Cyclic Tensile Strain Upregulates Pro-Inflammatory Cytokine Expression Via FAK-MAPK Signaling in Chondrocytes

Weight change patterns across adulthood are associated with the risk of osteoarthritis: a population-based study

BACKGROUND

Body weight has been recognized as a driving factor of osteoarthritis. Few studies had investigated the association between weight status across adulthood and risk of osteoarthritis (OA). This study investigates the association of weight change patterns across adulthood (lasting at least 25 years) with the risk of OA from the National Health and Nutrition Examination Survey (NHANES) 2013-2018.

METHODS

The study assessed the relationship between weight change across adulthood and OA in 7392 individuals aged > 50 spanning a minimum of 25 years. Multivariate linear regression analyses were utilized to detect the association between weight change patterns and self-reported OA. Restricted cubic splines (RCS) were used to examine the nonlinear relationship between absolute weight change and OA risk.

RESULTS

From 10 years ago to survey, the risk of OA was 1.34-fold (95% CI 1.07-1.68) in people changed from obese to non-obese, 1.61-fold (95% CI 1.29-2.00) in people change from non-obese to obese, and 1.82-fold (95% CI 1.49-2.22) in stable obese people compared with people who were at stable normal weight. Similar patterns were also observed at age 25 years to baseline and age 25 years to 10 years before the baseline. The dose-response association of RCS found a U-shaped relationship between absolute weight change and OA risk.

CONCLUSIONS

The study suggests that weight patterns across adulthood are associated with the risk of OA. These findings stressed important to maintain a normal weight throughout adulthood, especially to prevent ignored weight gain in early adulthood to reduce OA risk later.

Emerging technology has a brilliant future: the CRISPR-Cas system for senescence, inflammation, and cartilage repair in osteoarthritis

Osteoarthritis (OA), known as one of the most common types of aseptic inflammation of the musculoskeletal system, is characterized by chronic pain and whole-joint lesions. With cellular and molecular changes including senescence, inflammatory alterations, and subsequent cartilage defects, OA eventually leads to a series of adverse outcomes such as pain and disability. CRISPR-Cas-related technology has been proposed and explored as a gene therapy, offering potential gene-editing tools that are in the spotlight. Considering the genetic and multigene regulatory mechanisms of OA, we systematically review current studies on CRISPR-Cas technology for improving OA in terms of senescence, inflammation, and cartilage damage and summarize various strategies for delivering CRISPR products, hoping to provide a new perspective for the treatment of OA by taking advantage of CRISPR technology.

Moderate mechanical stress suppresses chondrocyte ferroptosis in osteoarthritis by regulating NF-κB p65/GPX4 signaling pathway

Ferroptosis is a recently identified form of programmed cell death that plays an important role in the pathophysiological process of osteoarthritis (OA). Herein, we investigated the protective effect of moderate mechanical stress on chondrocyte ferroptosis and further revealed the internal molecular mechanism. Intra-articular injection of sodium iodoacetate (MIA) was conducted to induce the rat model of OA in vivo, meanwhile, interleukin-1 beta (IL-1β) was treated to chondrocytes to induce the OA cell model in vitro. The OA phenotype was analyzed by histology and microcomputed tomography, the ferroptosis was analyzed by transmission electron microscope and immunofluorescence. The expression of ferroptosis and cartilage metabolism-related factors was analyzed by immunohistochemical and Western blot. Animal experiments revealed that moderate-intensity treadmill exercise could effectively reduce chondrocyte ferroptosis and cartilage matrix degradation in MIA-induced OA rats. Cell experiments showed that 4-h cyclic tensile strain intervention could activate Nrf2 and inhibit the NF-κB signaling pathway, increase the expression of Col2a1, GPX4, and SLC7A11, decrease the expression of MMP13 and P53, thereby restraining IL-1β-induced chondrocyte ferroptosis and degeneration. Inhibition of NF-κB signaling pathway relieved the chondrocyte ferroptosis and degeneration. Meanwhile, overexpression of NF-κB by recombinant lentivirus reversed the positive effect of CTS on chondrocytes. Moderate mechanical stress could activate the Nrf2 antioxidant system, inhibit the NF-κB p65 signaling pathway, and inhibit chondrocyte ferroptosis and cartilage matrix degradation by regulating P53, SLC7A11, and GPX4.

Recent Advancement in Elimination Strategies and Potential Rejuvenation Targets of Senescence

Cellular senescence is a state of exiting the cell cycle, resisting apoptosis, and changing phenotype. Senescent cells (SCs) can be identified by large, distorted morphology and irreversible inability to replicate. In early development, senescence has beneficial roles like tissue patterning and wound healing, where SCs are cleared by the immune system. However, there is a steep rise in SC number as organisms age. The issue with SC accumulation stems from the loss of cellular function, alterations of the microenvironment, and secretions of pro-inflammatory molecules, consisting of cytokines, chemokines, matrix metalloproteinases (MMPs), interleukins, and extracellular matrix (ECM)-associated molecules. This secreted cocktail is referred to as the senescence-associated secretory phenotype (SASP), a hallmark of cellular senescence. The SASP promotes inflammation and displays a bystander effect where paracrine signaling turns proliferating cells into senescent states. To alleviate age-associated diseases, researchers have developed novel methods and techniques to selectively eliminate SCs in aged individuals. Although studies demonstrated that selectively killing SCs improves age-related disorders, there are drawbacks to SC removal. Considering favorable aspects of senescence in the body, this paper reviews recent advancements in elimination strategies and potential rejuvenation targets of senescence to bring researchers in the field up to date.

Double-edged role of mechanical stimuli and underlying mechanisms in cartilage tissue engineering

Mechanical stimuli regulate the chondrogenic differentiation of mesenchymal stem cells and the homeostasis of chondrocytes, thus affecting implant success in cartilage tissue engineering. The mechanical microenvironment plays fundamental roles in the maturation and maintenance of natural articular cartilage, and the progression of osteoarthritis Hence, cartilage tissue engineering attempts to mimic this environment in vivo to obtain implants that enable a superior regeneration process. However, the specific type of mechanical loading, its optimal regime, and the underlying molecular mechanisms are still under investigation. First, this review delineates the composition and structure of articular cartilage, indicating that the morphology of chondrocytes and components of the extracellular matrix differ from each other to resist forces in three top-to-bottom overlapping zones. Moreover, results from research experiments and clinical trials focusing on the effect of compression, fluid shear stress, hydrostatic pressure, and osmotic pressure are presented and critically evaluated. As a key direction, the latest advances in mechanisms involved in the transduction of external mechanical signals into biological signals are discussed. These mechanical signals are sensed by receptors in the cell membrane, such as primary cilia, integrins, and ion channels, which next activate downstream pathways. Finally, biomaterials with various modifications to mimic the mechanical properties of natural cartilage and the self-designed bioreactors for experiment in vitro are outlined. An improved understanding of biomechanically driven cartilage tissue engineering and the underlying mechanisms is expected to lead to efficient articular cartilage repair for cartilage degeneration and disease.

Focal adhesion kinase (FAK): its structure, characteristics, and signaling in skeletal system

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase and distributes important regulatory functions in skeletal system. Mesenchymal stem cell (MSC) possesses significant migration and differentiation capacity, is an important source of distinctive bone cells production and a prominent bone development pathway. MSC has a wide range of applications in tissue bioengineering and regenerative medicine, and is frequently employed for hematopoietic support, immunological regulation, and defect repair, although current research is insufficient. FAK has been identified to cross-link with many other keys signaling pathways in bone biology and is considered as a fundamental "crossroad" on the signal transduction pathway and a "node" in the signal network to mediate MSC lineage development in skeletal system. In this review, we summarized the structure, characteristics, cellular signaling, and the interactions of FAK with other signaling pathways in the skeletal system. The discovery of FAK and its mediated molecules will lead to a new knowledge of bone development and bone construction as well as considerable potential for therapeutic use in the treatment of bone-related disorders such as osteoporosis, osteoarthritis, and osteosarcoma.

Obesity, Metabolic Syndrome, and Osteoarthritis-An Updated Review

PURPOSE OF REVIEW

Metabolic syndrome (MetS), also called the 'deadly quartet' comprising obesity, diabetes, dyslipidemia, and hypertension, has been ascertained to have a causal role in the pathogenesis of osteoarthritis (OA). This review is aimed at discussing the current knowledge on the contribution of metabolic syndrome and its various components to OA pathogenesis and progression.

RECENT FINDINGS

Lately, an increased association identified between the various components of metabolic syndrome (obesity, diabetes, dyslipidemia, and hypertension) with OA has led to the identification of the 'metabolic phenotype' of OA. These metabolic perturbations alongside low-grade systemic inflammation have been identified to inflict detrimental effects upon multiple tissues of the joint including cartilage, bone, and synovium leading to complete joint failure in OA. Recent epidemiological and clinical findings affirm that adipokines significantly contribute to inflammation, tissue degradation, and OA pathogenesis mediated through multiple signaling pathways. OA is no longer perceived as just a 'wear and tear' disease and the involvement of the metabolic components in OA pathogenesis adds up to the complexity of the disease. Given the global surge in obesity and its allied metabolic perturbations, this review aims to throw light on the current knowledge on the pathophysiology of MetS-associated OA and the need to address MetS in the context of metabolic OA management. Better regulation of the constituent factors of MetS could be profitable in preventing MetS-associated OA. The identification of key roles for several metabolic regulators in OA pathogenesis has also opened up newer avenues in the recognition and development of novel therapeutic agents.

Stiffened fibre-like microenvironment based on patterned equidistant micropillars directs chondrocyte hypertrophy

Articular cartilage, composed of collagen type II as a major extracellular matrix and chondrocyte as a unique cell type, is a specialized connective tissue without blood vessels, lymphatic vessels and nerves. This distinctive characteristic of articular cartilage determines its very limited ability to repair when damaged. It is well known that physical microenvironmental signals regulate many cell behaviors such as cell morphology, adhesion, proliferation and cell communication even determine chondrocyte fate. Interestingly, with increasing age or progression of joint diseases such as osteoarthritis (OA), the major collagen fibrils in the extracellular matrix of articular cartilage become larger in diameter, leading to stiffening of articular tissue and reducing its resistance to external tension, which in turn aggravates joint damage or progression of joint diseases. Therefore, designing a physical microenvironment closer to the real tissue and thus obtaining data closer to the real cellular behaviour, and then revealing the biological mechanisms of chondrocytes in pathological states is of crucial importance for the treatment of OA disease. Here we fabricated micropillar substrates with the same topology but different stiffnesses to mimic the matrix stiffening that occurs in the transition from normal to diseased cartilage. It was first found that chondrocytes responded to stiffened micropillar substrates by showing a larger cell spreading area, a stronger enhancement of cytoskeleton rearrangement and more stability of focal adhesion plaques. The activation of Erk/MAPK signalling in chondrocytes was detected in response to the stiffened micropillar substrate. Interestingly, a larger nuclear spreading area of chondrocytes at the interface layer between the cells and top surfaces of micropillars was observed in response to the stiffened micropillar substrate. Finally, it was found that the stiffened micropillar substrate promoted chondrocyte hypertrophy. Taken together, these results revealed the cell responses of chondrocytes in terms of cell morphology, cytoskeleton, focal adhesion, nuclei and cell hypertrophy, and may be beneficial for understanding the cellular functional changes affected by the matrix stiffening that occurs during the transition from a normal state to a state of osteoarthritis.

Integrin αVβ3 Signaling in the Progression of Osteoarthritis Induced by Excessive Mechanical Stress

Osteoarthritis (OA) is believed to be linked with cartilage degeneration, subchondral bone sclerosis, and synovial inflammation that lead to joint failure, and yet treatment that can effectively reverse the pathological process of the disease still not exists. Recent evidence suggests excessive mechanical stress (eMS) as an essential role in the pathogenesis of OA. Increased levels of integrin αVβ3 have been detected in osteoarthritic cartilage and were previously implicated in OA pathogenesis. However, the role of integrin αVβ3 in the process of eMS-induced OA remains unclear. Here, histologic and proteomic analyses of osteoarthritic cartilage in a rat destabilization of the medial meniscus model demonstrated elevated expression of integrin αVβ3 as well as more serious cartilage degeneration in the medial weight-bearing area. Furthermore, results of in vitro study demonstrated that eMS led to a significant increase of integrin αVβ3 expression and phosphorylation of downstream signaling molecules such as FAK and ERK, as well as upregulated expressions of inflammatory and degradative mediators. In addition, we found that inhibition of integrin αVβ3 could alleviate chondrocyte inflammation triggered by eMS both in vivo and in vitro. Our findings suggest a central role for upregulation of integrin αVβ3 signaling in OA pathogenesis and demonstrate that activation of integrin αVβ3 signaling in cartilage contributes to inflammation and joint destruction in eMS-induced OA. Taken together, our data presented here provide a possibility for targeting integrin αVβ3 signaling pathway as a disease-modifying therapy.

Intraflagellar transport protein 88 interacts with polycystin 2 to regulate mechanosensitive hedgehog signaling in mandibular condylar chondrocytes

OBJECTIVE

This study aimed to explore whether intraflagellar transport protein 88 (IFT88) was associated with polycystin 2 during mechanotransduction of mandibular condylar chondrocytes.

METHODS

Rat mandibular condylar chondrocytes isolated from the condylar bone-cartilage junction were subjected to cyclic tensile strain (0.1 Hz, 10% elongation). Overexpression of IFT88 was achieved by lentiviral vector-mediated transfection. Knockdown of IFT88 and polycystin 2 was achieved by small interfering RNA (siRNA). The prevalence and length of cilia were reflected by immunofluorescence staining. The activities of hedgehog signaling were evaluated by western blot analysis. The interaction between polycystin 2 and IFT88 was evaluated by conducting a co-immunoprecipitation (co-IP) assay.

RESULTS

Overexpression of IFT88 increased the length of cilia. Protein levels of polycystin 2, Indian hedgehog (Ihh), Patched 1 (Ptch1), Smoothened (Smo), and Glioma-associated oncogene homolog 1 (Gli1) were elevated in IFT88-overexpressing mandibular condylar chondrocytes under cyclic tensile strain. Knockdown of the protein level of IFT88 reduced the prevalence and length of cilia, and protein levels of polycystin 2, Ihh, Ptch1, Smo, and Gli1. A co-IP assay showed that IFT88 formed a complex with polycystin 2 under cyclic tensile strain. Knockdown of polycystin 2 decreased the protein levels of IFT88, Ihh, Ptch1, Smo, and Gli1 in mandibular condylar chondrocytes following cyclic tensile strain.

CONCLUSION

These findings highlight the vital role of an interaction between IFT88 and polycystin 2 in mechanosensitive hedgehog signaling in mandibular condylar chondrocytes following cyclic tensile strain, which suggest that therapies regulating polycystin 2 may be considered for the disorders of temporomandibular joints.

A novel approach to establishing a temporomandibular joint fibrocartilage cell line

Background/purpose

The temporomandibular joint (TMJ) is a bi-arthrodial joint that is composed of the temporal bone glenoid fossa and the condylar head of the mandible both having fibrocartilaginous articular surfaces. Functional overloading of the TMJ is the main cause of TMJ osteoarthritis (TMJ OA) disease. The aim of this study was to establish immortalized TMJ fibrocartilage cell clones to provide enough cells to adequately investigate the molecular mechanisms studies of TMJ OA.

Materials and methods

We have isolated temporomandibular condyle chondrocytes from adult Sprague Dawley rat. The cells were cultured and immortalized by treating with Y-27632, a well-characterized inhibitor of Rho-Associated Kinase (ROCK). Clones were characterized on the basis of cell morphology and analyses of marker gene expression through 45 passages.

Results

Cells from the condylar fibrocartilage of the TMJ were successfully immortalized by ROCK inhibitor, retaining a consistent cuboidal cell morphology and the expression of several cell markers of polymorphic cell fate. In addition, they retained phenotype features similar to the primary parental TMJ fibrocartilage cells when the cells were challenged with different cytokines and growth factors.

Conclusion

These studies establish a novel immortalized cell line through ROCK inhibitor Y-27632, that retains the polymorphic phenotype of primary cell lines from TMJ fibrocartilage chondrocyte cell through a high number of passages, serving as a valuable preclinical resource for mechanistic in vitro assessment of TMJ health, disease, and regeneration.

Cartilage Tissue Engineering Approaches Need to Assess Fibrocartilage When Hydrogel Constructs Are Mechanically Loaded

Chondrocytes that are impregnated within hydrogel constructs sense applied mechanical force and can respond by expressing collagens, which are deposited into the extracellular matrix (ECM). The intention of most cartilage tissue engineering is to form hyaline cartilage, but if mechanical stimulation pushes the ratio of collagen type I (Col1) to collagen type II (Col2) in the ECM too high, then fibrocartilage can form instead. With a focus on Col1 and Col2 expression, the first part of this article reviews the latest studies on hyaline cartilage regeneration within hydrogel constructs that are subjected to compression forces (one of the major types of the forces within joints) in vitro. Since the mechanical loading conditions involving compression and other forces in joints are difficult to reproduce in vitro, implantation of hydrogel constructs in vivo is also reviewed, again with a focus on Col1 and Col2 production within the newly formed cartilage. Furthermore, mechanotransduction pathways that may be related to the expression of Col1 and Col2 within chondrocytes are reviewed and examined. Also, two recently-emerged, novel approaches of load-shielding and synchrotron radiation (SR)–based imaging techniques are discussed and highlighted for future applications to the regeneration of hyaline cartilage. Going forward, all cartilage tissue engineering experiments should assess thoroughly whether fibrocartilage or hyaline cartilage is formed.

Cellular modulation by the mechanical cues from biomaterials for tissue engineering

Mechanical cues from the extracellular matrix (ECM) microenvironment are known to be significant in modulating the fate of stem cells to guide developmental processes and maintain bodily homeostasis. Tissue engineering has provided a promising approach to the repair or regeneration of damaged tissues. Scaffolds are fundamental in cell-based regenerative therapies. Developing artificial ECM that mimics the mechanical properties of native ECM would greatly help to guide cell functions and thus promote tissue regeneration. In this review, we introduce various mechanical cues provided by the ECM including elasticity, viscoelasticity, topography, and external stimuli, and their effects on cell behaviours. Meanwhile, we discuss the underlying principles and strategies to develop natural or synthetic biomaterials with different mechanical properties for cellular modulation, and explore the mechanism by which the mechanical cues from biomaterials regulate cell function toward tissue regeneration. We also discuss the challenges in multimodal mechanical modulation of cell behaviours and the interplay between mechanical cues and other microenvironmental factors.

Mechanical Loading Disrupts Focal Adhesion Kinase Activation in Mandibular Fibrochondrocytes During Murine Temporomandibular Joint Osteoarthritis

PURPOSE

Mechanical overloading is a key initiating condition for temporomandibular joint (TMJ) osteoarthritis (OA). The integrin-focal adhesion kinase (FAK) signaling axis is implicated in the mechanobiological response of cells through phosphorylation at Tyr397 (pFAK) but poorly defined in TMJ health and disease. We hypothesize that mechanical overloading disrupts TMJ homeostasis through dysregulation of FAK signaling.

MATERIALS AND METHODS

To assess if FAK and pFAK are viable clinical targets for TMJ OA, peri-articular tissues were collected from patients with TMJ OA receiving a total TMJ replacement. To compare clinical samples with preclinical in vivo studies of TMJ OA, the joints of c57/bl6 mice were surgically destabilized and treated with and without inhibitor of pFAK (iFAK). FAK signaling and TMJ OA progression was evaluated and compared using RT-PCR, western blot, immunohistochemistry, and histomorphometry. To evaluate mechanical overloading in vitro, primary murine mandibular fibrochondrocytes were seeded in a 4% agarose-collagen scaffold and loaded in a compression bioreactor with and without iFAK.

RESULTS

FAK/pFAK was mostly absent from the articular cartilage layer in the clinical sample and suppressed on the central condyle and elevated on the lateral and medial condyle in murine TMJ OA. In vitro, compressive loading lowered FAK/pFAK levels and elevated the expression of TGFβ, NG2, and MMP-13. iFAK treatment suppressed MMP13 and Col6 and elevated TGFβ, NG2, and ACAN in a load independent manner. In vivo, iFAK treatment moderately attenuated OA progression and increased collagen maturation.

CONCLUSION

These data illustrate that FAK/pFAK is implicated in the signaled dysfunction of excessive mechanical loading during TMJ OA and that iFAK treatment can moderately attenuate the progression of cartilage degeneration in the mandibular condyle.

High-Frequency Near-Infrared Diode Laser Irradiation Attenuates IL-1β-Induced Expression of Inflammatory Cytokines and Matrix Metalloproteinases in Human Primary Chondrocytes

High-frequency near-infrared diode laser provides a high-peak output, low-heat accumulation, and efficient biostimulation. Although these characteristics are considered suitable for osteoarthritis (OA) treatment, the effect of high-frequency near-infrared diode laser irradiation in in vitro or in vivo OA models has not yet been reported. Therefore, we aimed to assess the biological effects of high-frequency near-infrared diode laser irradiation on IL-1β-induced chondrocyte inflammation in an in vitro OA model. Normal Human Articular Chondrocyte-Knee (NHAC-Kn) cells were stimulated with human recombinant IL-1β and irradiated with a high-frequency near-infrared diode laser (910 nm, 4 or 8 J/cm²). The mRNA and protein expression of relevant inflammation- and cartilage destruction-related proteins was analyzed. Interleukin (IL) -1β treatment significantly increased the mRNA levels of IL-1β, IL-6, tumor necrosis factor (TNF) -α, matrix metalloproteinases (MMP) -1, MMP-3, and MMP-13. High-frequency near-infrared diode laser irradiation significantly reduced the IL-1β-induced expression of IL-1β, IL-6, TNF-α, MMP-1, and MMP-3. Similarly, high-frequency near-infrared diode laser irradiation decreased the IL-1β-induced increase in protein expression and secreted levels of MMP-1 and MMP-3. These results highlight the therapeutic potential of high-frequency near-infrared diode laser irradiation in OA.

Protective effects of cilengitide on inflammation in chondrocytes under excessive mechanical stress

Chondrocytes constantly receive external stimuli, which regulates remodeling. An optimal level of mechanical stress is essential for maintaining chondrocyte homeostasis, however, excessive mechanical stress induces inflammatory cytokines and protease, such as matrix metalloproteinases (MMPs). Therefore, excessive mechanical stress is considered to be one of the main causes to cartilage destruction leading to osteoarthritis (OA). Integrins are well-known as cell adhesion molecules and act as receptors for extracellular matrix (ECM), and are believed to control intracellular signaling pathways both physically and chemically as a mechanoreceptor. However, few studies have focused on the roles and functions of integrins in inflammation caused by excessive mechanical stress. In this study, we examined the relationship between integrins (αVβ3 and αVβ5) and the expression of inflammatory factors under mechanical loading in chondrocytes by using an integrin receptor antagonist (cilengitide). Cilengitide suppressed the gene expression of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), matrix metalloproteinase-3 (MMP-3), and MMP-13 induced by excessive mechanical stress. In addition, the protein expression of IL1-β and MMP-13 was also inhibited by the addition of cilengitide. Next, we investigated the involvement of intracellular signaling pathways in stress-induced integrin signaling in chondrocytes by using western blotting. The levels of p-FAK, p-ERK, p-JNK, and p-p38 were enhanced by excessive mechanical stress and the enhancement was suppressed by treatment with cilengitide. In conclusion, this study revealed that excessive mechanical stress may activate integrins αVβ3 and αVβ5 on the surface of chondrocytes and thereby induce an inflammatory reaction by upregulating the expression of IL-1β, TNF-α, MMP-3, and MMP-13 through phosphorylation of FAK and MAPKs.

Combination of estrogen deficiency and excessive mechanical stress aggravates temporomandibular joint osteoarthritis in vivo

OBJECTIVE

It has been suggested that degenerative conditions of the temporomandibular joint (TMJ), such as osteoarthritis (OA) and progressive condylar resorption, are caused by multiple etiological factors, such as hormonal imbalance and excessive mechanical stress. However, it is unclear whether these factors interrelate in the degenerative process of the condyle. The aim of this study was to observe the effects of combined hormonal imbalance and excessive mechanical stress on the condyle using a mouse model.

MATERIALS AND METHODS

Ovariectomy (OVX) was performed in 8-week-old female mice. Three weeks after OVX, a build-up resin was bonded to the right maxillary molars to create imbalanced occlusion (increased occlusal vertical dimension, iOVD). Mice were divided into four groups: control, OVX, iOVD, and OVX + iOVD.

RESULTS

Histomorphometric analysis showed the lowest cartilage thickness and the highest TMJ-OA score in the OVX + iOVD group. Bone structural analysis showed significantly lower subchondral bone mass in all experimental groups. Additionally, the OVX + iOVD group showed up-regulated osteoclastic activity and increased apoptosis in the condyle. Gene expression analysis showed significantly elevated expression of pre-inflammatory cytokines in the OVX + iOVD group. These data showed that the OVX + iOVD group exhibited the most severe inflammatory TMJ-OA. Upregulation of ERα and activation of the ERK pathway was observed in the OVX + iOVD group.

CONCLUSIONS

Additive effects of estrogen deficiency and excessive mechanical stress on the condyle exacerbate TMJ-OA. Furthermore, estrogen deficiency and excessive mechanical stress combined may exacerbate TMJ-OA though activation of the ERK pathway.

Cells under stress: The mechanical environment shapes inflammasome responses to danger signals

Many intracellular signals, such as host danger-associated molecules and bacterial toxins during infection, elicit inflammasome activation. However, the mechanical environment in tissues may also influence the sensitivity of various inflammasomes to activation. The cellular mechanical environment is determined by the extracellular tissue stiffness, or its inverse, tissue compliance. Tissue stiffness is sensed by the intracellular cytoskeleton through a process termed mechanotransduction. Thus, extracellular compliance and the intracellular cytoskeleton may regulate the sensitivity of inflammasome activation. Control of proinflammatory signaling by tissue compliance may contribute to the pathogenesis of diseases such as ventilator-induced lung injury during bacterial pneumonia and tissue fibrosis in inflammatory disorders. The responsible signaling cascades in inflammasome activation pathways and mechanotransduction crosstalk are not yet fully understood. This rather different immunomodulatory perspective will be reviewed and open questions discussed here.

Vascular endothelial growth factor-C promotes human mesenchymal stem cell migration via an ERK-and FAK-dependent mechanism

Vascular endothelial cell growth factor-C (VEGF-C) is a member of the VEGF family and plays a role in various biological activities. VEGF-C enhances proliferation and migration of lymphatic endothelial cells and vascular endothelial cells through VEGF receptor 2 (VEGFR2) and/or receptor 3 (VEGFR3), and thereby induces lymphangiogenesis or angiogenesis. However, it remains unclear whether VEGF-C promotes the migration of mesenchymal stem cells (MSCs). Here, we investigated the effects of VEGF-C on the migration of MSCs and evaluated the underlying molecular mechanisms. VEGF-C treatment significantly induced the migration of MSCs, which is accompanied by the promotion of actin cytoskeletal reorganization and focal adhesion assembly. VEGF-C treatment enhanced the phosphorylation of VEGFR2 and VEGFR3 proteins in MSCs, and pretreatment with VEGFR2 and VEGFR3 kinase inhibitors effectively suppressed the VEGF-C-induced MSC migration. In addition, VEGF-C treatment promoted phosphorylation of ERK and FAK proteins in MSCs, and inhibition of VEGFR2 and VEGFR3 signaling pathways abolished the VEGF-C-induced activation of ERK and FAK proteins. Furthermore, treatment with ERK and FAK inhibitors suppressed VEGF-C-induced actin cytoskeletal reorganization and focal adhesion assembly, and then significantly inhibited MSCs migration. These results suggest that VEGF-C-induced MSC migration is mediated via VEGFR2 and VEGFR3, and follows the activation of the ERK and FAK signaling pathway. Thus, VEGF-C may be valuable in tissue regeneration and repair in MSC-based therapy.