Restriction of spontaneous and prednisolone-induced leptin production to dedifferentiated state in human hip OA chondrocytes: role of Smad1 and β-catenin activation

Articular Cartilage Regeneration via Induced Chondrocyte Autophagy by Sustained Release of Leptin Inhibitor from Thermo-Sensitive Hydrogel through STAT3/REDD1/mTORC1 Cascade

The pathophysiology of osteoarthritis (OA) is closely linked to autophagy abnormalities in articular chondrocytes, the sole mature cell type in healthy cartilage. Nevertheless, the precise molecular mechanism remains uncertain. Previous research has demonstrated that leptin activates mTORC1 , thereby inhibiting chondrocyte autophagy during the progression of OA. In this study, it is demonstrated that the presence of leptin induces a substantial increase in the expression of STAT3, leading to a notable decrease in REDD1 expression and subsequent phosphorylation of p70S6K, a recognized downstream effector of mTORC1. Conversely, inhibition of leptin yields contrasting effects. Additionally, the potential advantages of utilizing a sustained intra-articular release of a leptin inhibitor (LI) via an injectable, thermosensitive poly(D,L-lactide)-poly(ethylene glycol)-poly(D,L-lactide) (PDLLA-PEG-PDLLA: PLEL) hydrogel delivery system for the purpose of investigating its impact on cartilage repair are explored. The study conducted on LI-loaded PLEL (PLEL@LI) demonstrates remarkable efficacy in inhibiting OA and displays encouraging therapeutic advantages in the restoration of subchondral bone and cartilage. These findings establish a solid foundation for the advancement of a pioneering treatment approach utilizing PLEL@LI for OA.

Toward diagnostic relevance of the αVβ5, αVβ3, and αVβ6 integrins in OA: expression within human cartilage and spinal osteophytes

We previously reported 18FPRGD2 uptake by the coxofemoral lining, intervertebral discs and facet joint osteophytes in OA using PET/SCAN imaging. However, the molecular mechanism by which the PRGD2 tracer interacts with joint tissues and osteophytes in OA remains unclear. As PRGD2 ligands are expected to belong to the RGD-specific integrin family, the purpose of this study was (i) to determine which integrin complexes display the highest affinity for PRGD2-based ligands, (ii) to analyze integrin expression in relevant tissues, and (iii) to test integrin regulation in chondrocytes using OA-related stimuli to increase the levels of fibrosis and ossification markers. To this end, the affinity of PRGD2-based ligands for five heterodimeric integrins was measured by competition with 125I-echistatin. In situ analyses were performed in human normal vs. OA cartilage and spinal osteophytes. Osteophytes were characterized by (immuno-)histological staining. Integrin subunit expression was tested in chondrocytes undergoing dedifferentiation, osteogenic differentiation, and inflammatory stimulation. The integrins αVβ5, αVβ3, and αVβ6 presented the highest affinity for PRGD2-based ligands. In situ, the expression of these integrins was significantly increased in OA compared to normal cartilage. Within osteophytes, the mean integrin expression score was significantly higher in blood vessels, fibrous areas, and cells from the bone lining than in osteocytes and cartilaginous zones. In vitro, the levels of integrin subunits were significantly increased during chondrocyte dedifferentiation (except for β6), fibrosis, and osteogenic differentiation as well as under inflammatory stimuli. In conclusion, anatomical zones (such as OA cartilage, intervertebral discs, and facet joint osteophytes) previously reported to show PRGD2 ligand uptake in vivo expressed increased levels of αVβ5, αVβ3, and β6 integrins, whose subunits are modulated in vitro by OA-associated conditions that increase fibrosis, inflammation, and osteogenic differentiation. These results suggest that the increased levels of integrins in OA compared to normal tissues favor PRGD2 uptake and might explain the molecular mechanism of OA imaging using the PRGD2-based ligand PET/CT.

Osteoarthritis Is a Low-Grade Inflammatory Disease: Obesity's Involvement and Herbal Treatment

Osteoarthritis (OA) is considered a major cause of disability around the globe. This handicapping disease causes important cartilage and bone alteration that is associated with serious pains and loss of joint function. Despite its frequent association with obesity, the aetiology of OA is not fully understood. In this review, the different aspects of OA and its correlation with obesity were analysed. Through examining different mechanisms by which obesity may trigger and/or exacerbate OA, we point out some relevant signalling pathways that may evolve as candidates for pharmacological drug development. As such, we also suggest a review of different herbal medicines (HMs) and their main compounds, which specifically interfere with the identified pathways. We have shown that obesity's involvement in OA is not only limited to the mechanical weight exerted on the joints (mechanical hypothesis), but also induces an inflammatory state by different mechanisms, including increased leptin expression, compromised gut mucosa, and/or gut microbiota disruption. The main signalling pathways involved in OA inflammation, which are associated with obesity, are protein tyrosine phosphatase 1B (PTP1B) and TLR4 or DAP12. Moreover, we also underline the contamination of plant extracts with LPS as an important factor to consider when studying HM's effects on articular cells. By summarizing recent publications, this review aims at highlighting newly established aspects of obesity involvement in OA other than the mechanical one.

Insights into intestinal regeneration signaling mechanisms

The cellular mechanisms underlying the amazing ability of sea cucumbers to regenerate their autotomized intestines have been widely described by us and others. However, the signaling pathways that control these mechanisms are unknown. Previous studies have shown that Wnt homologs are upregulated during early intestinal regenerative stages, suggesting that the Wnt/β-catenin pathway is active during this process. Here, we used small molecules, putative disruptors of the Wnt pathway, to determine the potential role of the canonical Wnt pathway on intestine regeneration in the sea cucumber Holothuria glaberrima. We evaluated their effects in vivo by using histological analyses for cell dedifferentiation, cell proliferation and apoptosis. We found that iCRT14, an alleged Wnt pathway inhibitor, decreased the size of the regenerating intestine, while LiCl, a presumed Wnt pathway activator, increased its size. The possible cellular mechanisms by which signaling pathway disruptors affect the gut rudiment size were further studied in vitro, using cultures of tissue explants and additional pharmacological agents. Among the tested signaling activators, those that act through GSK-3 inhibition, LiCl, 1-Azakenpaullone, and CHIR99021 were found to increase muscle cell dedifferentiation, while the inhibitor iCRT14 blocked cell dedifferentiation. Differently, cell proliferation was reduced by all GSK-3 inhibitors, as well as by iCRT14 and C59, which interferes with Wnt ligand secretion. The in vivo temporal and spatial pattern of β-catenin activity was determined using an antibody against phosphorylated β-catenin and shown to correlate with cell proliferative activity. In vitro treatment using C59 decreased the number of cells immunostained for nuclear phosphorylated β-catenin. Our results showed that the cell dedifferentiation observed during intestinal regeneration can be decoupled from the cell proliferation event and that these cellular processes can be modulated by particular signaling pathway inhibitors and activators. These results open the door for future studies where the cellular signaling pathways involved at each regeneration stage can be determined.

CEMIP (KIAA1199) induces a fibrosis-like process in osteoarthritic chondrocytes

CEMIP (for "Cell migration-inducing protein" also called KIAA1199 and Hybid for "Hyaluronan-binding protein") expression is increased in cancers and described as a regulator of cell survival, growth and invasion. In rheumatoid arthritis, CEMIP is referred to as an angiogenic marker and participates in hyaluronic acid degradation. In this study, CEMIP expression is investigated in healthy and osteoarthritis (OA) cartilage from human and mouse. Its role in OA physiopathology is deciphered, specifically in chondrocytes proliferation and dedifferentiation and in the extracellular matrix remodeling. To this end, CEMIP, αSMA and types I and III collagen expressions were assessed in human OA and non-OA cartilage. CEMIP expression was also investigated in a mouse OA model. CEMIP expression was studied in vitro using a chondrocyte dedifferentiation model. High-throughput RNA sequencing was performed on chondrocytes after CEMIP silencing. Results showed that CEMIP was overexpressed in human and murine OA cartilage and along chondrocytes dedifferentiation. Most of genes deregulated in CEMIP-depleted cells were involved in cartilage turnover (e.g., collagens), mesenchymal transition and fibrosis. CEMIP regulated β-catenin protein level. Moreover, CEMIP was essential for chondrocytes proliferation and promoted αSMA expression, a fibrosis marker, and TGFβ signaling towards the p-Smad2/3 (Alk5/PAI-1) pathway. Interestingly, CEMIP was induced by the pSmad1/5 (Alk1) pathway. αSMA and type III collagen expressions were overexpressed in human OA cartilage and along chondrocytes dedifferentiation. Finally, CEMIP was co-expressed in situ with αSMA in all OA cartilage layers. In conclusion, CEMIP was sharply overexpressed in human and mouse OA cartilage and along chondrocytes dedifferentiation. CEMIP-regulated transdifferentiation of chondrocytes into "chondro-myo-fibroblasts" expressing α-SMA and type III collagen, two fibrosis markers. Moreover, these "chondro-myo-fibroblasts" were found in OA cartilage but not in healthy cartilage.

Insights on Molecular Mechanisms of Chondrocytes Death in Osteoarthritis

Osteoarthritis (OA) is a joint pathology characterized by progressive cartilage degradation. Medical care is mainly based on alleviating pain symptoms. Compelling studies report the presence of empty lacunae and hypocellularity in cartilage with aging and OA progression, suggesting that chondrocyte cell death occurs and participates to OA development. However, the relative contribution of apoptosis per se in OA pathogenesis appears complex to evaluate. Indeed, depending on technical approaches, OA stages, cartilage layers, animal models, as well as in vivo or in vitro experiments, the percentage of apoptosis and cell death types can vary. Apoptosis, chondroptosis, necrosis, and autophagic cell death are described in this review. The question of cell death causality in OA progression is also addressed, as well as the molecular pathways leading to cell death in response to the following inducers: Fas, Interleukin-1β (IL-1β), Tumor Necrosis factor-α (TNF-α), leptin, nitric oxide (NO) donors, and mechanical stresses. Furthermore, the protective role of autophagy in chondrocytes is highlighted, as well as its decline during OA progression, enhancing chondrocyte cell death; the transition being mainly controlled by HIF-1α/HIF-2α imbalance. Finally, we have considered whether interfering in chondrocyte apoptosis or promoting autophagy could constitute therapeutic strategies to impede OA progression.