Bioreactor-Controlled Physoxia Regulates TGF-β Signaling to Alter Extracellular Matrix Synthesis by Human Chondrocytes

Differential impact of chronic intermittent hypoxia and stress changes on condylar development

OBJECTIVES

This study aimed to determine the effects of chronic intermittent hypoxia (CIH) and stress change (SC) on the development of the condyle in mouth breathing rats.

DESIGN

A total of 120 4-week-old rats were randomly assigned to one of five groups. The control (Ctrl) group was the blank control and the intermittent nasal obstruction (INO) group was the positive control. Mild CIH (mCIH) and severe CIH (sCIH) groups were developed by adjusting environmental oxygen concentration and monitoring real-time blood oxygen saturation (SpO2). The SC group was developed using INO, increased environmental oxygen concentration, and real-time SpO2 monitoring. Six rats from each group were sacrificed for analysis at 0, 1, 2, or 4 weeks.

RESULTS

Similar to the INO group, condyle and mandibular body development in the sCIH group, but not in the mCIH group, was significantly inhibited compared with the Ctrl group. The SC group had inhibited development of the condyle, especially of the posterior zone, but had minimal impact on the growth of the mandible.

CONCLUSION

The inhibitory effects of CIH on the development of the condyle and mandibular body were SpO2-dose-dependent. When SC occurred, inhibited development was observed in the posterior zone of condyle but not the whole mandible. These findings provide important insights for targeted interventions that address the consequences of mouth breathing in children.

SIRT3 alleviates high glucose-induced chondrocyte injury through the promotion of autophagy and suppression of apoptosis in osteoarthritis progression

A growing amount of epidemiological evidence proposes diabetes mellitus (DM) to be an independent risk factor for osteoarthritis (OA). Sirtuin 3 (SIRT3), which is mainly located in mitochondria, belongs to the family of nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases and is involved in the physiological and pathological processes of cell regulation. The aim of this study was to investigate the effects of SIRT3 on diabetic OA and underlying mechanisms in the prevention of type 2 DM (T2DM)-induced articular cartilage damage. High-fat and high-sugar diets combined with streptozotocin (STZ) injection were used for establishing an experimental T2DM rat model. The destabilization of medial meniscus (DMM) surgery was applied to induce the rat OA model. Primary rat chondrocytes were cultivated with a concentration of gradient glucose. Treatment with intra-articular injection of SIRT3 overexpression lentivirus was achieved in vivo, and intervention with SIRT3 knockdown was performed using siRNA transfection in vitro. High glucose content was found to activate inflammatory response, facilitate apoptosis, downregulate autophagy, and exacerbate mitochondrial dysfunction in a dose-dependent manner in rat chondrocytes, which can be deteriorated by SIRT3 knockdown. In addition, articular cartilage damage was found to be more severe in T2DM-OA rats than in DMM-induced OA rats, which can be mitigated by the intra-articular injection of SIRT3 overexpression lentivirus. Targeting SIRT3 is a potential therapeutic strategy for the alleviation of diabetic OA.

Photobiomodulation inhibits the expression of chondroitin sulfate proteoglycans after spinal cord injury via the Sox9 pathway

Both glial cells and glia scar greatly affect the development of spinal cord injury and have become hot spots in research on spinal cord injury treatment. The cellular deposition of dense extracellular matrix proteins such as chondroitin sulfate proteoglycans inside and around the glial scar is known to affect axonal growth and be a major obstacle to autogenous repair. These proteins are thus candidate targets for spinal cord injury therapy. Our previous studies demonstrated that 810 nm photobiomodulation inhibited the formation of chondroitin sulfate proteoglycans after spinal cord injury and greatly improved motor function in model animals. However, the specific mechanism and potential targets involved remain to be clarified. In this study, to investigate the therapeutic effect of photobiomodulation, we established a mouse model of spinal cord injury by T9 clamping and irradiated the injury site at a power density of 50 mW/cm2 for 50 minutes once a day for 7 consecutive days. We found that photobiomodulation greatly restored motor function in mice and downregulated chondroitin sulfate proteoglycan expression in the injured spinal cord. Bioinformatics analysis revealed that photobiomodulation inhibited the expression of proteoglycan-related genes induced by spinal cord injury, and versican, a type of proteoglycan, was one of the most markedly changed molecules. Immunofluorescence staining showed that after spinal cord injury, versican was present in astrocytes in spinal cord tissue. The expression of versican in primary astrocytes cultured in vitro increased after inflammation induction, whereas photobiomodulation inhibited the expression of versican. Furthermore, we found that the increased levels of p-Smad3, p-P38 and p-Erk in inflammatory astrocytes were reduced after photobiomodulation treatment and after delivery of inhibitors including FR 180204, (E)-SIS3, and SB 202190. This suggests that Smad3/Sox9 and MAPK/Sox9 pathways may be involved in the effects of photobiomodulation. In summary, our findings show that photobiomodulation modulates the expression of chondroitin sulfate proteoglycans, and versican is one of the key target molecules of photobiomodulation. MAPK/Sox9 and Smad3/Sox9 pathways may play a role in the effects of photobiomodulation on chondroitin sulfate proteoglycan accumulation after spinal cord injury.

Human Chondrocytes, Metabolism of Articular Cartilage, and Strategies for Application to Tissue Engineering

Hyaline cartilage, which is characterized by the absence of vascularization and innervation, has minimal self-repair potential in case of damage and defect formation in the chondral layer. Chondrocytes are specialized cells that ensure the synthesis of extracellular matrix components, namely type II collagen and aggregen. On their surface, they express integrins CD44, α1β1, α3β1, α5β1, α10β1, αVβ1, αVβ3, and αVβ5, which are also collagen-binding components of the extracellular matrix. This article aims to contribute to solving the problem of the possible repair of chondral defects through unique methods of tissue engineering, as well as the process of pathological events in articular cartilage. In vitro cell culture models used for hyaline cartilage repair could bring about advanced possibilities. Currently, there are several variants of the combination of natural and synthetic polymers and chondrocytes. In a three-dimensional environment, chondrocytes retain their production capacity. In the case of mesenchymal stromal cells, their favorable ability is to differentiate into a chondrogenic lineage in a three-dimensional culture.

Electroacupuncture Exerts Chondroprotective Effect in Knee Osteoarthritis of Rabbits Through the Mitophagy Pathway

Purpose

Mitochondrial dysfunction of chondrocytes has become an area of focus in Knee Osteoarthritis (KOA) in recent years. Activation of mitophagy could promote the survival of chondrocytes and alleviate cartilage degeneration. The aim of this study was to explore whether mitophagy was involved in the cartilage protection of KOA rabbits after electroacupuncture (EA) intervention.

Methods

The rabbits were divided into 3 groups, Control group, KOA group, EA group, with 6 rabbits in each group. KOA model rabbits were established by modified Videman's extended immobilization method for 6 weeks and randomly divided into KOA group and EA group. The rabbits in EA group were treated every other day for 3 weeks. The degree of cartilage degeneration was detected by Safranine O-Fast Green staining and immunofluorescence. The morphological changes of chondrocytes mitochondria were detected by transmission electron microscope. ATP concentration in cartilage was measured by ATP Assay Kit. The changes of Pink1-Parkin signal pathway were detected by immunofluorescence, Western blot, and Real-time PCR.

Results

The morphology showed that EA could reduce the degeneration of KOA cartilage and increase the distribution of collagen II. We also found that EA could activate mitophagy in KOA rabbit chondrocytes to remove damaged mitochondria and restore mitochondrial homeostasis, which was manifested as increasing the expression of LC3 II/I, promoting the colocalization of TOM20 and LC3B, reducing the accumulation of mitochondrial markers outer mitochondrial membrane 20 (TOM20) and inner mitochondrial membrane 23 (TIM23), and increasing ATP production in chondrocytes. This regulation might be achieved by upregulating the Pink1-Parkin signal pathway.

Conclusion

EA may play a role in protecting KOA cartilage by activating mitophagy mediated through Pink1-Parkin pathway.

Construction of Rapid Extracellular Matrix-Deposited Small-Diameter Vascular Grafts Induced by Hypoxia in a Bioreactor

Cardiovascular disease has become one of the most globally prevalent diseases, and autologous or vascular graft transplantation has been the main treatment for the end stage of the disease. However, there are no commercialized small-diameter vascular graft (SDVG) products available. The design of SDVGs is promising in the future, and SDVG preparation using an in vitro bioreactor is a favorable method, but it faces the problem of long-term culture of >8 weeks. Herein, we used different oxygen (O₂) concentrations and mechanical stimulation to induce greater secretion of extracellular matrix (ECM) from cells in vitro to rapidly prepare SDVGs. Culturing with 2% O₂ significantly increased the production of the ECM components and growth factors of human dermal fibroblasts (hDFs). To accelerate the formation of ECM, hDFs were seeded on a polycaprolactone (PCL) scaffold and cultured in a flow culture bioreactor with 2% O₂ for only 3 weeks. After orthotopic transplantation in rat abdominal aorta, the cultured SDVGs (PCL-decellularized ECM) showed excellent endothelialization and smooth muscle regeneration. The vascular grafts cultured with hypoxia and mechanical stimulation could accelerate the reconstruction speed and obtain an improved therapeutic effect and thereby provide a new research direction for improving the production and supply of SDVGs.

Physosmotic Induction of Chondrogenic Maturation Is TGF-β Dependent and Enhanced by Calcineurin Inhibitor FK506

Increasing extracellular osmolarity 100 mOsm/kg above plasma level to the physiological levels for cartilage induces chondrogenic marker expression and the differentiation of chondroprogenitor cells. The calcineurin inhibitor FK506 has been reported to modulate the hypertrophic differentiation of primary chondrocytes under such conditions, but the molecular mechanism has remained unclear. We aimed at clarifying its role. Chondrocyte cell lines and primary cells were cultured under plasma osmolarity and chondrocyte-specific in situ osmolarity (+100 mOsm, physosmolarity) was increased to compare the activation of nuclear factor of activated T-cells 5 (NFAT5). The effects of osmolarity and FK506 on calcineurin activity, cell proliferation, extracellular matrix quality, and BMP- and TGF-β signaling were analyzed using biochemical, gene, and protein expression, as well as reporter and bio-assays. NFAT5 translocation was similar in chondrocyte cell lines and primary cells. High supraphysiological osmolarity compromised cell proliferation, while physosmolarity or FK506 did not, but in combination increased proteoglycan and collagen expression in chondrocytes in vitro and in situ. The expression of the TGF-β-inducible protein TGFBI, as well as chondrogenic (SOX9, Col2) and terminal differentiation markers (e.g., Col10) were affected by osmolarity. Particularly, the expression of minor collagens (e.g., Col9, Col11) was affected. The inhibition of the FK506-binding protein suggests modulation at the TGF-β receptor level, rather than calcineurin-mediated signaling, as a cause. Physiological osmolarity promotes terminal chondrogenic differentiation of progenitor cells through the sensitization of the TGF-β superfamily signaling at the type I receptor. While hyperosmolarity alone facilitates TGF-β superfamily signaling, FK506 further enhances signaling by releasing the FKBP12 break from the type I receptor to improve collagenous marker expression. Our results help explain earlier findings and potentially benefit future cell-based cartilage repair strategies.

Osteochondral regeneration in rabbit using xenograft decellularized ECM in combination with different biological products; platelet-rich fibrin, amniotic membrane extract, and mesenchymal stromal cells

This study aimed to investigate the regenerative effect of decellularized osteochondral ECM xenograft in combination with various biological products in an osteochondral (OC) defect. OC tissue from the sheep femur were obtained and decellularized. The decellularized ECM (dECM) was combined with either platelet-rich fibrin (PRF), amniotic membrane extract (AME), or rabbit bone marrow-derived mesenchymal stromal cells (rBMSCs). The hybrid dECM-biological products were then utilized for the treatment of rabbit OC critical size defects. The regenerative potential of different groups was compared using; MRI, macroscopic assessment, histopathology, and histomorphometry. All characterizations analysis verified successful decellularization. Three months post-surgery, macroscopic findings indicated that dECM was better compared to controls. Also, dECM in combination with AME, PRF, and rBMSCs showed enhanced OC regeneration compared to only dECM (AME: +100%, PRF: +61%, rBMSCs: +28%). In particular, the dECM+AME group results in the best integration of new cartilage into surrounding cartilage tissue. The histomorphometric evaluations demonstrated enhancement in new cartilage formation and bone tissue (86.5 ± 5.9% and 90 ± 7.7%, respectively) for the dECM+AME group compared to other groups. Furthermore, histological results for the dECM+AME elucidated a mature hyaline cartilage tissue that covered the new and symmetrically formed subchondral bone, exhibiting a significantly higher regenerative effect compared to all other treated groups. This finding was also confirmed with MRI images. The current study revealed that in addition to the benefits of dECM alone, its combination with AME indicated to have a superior regenerative effect on OC regeneration. Overall, dECM+AME may be considered a suitable construct for treating knee OC injuries.

Biochemical Aspects of Scaffolds for Cartilage Tissue Engineering; from Basic Science to Regenerative Medicine

Chondral defects are frequent and important causes of pain and disability. Cartilage has limited self-repair and regeneration capacity. The ideal approach for articular cartilage defects is the regeneration of hyaline cartilage with sustainable symptom-free constructs. Tissue engineering provides new strategies for the regeneration of functional cartilage tissue through optimized scaffolds with architectural, mechanical, and biochemical properties similar to the native cartilage tissue. In this review, the basic science of cartilage structure, interactions between proteins, stem cells, as well as biomaterials, scaffold characteristics and fabrication methods, as well as current and potential therapies in regenerative medicine will be discussed mostly from a biochemical point of view. Furthermore, the recent trends in scaffold-based therapies and supplementary factors in cartilage tissue engineering will be considered.

Nrf2/ARE Signaling Directly Regulates SOX9 to Potentially Alter Age-Dependent Cartilage Degeneration

Oxidative stress is implicated in osteoarthritis, and nuclear factor erythroid 2–related factor 2 (Nrf2)/antioxidant response element (ARE) pathway maintains redox homeostasis. We investigated whether Nrf2/ARE signaling controls SOX9. SOX9 expression in human C-28/I2 chondrocytes was measured by RT–qPCR after shRNA-mediated knockdown of Nrf2 or its antagonist the Kelch-like erythroid cell-derived protein with cap ‘‘n’’ collar homology-associated protein 1 (Keap1). To verify whether Nrf2 transcriptionally regulates SOX9, putative ARE-binding sites in the proximal SOX9 promoter region were inactivated, cloned into pGL3, and co-transfected with phRL–TK for dual-luciferase assays. SOX9 promoter activities without and with Nrf2-inducer methysticin were compared. Sox9 expression in articular chondrocytes was correlated to cartilage thickness and degeneration in wild-type (WT) and Nrf2-knockout mice. Nrf2-specific RNAi significantly decreased SOX9 expression, whereas Keap1-specific RNAi increased it. Putative ARE sites (ARE1, ARE2) were identified in the SOX9 promoter region. ARE2 mutagenesis significantly reduced SOX9 promoter activity, but ARE1 excision did not. Functional ARE2 site was essential for methysticin-mediated induction of SOX9 promoter activity. Young Nrf2-knockout mice revealed significantly lower Sox9-positive chondrocytes, and old Nrf2-knockout animals showed thinner cartilage and more cartilage degeneration. Our results suggest Nrf2 directly regulates SOX9 in articular cartilage, and Nrf2-loss can develop mild osteoarthritis at old age. Pharmacological Nrf2 induction may hold the potential to diminish age-dependent cartilage degeneration through improving SOX9 expression.

Cartilage Repair Using Clematis Triterpenoid Saponin Delivery Microcarrier, Cultured in a Microgravity Bioreactor Prior to Application in Rabbit Model

Cartilage tissue engineering provides a promising method for the repair of articular cartilage defects, requiring appropriate biological scaffolds and necessary growth factors to enhance the efficiency of cartilage regeneration. Here, a silk fibroin (SF) microcarrier and a clematis triterpenoid saponin delivery SF (CTS-SF) microcarrier were prepared by the high-voltage electrostatic differentiation and lyophilization method, and chondrocytes were carried under the simulated microgravity condition by a rotating cell culture system. SF and CTS-SF microspheres were relatively uniform in size and had a porous structure with good swelling and cytocompatibility. Further, CTS-SF microcarriers could sustainably release CTSs in the monitored 10 days. Compared with the monolayer culture, chondrocytes under the microgravity condition maintained a better chondrogenic phenotype and showed better proliferation ability after culture on microcarriers. Moreover, the sustained release of CTS from CTS-SF microcarriers upregulated transforming growth factor-β, Smad2, and Smad3 signals, contributing to promote chondrogenesis. Hence, the biophysical effects of microgravity and bioactivities of CTS-ST were used for chondrocyte expansion and phenotype maintenance in vitro. With prolonged expansion, SF- and CTS-SF-based microcarrier-cell composites were directly implanted in vivo to repair rabbit articular defects. Gross evaluations, histopathological examinations, and biochemical analysis indicated that SF- and CTS-SF-based composites exhibited cartilage-like tissue repair compared with the nontreated group. Further, CTS-SF-based composites displayed superior hyaline cartilage-like repair that integrated with the surrounding cartilage better and higher cartilage extracellular matrix content. In conclusion, these results provide an alternative preparation method for drug-delivered SF microcarrier and a culture method for maintaining the chondrogenic phenotype of seed cells based on the microgravity environment. CTS showed its bioactive function, and the application of CTS-SF microcarriers can help repair and regenerate cartilage defects.

The Attenuating Effect of Low-Intensity Pulsed Ultrasound on Hypoxia-Induced Rat Chondrocyte Damage in TMJ Osteoarthritis Based on TMT Labeling Quantitative Proteomic Analysis

Temporomandibular joint osteoarthritis (TMJOA) is a degenerative disease with a complex and multifactorial etiology. An increased intrajoint pressure or weakened penetration can exacerbate the hypoxic state of the condylar cartilage microenvironment. Our group previously simulated the hypoxic environment of TMJOA in vitro. Low-intensity pulsed ultrasound (LIPUS) stimulation attenuates chondrocyte matrix degradation via a hypoxia-inducible factor (HIF) pathway-associated mechanism, but the mode of action of LIPUS is currently poorly understood. Moreover, most recent studies investigated the pathological mechanisms of osteoarthritis, but no biomarkers have been established for assessing the therapeutic effect of LIPUS on TMJOA with high specificity, which results in a lack of guidance regarding clinical application. Here, tandem mass tag (TMT)-based quantitative proteomic technology was used to comprehensively screen the molecular targets and pathways affected by the action of LIPUS on chondrocytes under hypoxic conditions. A bioinformatic analysis identified 902 and 131 differentially expressed proteins (DEPs) in the <1% oxygen treatment group compared with the control group and in the <1% oxygen + LIPUS stimulation group compared with the <1% oxygen treatment group, respectively. The DEPs were analyzed by gene ontology (GO), KEGG pathway and protein-protein interaction (PPI) network analyses. By acting on extracellular matrix (ECM)-associated proteins, LIPUS increases energy production and activates the FAK signaling pathway to regulate cell biological behaviors. DEPs of interest were selected to verify the reliability of the proteomic results. In addition, this experiment demonstrated that LIPUS could upregulate chondrogenic factors (such as Sox9, Collagen Ⅱ and Aggrecan) and increase the mucin sulfate content. Moreover, LIPUS reduced the hydrolytic degradation of the ECM by decreasing the MMP3/TIMP1 ratio and vascularization by downregulating VEGF. Interestingly, LIPUS improved the migration ability of chondrocytes. In summary, LIPUS can regulate complex biological processes in chondrocytes under hypoxic conditions and alter the expression of many functional proteins, which results in reductions in hypoxia-induced chondrocyte damage. ECM proteins such as thrombospondin4, thrombospondin1, IL1RL1, and tissue inhibitors of metalloproteinase 1 play a central role and can be used as specific biomarkers determining the efficacy of LIPUS and viable clinical therapeutic targets of TMJOA.

Strategies to Modulate the Redifferentiation of Chondrocytes

Because of the low self-healing capacity of articular cartilage, cartilage injuries and degenerations triggered by various diseases are almost irreversible. Previous studies have suggested that human chondrocytes cultured in vitro tend to dedifferentiate during the cell-amplification phase and lose the physiological properties and functions of the cartilage itself, which is currently a critical limitation in the cultivation of cartilage for tissue engineering. Recently, numerous studies have focused on the modulation of chondrocyte redifferentiation. Researchers discovered the effect of various conditions (extracellular environment, cell sources, growth factors and redifferentiation inducers, and gene silencing and overexpression) on the redifferentiation of chondrocytes during the in vitro expansion of cells, and obtained cartilage tissue cultured in vitro that exhibited physiological characteristics and functions that were similar to those of human cartilage tissue. Encouragingly, several studies reported positive results regarding the modulation of the redifferentiation of chondrocytes in specific conditions. Here, the various factors and conditions that modulate the redifferentiation of chondrocytes, as well as their limitations and potential applications and challenges are reviewed. We expect to inspire research in the field of cartilage repair toward the future treatment of arthropathy.

Baicalin promotes chondrocyte viability and the synthesis of extracellular matrix through TGF-β/Smad3 pathway in chondrocytes

BACKGROUND

Osteoarthritis (OA) is common in the elderly. Baicalin (BA) is a flavonoid monomer extracted from Scutellaria baicalensis Georgi, which has been reported to have anti-inflammatory, anti-deformation and anti-bacterial effects.

METHODS

Cultures of micromass and 3D alginate beads, Alcian blue and Safranin O (SO)/fast green staining were used to investigate chondrocyte viability and extracellular matrix (ECM) synthesis in chondrocytes of all groups. The expression of SOX9, Smad3, Aggrecan (ACAN), type II collagen (Col2α), matrix metallopetidase 9 (MMP9), MMP13 and ADAMTS5 in chondrocytes of all groups were detected by western blot or qRT-PCR.

RESULTS

The present study demonstrates that BA neutralized the IL-1β-induced downregulation of chondrocyte viability and ECM secretion, including ACAN and Col2α. The downregulation of SOX9, and the upregulation of MMP9, MMP13 and ADAMTS5 induced by IL-1β were reversed by BA treatment. Moreover, BA increased the nuclear translocation of Smad3 and SOX9 in chondrocytes cultured by micromass and 3D alginate beads. Interestingly, Smad3 inhibitor SIS3 reversed the promoting effect of BA on chondrocyte viability, ECM secretion, SOX9 and Smad3 nuclear translocation, and the inhibiting effect of BA on MMP9 and ADAMTS5 expressions. BA treatment also attenuated the decrease of Smad3 phosphorylation, SOX9 expression and the damage of cartilage integrity in mice which were induced by destabilization of the medial meniscus (DMM).

CONCLUSION

BA promotes chondrocyte viability and the cell matrix synthesis through TGF-β/Smad3 pathway in IL-1β-treated chondrocytes and DMM treated mice. BA is a potential therapeutic target for OA.

Thoughts on cartilage tissue engineering: A 21st century perspective

In mature individuals, hyaline cartilage demonstrates a poor intrinsic capacity for repair, thus even minor defects could result in progressive degeneration, impeding quality of life. Although numerous attempts have been made over the past years for the advancement of effective treatments, significant challenges still remain regarding the translation of in vitro cartilage engineering strategies from bench to bedside. This paper reviews the latest concepts on engineering cartilage tissue in view of biomaterial scaffolds, tissue biofabrication, mechanobiology, as well as preclinical studies in different animal models. The current work is not meant to provide a methodical review, rather a perspective of where the field is currently focusing and what are the requirements for bridging the gap between laboratory-based research and clinical applications, in light of the current state-of-the-art literature. While remarkable progress has been accomplished over the last 20 years, the current sophisticated strategies have reached their limit to further enhance healthcare outcomes. Considering a clinical aspect together with expertise in mechanobiology, biomaterial science and biofabrication methods, will aid to deal with the current challenges and will present a milestone for the furtherance of functional cartilage engineering.

Chondrogeneic Potential of MSC from Different Sources in Spheroid Culture

We performed a comparative study of the proliferative potential of human mesenchymal stromal cells (MSC) from three sources (tooth pulp, adipose tissue, and Wharton's jelly) in spheroid culture; human chondroblasts served as the positive control. Histological examination revealed signs of chondrogenic differentiation in all studied cell cultures and the differences in the volume and composition of the extracellular matrix. Spheroids formed by MSC from the tooth pulp and Wharton's jelly were characterized by low content of extracellular matrix and glycosaminoglycans. Spheroids from adipose tissue MSC contained maximum amount of the extracellular matrix and high content of glycosaminoglycans. Chondrocytes produced glycosaminoglycan-enriched matrix. Type II collagen was produced by chondrocytes (to a greater extent) and adipose tissue MSC (to a lesser extent). The results of our study demonstrate that MSC from the adipose tissue under conditions of spheroid culturing exhibited maximum chondrogenic potential.

Mechanistic insights into AMPK-SIRT3 positive feedback loop-mediated chondrocyte mitochondrial quality control in osteoarthritis pathogenesis

Osteoarthritis (OA) is a major cause of disability in the elderly population and represents a significant public health problem and socioeconomic burden worldwide. However, no disease-modifying therapeutics are currently available for OA due to an insufficient understanding of the pathogenesis of this disability. As a unique cell type in cartilage, chondrocytes are essential for cartilage homeostasis and play a critical role in OA pathogenesis. Mitochondria are important metabolic centers in chondrocytes and contribute to cell survival, and mitochondrial quality control (MQC) is an emerging mechanism for maintaining cell homeostasis. An increasing number of recent studies have demonstrated that dysregulation of the key processes of chondrocyte MQC, which involve mitochondrial redox, biogenesis, dynamics, and mitophagy, is associated with OA pathogenesis and can be regulated by the chondroprotective molecules 5' adenosine monophosphate-activated protein kinase (AMPK) and sirtuin 3 (SIRT3). Moreover, AMPK and SIRT3 regulate each other, and their expression and activity are always consistent in chondrocytes, which suggests the existence of an AMPK-SIRT3 positive feedback loop (PFL). Although the precise mechanisms are not fully elucidated and need further validation, the current literature indicates that this AMPK-SIRT3 PFL regulates OA development and progression, at least partially by mediating chondrocyte MQC. Therefore, understanding the mechanisms of AMPK-SIRT3 PFL-mediated chondrocyte MQC in OA pathogenesis might yield new ideas and potential targets for subsequent research on the OA pathomechanism and therapeutics.

Varying development of femoral and tibial subchondral bone tissue and their interaction with articular cartilage during progressing osteoarthritis

INTRODUCTION

Differences between tibial and femoral joint surfaces and knee compartments concerning coupled bone and cartilage turnover or bone-cartilage cross talk have not been previously examined, although the mechanical and biological interaction of the mineralized subchondral tissues with articular cartilage is of great importance for advancing osteoarthritis.

MATERIALS AND METHODS

Therefore, with the help of immunohistochemistry and real-time polymerase chain reaction (RT-PCR), human knee joint cartilage tissue was investigated for expression of key molecules of the extracellular matrix and cartilage composition (collagen type I and II, aggrecan) plus proteoglycan content (colorimetric analysis). Furthermore, we correlated the results with 3D microcomputed tomography of the underlying subchondral bone (high-resolution micro-CT system). Measurements were performed in dependence of the anatomical site (femoral vs. tibial, medial and lateral each) to identify regional differences during the osteoarthritic process. From an enduring series of 108 patients undergoing implantation of TKA, 34 osteochondral samples with lesions macroscopically classified as ICRS grade 1b (group A) and 34 samples with ICRS grade 3a/3b lesions (group B) were compared with 21 healthy controls.

RESULTS

Concerning 3D analysis, the medial femoral condyle and tibia showed the most significant increase in bone volume fraction and a decrease in the trabecular number in group B frequently accompanied by subchondral bone resorption pits and enchondral ossification. Under physiological conditions, tibia plateaus show lower bone volume fraction than the corresponding femoral site and this difference enlarges with advancing OA. Partially even contradictory behavior was observed such as trabecular separation at the lateral tibial and medial plateau in osteochondral OA samples of the same patients. Collagen type II expression levels show faster and varying changes than type I during the OA process, leading to a lower positive or negative correlation with bone microstructural analysis, especially on the tibia plateau.

CONCLUSIONS

Structural bone and cartilage parameter changes showed varying developments and correlations among each other in the different compartments of the knee. As a clinical conclusion, therapies to postpone or prevent cartilage degeneration by influencing the loss of mineralized bone could be site dependent.

LncRNA MIR4435-2HG-mediated upregulation of TGF-β1 promotes migration and proliferation of nonsmall cell lung cancer cells

The roles of long noncoding RNAs (lncRNAs) have been shown to play critical roles in tumor progression. Here, it was identified that lncRNA MIR4435-2HG was highly expressed in lung cancer tissues, especially in nonsmall cell lung cancer (NSCLC). A consistent result was obtained in lung cancer cells. Functional experiments showed that knockdown of MIR4435-2HG reduced the proliferation and migration ability of NSCLC cells. Transcriptome-sequencing analysis indicated that TGF-β signaling was mostly enriched in NSCLC cells with MIR4435-2HG knockdown. Furthermore, MIR4435-2HG was identified as an miRNA sponge for TGF-β1 and thus activated TGF-β signaling. Additionally, re-activation of TGF-β1 rescued MIR4435-2HG knockdown-mediated inhibition on the progression of NSCLC cells. Therefore, this work indicates a novel MIR4435-2HG/TGF-β1 axis responsible for NSCLC cell progression.

Exosomes produced from 3D cultures of umbilical cord mesenchymal stem cells in a hollow-fiber bioreactor show improved osteochondral regeneration activity

Animal and clinical studies have shown that mesenchymal stem cells (MSCs) play an important role in cartilage repair. The therapeutic effect of mesenchymal stem cells based therapies has been increasingly demonstrated to exosome-mediated paracrine secretion. Here, we investigated the cellular processes and mechanism of exosomes produced by conventional 2D culture (2D-Exos) and exosomes produced from 3D culture (3D-Exos) of umbilical MSCs (U-MSCs) in a hollow-fiber bioreactor for the treatment of cartilage repair. We found that the yield of 3D-Exos was 7.5-fold higher than that of 2D-Exos. The in vitro experiments indicated that both 2D-Exos and 3D-Exos can stimulate chondrocyte proliferation, migration, and matrix synthesis, and inhibit apoptosis, with 3D-Exos exerting a stronger effect than 2D-Exos. This effect was partly attributed to the activation of transforming growth factor beta 1 and Smad2/3 signaling. The injection of 2D-Exos and 3D-Exos showed enhanced gross appearance and attenuated cartilage defect; however, 3D-Exos showed a superior therapeutic effect than 2D-Exos. In summary, our study provides novel insights into the chondroprotective effects of exosomes produced from 3D culture of U-MSCs in a hollow-fiber bioreactor. Because of its promising biological function and high yield, 3D-Exos may become a promising therapeutic method for the treatment of cartilage defects.