Up-regulation of the chemo-attractive receptor ChemR23 and occurrence of apoptosis in human chondrocytes isolated from fractured calcaneal osteochondral fragments

Lipoxin A4 modulates the PKA/CREB and NF-κB signaling pathway to mitigate chondrocyte catabolism and apoptosis in temporomandibular joint osteoarthritis

Temporomandibular joint osteoarthritis (TMJ-OA) is characterized by the degradation of the extracellular matrix (ECM) in cartilage and the apoptosis of chondrocytes, which is caused by inflammation and disruptions of chondrocyte metabolism and inflammation. Lipoxin A4 (LXA4), a specialized pro-resolving mediator, has been shown to inhibit inflammation and regulate the balance between ECM synthesis and degradation. However, the therapeutic effects of LXA4 on TMJ-OA and its underlying mechanisms remain unclear. Interleukin-1 beta (IL-1β)-induced chondrocyte and surgically induced TMJ-OA rat models were established in this study. The viability of chondrocytes treated with LXA4 was evaluated with the cell counting kit-8 (CCK-8) assay, while protein levels were assessed by western blot analysis, and the apoptosis rate was evaluated with terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labelling (TUNEL) staining. Histological analysis was conducted to evaluate the impact of LXA4 on cartilage degradation in TMJ-OA rat models. In vitro, the qRT-PCR and western blot analysis demonstrated that LXA4 facilitated the upregulation of collagen proteins (Collagen II) and decreased expression of matrix metalloproteinases (MMP-3, and MMP-13) associated with ECM modulation. LXA4 enhanced the TMJ-OA chondrocyte viability and decreased apoptotic rate. In vivo, histology and immunohistochemistry (IHC) analysis revealed that intraperitoneal injection of LXA4 contributed to the amelioration of chondrocyte injuries and deceleration of TMJ-OA. Transcriptomic sequencing revealed that cAMP signaling pathway was up-regulated and NF-κB signaling pathway was down-regulated in LXA4 treated group. LXA4 inhibited the phosphorylation of P65 and inhibitor of nuclear factor kappa B (IκBα) proteins while enhancing the phosphorylation PKA and CREB. This study demonstrates the potential of LXA4 as a therapeutic agent for suppressing chondrocyte catabolism and apoptosis by increasing PKA/CREB activity and decreasing NF-κB signaling.

Platelet-rich plasma attenuates interleukin-1β-induced apoptosis and inflammation in chondrocytes through targeting hypoxia-inducible factor-2α

Osteoarthritis (OA) is a prevailing chronic disease in Orthopedics that characterized with severely damaged cartilage and subchondral bone, thus leading to profound disorders of synovial joints. Platelet-rich plasma (PRP) has been applied as a popular non-operative treatment option for promoting musculoskeletal healing. Our previous work demonstrated that PRP protected chondrocytes from interleukin-1β (IL-1β)-induced apoptosis in vitro. However, the underlying mechanism behind the treatment remains unclear. The current study aimed to unveil the molecular signaling underlying its protective role in chondrocytes. Rat chondrocytes were isolated from newborn Sprague Dawley rats and treated with 5 ng/mL IL-1β for 24 h. The expression of hypoxia-inducible factor 2α (HIF-2α) was determined in both mRNA and protein levels. Next, loss- and gain-of-function assays for HIF-2α were performed using small-interfering RNA (siRNA) specific for HIF-2α and adenovirus-mediated HIF-2α overexpression, respectively. In addition, cell apoptosis markers, matrix metalloproteinase (MMP)-1, 3, -9 and -13, and extracellular matrix-related genes were evaluated. Our results demonstrated that IL-1β induced distinct inflammation in chondrocytes. In addition, HIF-2α upregulated in the IL-1β-treated chondrocytes compared to the untreated cells. Interestingly, 10% PRP protected chondrocytes against IL-1β-induced apoptosis and matrix degradation, and meanwhile suppressed the HIF-2α activation. Furthermore, HIF-2α siRNA and HIF-2α overexpression experiments indicated that PRP induced chondroprotection through targeting HIF-2α. Taken together, our findings indicated that PRP attenuates IL-1β-induced chondrocyte apoptosis and inflammation at least partially through inhibiting HIF-2α.

Leonurine Exerts Anti-Catabolic and Anti-Apoptotic Effects via Nuclear Factor kappa B (NF-κB) and Mitogen-Activated Protein Kinase (MAPK) Signaling Pathways in Chondrocytes

Background

Leonurine confers neuroprotection, inhibits myocardial apoptosis, ameliorates endothelial dysfunction, and shows anti-inflammatory effects, and may be beneficial for clinical applications. However, the effects of leonurine on chondrocytes remain unknown. Here, we investigated the protective role of leonurine in rat chondrocytes.

Material/Methods

To explore the potential therapeutic effect of leonurine against osteoarthritis (OA), rat chondrocytes were treated with IL-1β along with different concentrations of leonurine in vitro. The levels of matrix metalloproteinases (MMPs), ADAMTS, Bax, and Bcl-2 were measured by PCR, ELISA, and Western blotting. Caspase-3 activity in chondrocytes was determined using a caspase-3 activity assay. Western blotting was also performed to examine activation of the NF-κB and mitogen-activated protein kinase (MAPK) pathways to elucidate the likely regulatory mechanisms.

Results

Leonurine counteracted IL-1β-induced production of MMP-1, MMP-13, ADAMTS-4, and ADAMTS-5. Leonurine treatment reduced both the mRNA and protein levels of Bax and increased the level of Bcl-2. Leonurine also inhibited the activity of caspase-3 in IL-1β-induced chondrocytes. Furthermore, the activation of MAPK and phosphorylation of p65 were suppressed by leonurine.

Conclusions

The results of this study indicate that leonurine exerts anti-catabolic and anti-apoptotic effects in chondrocytes in vitro via suppression of the NF-κB and MAPK signaling pathways.

Platelet-rich plasma protects rat chondrocytes from interleukin-1β-induced apoptosis

Interleukin (IL)-1β-induced chondrocyte apoptosis is associated with the pathogenesis of arthritis. Platelet‑rich plasma (PRP), which is derived from the patient's own blood and contains numerous growth factors, has the potential for arthritis treatment. Therefore, the present study aimed to determine the effects of PRP on chondrocyte apoptosis, under IL‑1β‑induced pathological conditions. Chondrocytes isolated from the knee joint of Sprague Dawley rats were used in the present study. Cell viability was determined using the Cell Counting kit‑8 assay, cell apoptosis was evaluated by flow cytometry, and the expression of apoptosis‑, anabolism‑ and catabolism-associated genes were detected by quantitative polymerase chain reaction; protein expression was detected by western blot analysis. The results demonstrated that 10% PRP in the culture medium increased chondrocyte proliferation, whereas IL‑1β induced cell apoptosis. Treatment with PRP significantly attenuated cell apoptosis in IL‑1β‑treated chondrocytes, and altered apoptosis‑associated expression at the gene and protein level. Furthermore, treatment with PRP significantly reduced matrix metalloproteinase production and promoted anabolism of cartilage extracellular matrix under IL‑1β treatment. The present study demonstrated the protective effects of PRP on chondrocyte apoptosis and extracellular matrix anabolism, and provided scientific evidence to support the potential use of PRP as a promising therapeutic strategy for the treatment of arthritis.

The Proteasome Inhibitor Bortezomib Maintains Osteocyte Viability in Multiple Myeloma Patients by Reducing Both Apoptosis and Autophagy: A New Function for Proteasome Inhibitors

Multiple myeloma (MM) is characterized by severely imbalanced bone remodeling. In this study, we investigated the potential effect of proteasome inhibitors (PIs), a class of drugs known to stimulate bone formation, on the mechanisms involved in osteocyte death induced by MM cells. First, we performed a histological analysis of osteocyte viability on bone biopsies on a cohort of 37 MM patients with symptomatic disease. A significantly higher number of viable osteocytes was detected in patients treated with a bortezomib (BOR)-based regimen compared with those treated without BOR. Interestingly, both osteocyte autophagy and apoptosis were affected in vivo by BOR treatment. Thereafter, we checked the in vitro effect of BOR to understand the mechanisms whereby BOR maintains osteocyte viability in bone from MM patients. We found that osteocyte and preosteocyte autophagic death was triggered during coculturing with MM cells. Our evaluation was conducted by analyzing either autophagy markers microtubule-associated protein light chain 3 beta (LC3B) and SQSTM1/sequestome 1 (p62) levels, or the cell ultrastructure by transmission electron microscopy. PIs were found to increase the basal levels of LC3 expression in the osteocytes while blunting the myeloma-induced osteocyte death. PIs also reduced the autophagic death of osteocytes induced by high-dose dexamethasone (DEX) and potentiated the anabolic effect of PTH(1-34). Our data identify osteocyte autophagy as a new potential target in MM bone disease and support the use of PIs to maintain osteocyte viability and improve bone integrity in MM patients.

Chondrocyte Apoptosis in the Pathogenesis of Osteoarthritis

Apoptosis is a highly-regulated, active process of cell death involved in development, homeostasis and aging. Dysregulation of apoptosis leads to pathological states, such as cancer, developmental anomalies and degenerative diseases. Osteoarthritis (OA), the most common chronic joint disease in the elderly population, is characterized by progressive destruction of articular cartilage, resulting in significant disability. Because articular cartilage depends solely on its resident cells, the chondrocytes, for the maintenance of extracellular matrix, the compromising of chondrocyte function and survival would lead to the failure of the articular cartilage. The role of subchondral bone in the maintenance of proper cartilage matrix has been suggested as well, and it has been proposed that both articular cartilage and subchondral bone interact with each other in the maintenance of articular integrity and physiology. Some investigators include both articular cartilage and subchondral bone as targets for repairing joint degeneration. In late-stage OA, the cartilage becomes hypocellular, often accompanied by lacunar emptying, which has been considered as evidence that chondrocyte death is a central feature in OA progression. Apoptosis clearly occurs in osteoarthritic cartilage; however, the relative contribution of chondrocyte apoptosis in the pathogenesis of OA is difficult to evaluate, and contradictory reports exist on the rate of apoptotic chondrocytes in osteoarthritic cartilage. It is not clear whether chondrocyte apoptosis is the inducer of cartilage degeneration or a byproduct of cartilage destruction. Chondrocyte death and matrix loss may form a vicious cycle, with the progression of one aggravating the other, and the literature reveals that there is a definite correlation between the degree of cartilage damage and chondrocyte apoptosis. Because current treatments for OA act only on symptoms and do not prevent or cure OA, chondrocyte apoptosis would be a valid target to modulate cartilage degeneration.

Nitric oxide-associated chondrocyte apoptosis in trauma patients after high-energy lower extremity intra-articular fractures

BACKGROUND

The primary goal of this study was to identify nitric oxide (NO)-induced apoptosis in traumatized chondrocytes in intra-articular lower extremity fractures and the secondary goal was to identify the timeline of NO-induced apoptosis after injury.

MATERIALS AND METHODS

This is a prospective collection of samples of human cartilage harvested at the time of surgery to measure apoptotic cell death and the presence of NO by immunohistochemistry. Three patients met the criteria for control subjects and eight patients sustained high-energy intra-articular fractures and were included in the study. Subjects who sustained intra-articular acetabular, tibial, calcaneal and talus fracture had articular cartilage harvested at the time of surgical intervention. All 8 patients underwent open reduction and internal fixation of the displaced intra-articular fractures. The main outcome measures were rate of apoptosis, degree of NO-induced apoptosis in chondrocytes, and the timeline of NO-induced apoptosis after high-energy trauma.

RESULTS

The percentage of apoptotic chondrocytes was higher in impacted samples than in normal cartilage (56 vs 4 %), confirming the presence of apoptosis after intra-articular fracture. The percentage of cells with NO was greater in apoptotic cells than in normal cells (59 vs 20 %), implicating NO-induction of apoptosis. The correlation between chondrocyte apoptosis and increasing time from injury was found to be -0.615, indicating a decreasing rate of apoptosis post injury.

CONCLUSIONS

The data showed the involvement of NO-induced apoptosis of chondrocytes after high-energy trauma, which decreased with time from injury.

Chemerin/chemR23 axis in inflammation onset and resolution

Chemerin is an adipokine secreted by adipocytes and associated with obesity, insulin resistance and metabolic syndrome. Different chemerin fragments with pro- or anti-inflammatory action can be produced, depending on the class of proteases predominating in the microenvironment. Chemerin binds to three receptors, especially to chemR23, expressed on various cells, as dendritic cells, macrophages and natural killer cells, regulating chemotaxis towards the site of inflammation and activation status. Recently, the chemerin/chemR23 axis has attracted particular attention for the multiple roles related to the control of inflammation, metabolism and cancerogenesis in different organs and systems as lung (allergy and cancer), skin (psoriasis, lupus, cancer, wound repair), cardiovascular system (lipid profile and atherosclerosis), reproductive apparatus (polycystic ovary syndrome, follicular homoeostasis), and digestive tract (inflammatory bowel diseases and cancer). This pathway may regulate immune responses by contributing both to the pathogenesis of inflammatory diseases and to the resolution of acute inflammation. Thus, chemerin-derived peptides or other substances that may affect the chemerin/chemR23 axis could be used in the future for the treatment of many diseases, including cancer at different sites.