induced by ER stress, which confirmed the protective function of autophagy in the homeostasis of chondrocytes. These findings advance our understanding of chondrocyte apoptosis and provide potential molecular targets for preventing apoptotic death of chondrocytes.

Tauroursodeoxycholate-Bile Acid with Chaperoning Activity: Molecular and Cellular Effects and Therapeutic Perspectives

Tauroursodeoxycholic acid (TUDCA) is a naturally occurring hydrophilic bile acid that has been used for centuries in Chinese medicine. Chemically, TUDCA is a taurine conjugate of ursodeoxycholic acid (UDCA), which in contemporary pharmacology is approved by Food and Drug Administration (FDA) for treatment of primary biliary cholangitis. Interestingly, numerous recent studies demonstrate that mechanisms of TUDCA functioning extend beyond hepatobiliary disorders. Thus, TUDCA has been demonstrated to display potential therapeutic benefits in various models of many diseases such as diabetes, obesity, and neurodegenerative diseases, mostly due to its cytoprotective effect. The mechanisms underlying this cytoprotective activity have been mainly attributed to alleviation of endoplasmic reticulum (ER) stress and stabilization of the unfolded protein response (UPR), which contributed to naming TUDCA as a chemical chaperone. Apart from that, TUDCA has also been found to reduce oxidative stress, suppress apoptosis, and decrease inflammation in many in-vitro and in-vivo models of various diseases. The latest research suggests that TUDCA can also play a role as an epigenetic modulator and act as therapeutic agent in certain types of cancer. Nevertheless, despite the massive amount of evidence demonstrating positive effects of TUDCA in pre-clinical studies, there are certain limitations restraining its wide use in patients. Here, molecular and cellular modes of action of TUDCA are described and therapeutic opportunities and limitations of this bile acid are discussed.

4-Phenylbutyric Acid Reduces Endoplasmic Reticulum Stress in Chondrocytes That Is Caused by Loss of the Protein Disulfide Isomerase ERp57

Objective

The integrity of cartilage depends on the correct synthesis of extracellular matrix (ECM) components. In case of insufficient folding of proteins in the endoplasmic reticulum (ER) of chondrocytes, ECM proteins aggregate, ER stress evolves, and the unfolded protein response (UPR) is initiated. By this mechanism, chondrocytes relieve the stress condition or initiate cell death by apoptosis. Especially persistent ER stress has emerged as a pathogenic mechanism in cartilage diseases, such as chondrodysplasias and osteoarthritis. As pharmacological intervention is not available yet, it is of great interest to understand cartilage ER stress in detail and to develop therapeutics to intervene.

Methods

ERp57-deficient chondrocytes were generated by CRISPR/Cas9-induced KO. ER stress and autophagy were studied on mRNA and protein level as well as by transmission electron microscopy (TEM) in chondrocyte micromass or cartilage explant cultures of ERp57 KO mice. Thapsigargin (Tg), an inhibitor of the ER-residing Ca²⁺-ATPase, and 4-Phenylbutyric acid (4-PBA), a small molecular chemical chaperone, were applied to induce or inhibit ER stress.

Results

Our data reveal that the loss of the protein disulfide isomerase ERp57 is sufficient to induce ER stress in chondrocytes. 4-PBA efficiently diffuses into cartilage explant cultures and diminishes excessive ER stress in chondrocytes dose dependently, no matter if it is induced by ERp57 KO or stimulation with Tg.

Conclusion

ER-stress-related diseases have different sources; therefore, various targets for therapeutic treatment exist. In the future, 4-PBA may be used alone or in combination with other drugs for the treatment of ER-stress-related skeletal disorders in patients.

Taurine alleviates endoplasmic reticulum stress in the chondrocytes from patients with osteoarthritis

Osteoarthritis (OA), characterized by pain and stiffness, swelling, deformity and dysfunction of joints, affects large numbers of population. The purpose of this study was to discover the effects of taurine in human OA chondrocytes and explore the underlying mechanisms. 46 patients with different grades of OA were recruited. Of these patients, 24 underwent total knee replacement and cartilages were harvested. The mRNA expressions of type II collagen (Collagen II) and endoplasmic reticulum (ER) stress markers (GRP78, GADD153 and Caspase-12) in cartilages were quantified by qRT-PCR. Cell viability and apoptosis of patient-derived chondrocytes were assessed by the CCK-8 assay and flow cytometry assay, respectively. Meanwhile, protein levels of Collagen II and ER stress markers both in cartilages and chondrocytes were evaluated by Western blot. The mRNA and protein levels of Collagen II decreased as OA progressed, while the expressions of ER stress markers increased dramatically. H₂O₂ induced ER stress in chondrocytes, as shown by the significant increase in the expression of ER stress markers, inhibited chondrocyte viability and Collagen II synthesis, promoted apoptosis. However, taurine treatment inhibited these above phenomena. These results indicated that taurine exhibited anti-OA effect by alleviating H₂O₂ induced ER stress and subsequently inhibiting chondrocyte apoptosis.

Taurine protects against knee osteoarthritis development in experimental rat models

BACKGROUND

Osteoarthritis (OA) is one of the complex diseases that affect a large population of the world. The aim of the current study was to explore the roles of taurine in OA rat models, and discover the related mechanisms.

METHODS

OA rat models were established by anterior cruciate ligament transection (ACLT) plus medial meniscus resection (MMx) surgery on the right knees. Secondary mechanical allodynia, weight-bearing alterations and knee joint width were evaluated before surgery and every two weeks after surgery. At 14weeks, histopathological analysis was conducted on the knee joint cartilage. Protein amount of MMP-3 and CHOP was evaluated by western blot.

RESULTS

Taurine injection after surgery significantly relieved the symptoms of OA in rat models in a dose-dependent and time-dependent manner, as shown by alleviation of secondary mechanical allodynia, decrease in hind limb weight-bearing alterations, and inhibited knee swelling. Moreover, histopathological analysis showed that taurine inhibited matrix loss and cartilage degeneration in a dose-dependent manner. Taurine administration strikingly suppressed the expression of matrix metalloproteinase-3 (MMP-3) and CHOP.

CONCLUSION

These results indicated that taurine administration exhibited protective effects by inhibiting MMP-3 and CHOP expression, and subsequently alleviated the OA symptoms in experimental rat models.

Tauroursodeoxycholic Acid Protects Nucleus Pulposus Cells from Compression-Induced Apoptosis and Necroptosis via Inhibiting Endoplasmic Reticulum Stress

Tauroursodeoxycholic acid (TUDCA) is a kind of hydrophilic bile acid, which could protect cells from death via inhibiting endoplasmic reticulum (ER) stress. However, the role of TUDCA in compression-induced intervertebral disc degeneration (IVDD) has not been elucidated. Here, we used a previously described device to mimic in vivo compression conditions. NP cells treated with DMSO or TUDCA were exposed to compression. Then, cell viability, morphology, and apoptosis were detected. Furthermore, apoptosis-related proteins and necroptosis markers were detected too. To investigate the specific cytoprotective mechanisms of TUDCA in IVDD, we detected the ER morphology by electron microscopy. In addition, the ER stress of nucleus pulposus (NP) cells was quantitatively evaluated by analyzing the level of ER-stress-associated proteins. Our results revealed that TUDCA could protect NP cells from excessive compression-induced death by reducing the apoptosis and necroptosis. In addition, ER stress is involved in pathogenesis of IVDD induced by excessive compression and plays a detrimental role. TUDCA exerts its protective functions by inhibiting ER stress. In conclusion, TUDCA could protect NP cells from compression-induced death, which suggested that treatment by TUDCA may be a potential method to retard IVDD.

Tauroursodeoxycholic Acid Protects against the Effects of P-Cresol-Induced Reactive Oxygen Species via the Expression of Cellular Prion Protein

Mesenchymal stem cells (MSCs) could be a promising solution in the treatment of various diseases including chronic kidney disease (CKD). However, endoplasmic reticulum (ER) stress induced by ischemia in the area of application limits the integration and survival of MSCs in patients. In our study, we generated ER stress-induced conditions in MSCs using P-cresol. As P-cresol is a toxic compound accumulated in the body of CKD patients and induces apoptosis and inflammation through reactive oxygen species (ROS), we observed ER stress-induced MSC apoptosis activated by oxidative stress, which in turn resulted from ROS generation. To overcome stress-induced apoptosis, we investigated the protective effects of tauroursodeoxycholic acid (TUDCA), a bile acid, on ER stress in MSCs. In ER stress, TUDCA treatment of MSCs reduced ER stress-associated protein activation, including GRP78, PERK, eIF2α, ATF4, IRE1α, and CHOP. Next, to explore the protective mechanism adopted by TUDCA, TUDCA-mediated cellular prion protein (PrP^C) activation was assessed. We confirmed that PrP^C expression significantly increased ROS, which was eliminated by superoxide dismutase and catalase in MSCs. These findings suggest that TUDCA protects from inflammation and apoptosis in ER stress via PrP^C expression. Our study demonstrates that TUDCA protects MSCs against inflammation and apoptosis in ER stress by PrP^C expression in response to P-cresol exposure.

Icariin Regulates Cellular Functions and Gene Expression of Osteoarthritis Patient-Derived Human Fibroblast-Like Synoviocytes

Synovial inflammation plays an important role in the pathogenesis and progress of osteoarthritis (OA). There is an urgent need to find safe and effective drugs that can reduce the inflammation and regulate the pathogenesis of cytokines of the OA disease. Here, we investigated the effect of icariin, the major pharmacological active component of herb Epimedium on human osteoarthritis fibroblast-like synoviocytes (OA–FLSs). The OA–FLSs were isolated from patients with osteoarthritis and cultured in vitro with different concentrations of icariin. Then, cell viability, proliferation, and migration were investigated; MMP14, GRP78, and IL-1β gene expression levels were detected via qRT-PCR. Icariin showed low cytotoxicity to OA–FLSs at a concentration of under 10 μM and decreased the proliferation of the cells at concentrations of 1 and 10 μM. Icariin inhibited cell migration with concentrations ranging from 0.1 to 1 μM. Also, the expression of three cytokines for the pathogenesis of OA which include IL-1β, MMP14 and GRP78 was decreased by the various concentrations of icariin. These preliminary results imply that icariin might be an effective compound for the treatment of OA disease.

Could Oxidative Stress Regulate the Expression of MicroRNA-146a and MicroRNA-34a in Human Osteoarthritic Chondrocyte Cultures?

Oxidative stress and the overproduction of reactive oxygen species (ROS) play an important role in the pathogenesis of osteoarthritis (OA). Accumulating evidence has demonstrated the involvement of microRNAs (miRNAs) dysregulation in disease development and progression. In this study, we evaluated the effect of oxidative stress on miR-146a and miR-34a expression levels in human OA chondrocytes cultures stimulated by H₂O₂. Mitochondrial ROS production and cell apoptosis were detected by flow cytometry. The antioxidant enzymes SOD-2, CAT, GPx, the transcriptional factor NRF2 and the selected miRNAs were analyzed by qRT-PCR. The H₂O₂-induced oxidative stress was confirmed by a significant increase in superoxide anion production and of the apoptotic ratio. Furthermore, H₂O₂ significantly up-regulated the expression levels of SOD-2, CAT, GPx and NRF2, and modulated miR-146a and miR-34a gene expression. The same analyses were carried out after pre-treatment with taurine, a known antioxidant substance, which, in our experience, counteracted the H₂O₂-induced effect. In conclusion, the induction of oxidative stress affected cell apoptosis and the expression of the enzymes involved in the oxidant/antioxidant balance. Moreover, we demonstrated for the first time the modification of miR-146a and miR-34a in OA chondrocytes subjected to H₂O₂ stimulus and we confirmed the antioxidant effect of taurine.

Effect of Scutellarin inhibits collagen‑induced arthritis through TLR4/NF‑κB‑mediated inflammation

Scutellarin is the major effective constituent of the commonly used Chinese medicine Erigeron breviscapus. It has been applied in the clinic to treat various diseases, and is characterized by high content, a stable source, controllable quality, high efficiency and low toxicity. In addition, its potential pharmacological effects have been increasingly identified and elucidated. The present study was performed to examine the role of scutellarin on collagen‑induced arthritis (CIA). Mice were injected subcutaneously with bovine collagen type II and administered scutellarin for 2 weeks by gavage 20 mg/kg/day. ELISA kits were used to measure the levels of interleukin (IL)‑1β, IL‑6, tumor necrosis factor‑α (TNF‑α), oxidative stress markers [superoxide dismutase (SOD) and malondialdehyde (MDA)] and caspase‑3/-9 activity. Bax, Bcl‑2, toll like receptor 4 (TLR4) and nuclear factor (NF)‑κB protein expression was analyzed using western immunoblot analyses. The present study demonstrated that scutellarin prevented CIA, and inhibited the expression of inflammation factors, IL‑1β, IL‑6 and TNF‑α. In addition, scutellarin reduced the levels of oxidative stress markers, SOD and MDA, as well as intercellular adhesion molecule‑1 and monocyte chemoattractant protein 1 in CIA mice. Caspase‑3/-9, Bax/Bcl‑2, TLR4 and NF‑κB protein expression were reduced in CIA mice following scutellarin treatment. The results of the current study suggest a novel effect of scutellarin involving the inhibition of TLR4/NF‑κB‑mediated inflammation.

Piezo1 protein induces the apoptosis of human osteoarthritis-derived chondrocytes by activating caspase-12, the signaling marker of ER stress

The present study was carried out to determine whether the mechanically activated cation channel Piezo1 protein plays a role as a signaling pathway which causes the apoptosis of human chondrocytes. The chondrocytes were isolated, cultured, and then subjected to mechanical stretch force for 0, 2, 12, 24 and 48 h, respectively. The expression levels of Piezo1 and the apoptosis-related protein caspase-12 were assessed by reverse transcription-quantitative polymerase chain reaction, as well as the apoptosis-related genes, B cell lymphoma/leukemia-2 (Bcl-2), Bcl-associated X protein (Bax) and Bcl-2-associated death promoter (BAD). Lactate dehydrogenase (LDH) activity was used to discern dead cells. Piezo1 expression was determined by immunofluorescence. In addition, Piezo1 inhibitor, GsMTx4, was used to block the mechanically activated (MA) cation channel Piezo1, and served as a positive control. The results showed that the osteoarthritis (OA)-derived chondrocytes showed a tendency to undergo late-stage apoptosis under compressive loading. Piezo1 and caspase-12 were significantly upregulated under static compressive stimuli and the expression was related to the rate of apoptosis of the OA-derived chondrocytes during compressive loading. The expression of caspase-12 and late-stage apoptosis of the human OA-derived chondrocytes were repressed by GsMTx4, the specific inhibitor of Piezo1, while the expression of Piezo1 and the induction of the apoptosis of the OA-derived chondrocytes during compressive loading was not totally blocked. Thus, we conclude that Piezo1 plays an important role in the apoptosis of human OA-derived chondrocytes through a caspase-12-dependent pathway. The expression of Piezo1 protein was not totally inhibited by GsMTx4.

Metabolic syndrome enhances endoplasmic reticulum, oxidative stress and leukocyte-endothelium interactions in PCOS

OBJECTIVE

Polycystic ovary syndrome (PCOS) is associated with insulin resistance, which can lead to metabolic syndrome (MetS). Oxidative stress and leukocyte-endothelium interactions are related to PCOS. Our aim was to evaluate whether the presence of MetS in PCOS patients can influence endoplasmic reticulum (ER) and oxidative stress and leukocyte-endothelium interactions.

MATERIAL AND METHODS

This was a prospective controlled study conducted in an academic medical center. The study population consisted of 148 PCOS women (116 without/32 with MetS) and 112 control subjects (87 without / 25 with MetS). Metabolic parameters, reactive oxygen species (ROS) production, ER stress markers (GRP78, sXBP1, ATF6), leukocyte-endothelium interactions, adhesion molecules (VCAM-1, ICAM-1, E-Selectin), TNF-α and IL-6 were determined.

RESULTS

Total ROS, inflammatory parameters and adhesion molecules were enhanced in the presence of MetS (p<0.05), and the PCOS+MetS group showed higher levels of IL-6 and ICAM-1 than controls (p<0.05). Increased adhesion and leukocyte rolling flux were observed in PCOS and PCOS+MetS groups vs their respective controls (p<0.05). GRP78 protein expression was higher in the PCOS groups (p<0.05 vs controls) and sXBP1 was associated with the presence of MetS (p<0.05 vs controls without MetS). Furthermore, PCOS+MetS patients exhibited higher GRP78 and ATF6 levels than controls and PCOS patients without MetS (p<0.05). In PCOS women, HOMA-IR was positively correlated with ICAM-1 (r=0.501; p<0.01), ROS (r=0.604; p<0.01), rolling flux (r=0.455;p<0.05) and GRP78 (r=0.574; p<0.001).

CONCLUSION

Our findings support the hypothesis of an association between altered metabolic status, increased ROS production, ER stress and leukocyte-endothelium interactions in PCOS, all of which are related to vascular complications.

Tauroursodeoxycholic acid reduces ER stress by regulating of Akt-dependent cellular prion protein

Although mesenchymal stem cells (MSCs) are a promising cell source for regenerative medicine, ischemia-induced endoplasmic reticulum (ER) stress induces low MSC engraftment and limits their therapeutic efficacy. To overcome this, we investigated the protective effect of tauroursodeoxycholic acid (TUDCA), a bile acid, on ER stress in MSCs in vitro and in vivo. In ER stress conditions, TUDCA treatment of MSCs reduced the activation of ER stress-associated proteins, including GRP78, PERK, eIF2α, ATF4, IRE1α, JNK, p38, and CHOP. In particular, TUDCA inhibited the dissociation between GRP78 and PERK, resulting in reduced ER stress-mediated cell death. Next, to explore the ER stress protective mechanism induced by TUDCA treatment, TUDCA-mediated cellular prion protein (PrP^C) activation was assessed. TUDCA treatment increased PrP^C expression, which was regulated by Akt phosphorylation. Manganese-dependent superoxide dismutase (MnSOD) expression also increased significantly in response to signaling through the TUDCA-Akt axis. In a murine hindlimb ischemia model, TUDCA-treated MSC transplantation augmented the blood perfusion ratio, vessel formation, and transplanted cell survival more than untreated MSC transplantation did. Augmented functional recovery following MSC transplantation was blocked by PrP^C downregulation. This study is the first to demonstrate that TUDCA protects MSCs against ER stress via Akt-dependent PrP^C and Akt-MnSOD pathway.

Causes and consequences of endoplasmic reticulum stress in rheumatic disease

Rheumatic diseases represent a heterogeneous group of inflammatory conditions, many of which involve chronic activation of both innate and adaptive immune responses by multiple genetic and environmental factors. These immune responses involve the secretion of excessive amounts of cytokines and other signalling mediators by activated immune cells. The endoplasmic reticulum (ER) is the cellular organelle that directs the folding, processing and trafficking of membrane-bound and secreted proteins, including many key components of the immune response. Maintaining homeostasis in the ER is critical to cell function and survival. Consequently, elaborate mechanisms have evolved to sense and respond to ER stress through three main signalling pathways that together comprise the unfolded protein response (UPR). Activation of the UPR can rapidly resolve the accumulation of misfolded proteins, direct permanent changes in the size and function of cells during differentiation, and critically influence the immune response and inflammation. Recognition of the importance of ER stress and UPR signalling pathways in normal and dysregulated immune responses has greatly increased in the past few years. This Review discusses several settings in which ER stress contributes to the pathogenesis of rheumatic diseases and considers some of the therapeutic opportunities that these discoveries provide.