Effect of hypoxia and interleukin-1beta on expression of tenascin-C in temporomandibular joint

Effects of hypoxia on bronchial and alveolar epithelial cells linked to pathogenesis in chronic lung disorders

Introduction: Chronic lung disorders involve pathological alterations in the lung tissue with hypoxia as a consequence. Hypoxia may influence the release of inflammatory mediators and growth factors including vascular endothelial growth factor (VEGF) and prostaglandin (PG)E2. The aim of this work was to investigate how hypoxia affects human lung epithelial cells in combination with profibrotic stimuli and its correlation to pathogenesis.

Methods: Human bronchial (BEAS-2B) and alveolar (hAELVi) epithelial cells were exposed to either hypoxia (1% O2) or normoxia (21% O2) during 24 h, with or without transforming growth factor (TGF)-β1. mRNA expression of genes and proteins related to disease pathology were analysed with qPCR, ELISA or immunocytochemistry. Alterations in cell viability and metabolic activity were determined.

Results: In BEAS-2B and hAELVi, hypoxia significantly dowregulated genes related to fibrosis, mitochondrial stress, oxidative stress, apoptosis and inflammation whereas VEGF receptor 2 increased. Hypoxia increased the expression of Tenascin-C, whereas both hypoxia and TGF-β1 stimuli increased the release of VEGF, IL-6, IL-8 and MCP-1 in BEAS-2B. In hAELVi, hypoxia reduced the release of fibroblast growth factor, epidermal growth factor, PGE2, IL-6 and IL-8, whereas TGF-β1 stimulus significantly increased the release of PGE2 and IL-6. TGF-β1 stimulated BEAS-2B cells showed a decreased release of VEGF-A and IL-8, while TGF-β1 stimulated hAELVi cells showed a decreased release of PGE2 and IL-8 during hypoxia compared to normoxia. Metabolic activity was significantly increased by hypoxia in both epithelial cell types.

Discussion: In conclusion, our data indicate that bronchial and alveolar epithelial cells respond differently to hypoxia and profibrotic stimuli. The bronchial epithelium appears more responsive to changes in oxygen levels and remodelling processes compared to the alveoli, suggesting that hypoxia may be a driver of pathogenesis in chronic lung disorders.

IL-33/ST2 axis promotes glioblastoma cell invasion by accumulating tenascin-C

Tenascin-C (TNC), a very large multimeric glycoprotein, is overexpressed in human glioblastomas, leading to a highly motile and invasive phenotype of glioma cells. However, the regulation of TNC expression in glioma has remained unclear until now. Our data suggest that interleukin-33 (IL-33) may promote the accumulation of TNC protein by autocrine or paracrine modes of action in glioma. In the present study, the expression levels of TNC, IL-33, and ST2 were measured in glioma tissue specimens, and the impact of altered IL-33 expression on TNC was investigated in vitro and in vivo. In contrast with control treatment, IL-33 treatment increased TNC expression, and knockdown of IL-33 attenuated TNC expression in glioma cells. Furthermore, IL-33 induced the activation of nuclear factor κB (NF-κB) and increased the expression of TNC in U251 cells. In addition, blockage of the IL-33-ST2-NFκB pathway resulted in downregulation of TNC production. IL-33 promoted glioma cell invasion by stimulating the secretion of TNC. Similarly, knockdown of TNC inhibited the invasiveness of glioma cells. These findings provide a novel perspective on the role of the IL-33/NF-κB/TNC signalling pathway in supporting cancer progression. Thus, targeting the IL-33/NF-κB/TNC signalling pathway may be a useful therapeutic approach in glioma.

Effect of Sustained Joint Loading on TMJ Disc Nutrient Environment

The temporomandibular joint (TMJ) disc nutrient environment profoundly affects cell energy metabolism, proliferation, and biosynthesis. Due to technical challenges of in vivo measurements, the human TMJ disc extracellular nutrient environment under load, which depends on metabolic rates, solute diffusion, and disc morphometry, remains unknown. Therefore, the study objective was to predict the TMJ disc nutrient environment under loading conditions using combined experimental and computational modeling approaches. Specifically, glucose consumption and lactate production rates of porcine TMJ discs were measured under varying tissue culture conditions (n = 40 discs), and mechanical strain-dependent glucose and lactate diffusivities were measured using a custom diffusion chamber (n = 6 discs). TMJ anatomy and loading area were obtained from magnetic resonance imaging of healthy human volunteers (n = 11, male, 30 ± 9 y). Using experimentally determined nutrient metabolic rates, solute diffusivities, TMJ anatomy, and loading areas, subject-specific finite element (FE) models were developed to predict the 3-dimensional nutrient profiles in unloaded and loaded TMJ discs (unloaded, 0% strain, 20% strain). From the FE models, glucose, lactate, and oxygen concentration ranges for unloaded healthy human TMJ discs were 0.6 to 4.0 mM, 0.9 to 5.0 mM, and 0% to 6%, respectively, with steep gradients in the anterior and posterior bands. Sustained mechanical loading significantly reduced nutrient levels (P < 0.001), with a critical zone in which cells may die representing approximately 13.5% of the total disc volume. In conclusion, this study experimentally determined TMJ disc metabolic rates, solute diffusivities, and disc morphometry, and through subject-specific FE modeling, revealed critical interactions between mechanical loading and nutrient supply and metabolism for the in vivo human TMJ disc. The results suggest that TMJ disc homeostasis may be vulnerable to pathological loading (e.g., clenching, bruxism), which impedes nutrient supply. Given difficulties associated with direct in vivo measurements, this study provides a new approach to systematically investigate homeostatic and degenerative mechanisms associated with the TMJ disc.

The effects of oxygen level and glucose concentration on the metabolism of porcine TMJ disc cells

OBJECTIVE

To determine the combined effect of oxygen level and glucose concentration on cell viability, ATP production, and matrix synthesis of temporomandibular joint (TMJ) disc cells.

DESIGN

TMJ disc cells were isolated from pigs aged 6-8 months and cultured in a monolayer. Cell cultures were preconditioned for 48 h with 0, 1.5, 5, or 25 mM glucose DMEM under 1%, 5%, 10%, or 21% O2 level, respectively. The cell viability was measured using the WST-1 assay. ATP production was determined using the Luciferin-Luciferase assay. Collagen and proteoglycan synthesis were determined by measuring the incorporation of [2, 3-(3)H] proline and [(35)S] sulfate into the cells, respectively.

RESULTS

TMJ disc cell viability significantly decreased (P < 0.0001) without glucose. With glucose present, decreased oxygen levels significantly increased viability (P < 0.0001), while a decrease in glucose concentration significantly decreased viability (P < 0.0001). With glucose present, decreasing oxygen levels significantly reduced ATP production (P < 0.0001) and matrix synthesis (P < 0.0001). A decreased glucose concentration significantly decreased collagen synthesis (P < 0.0001). The interaction between glucose and oxygen was significant in regards to cell viability (P < 0.0001), ATP production (P = 0.00015), and collagen (P = 0.0002) and proteoglycan synthesis (P < 0.0001).

CONCLUSIONS

Although both glucose and oxygen are important, glucose is the limiting nutrient for TMJ disc cell survival. At low oxygen levels, the production of ATP, collagen, and proteoglycan are severely inhibited. These results suggest that steeper nutrient gradients may exist in the TMJ disc and it may be vulnerable to pathological events that impede nutrient supply.

Inhibition of fibrous adhesion formation in the temporomandibular joint of tenascin-C knockout mice

Tenascin-C (TNC) is a large hexameric extracellular matrix glycoprotein that is expressed in developing organs and tumors. It has been reported that TNC is expressed in inflamed synovial membranes and deformed discs of temporomandibular joint (TMJ) disorder. However, the role of TNC in TMJ is not fully known. In this study, the role of TNC in fibrous adhesion formation of TMJ was examined using TNC knockout (TNCKO) mice. Hypermobility was produced by excessive mouth opening method on the TMJ of both wild-type (WT) and TNCKO mice. TMJ wound healing was compared histologically, and the expression of TNC, fibronectin (FN) and α-smooth muscle actin (α-SMA) in the wounded TMJ was examined by immunohistochemical and immunoblot analyses. Based on histologic analysis, fibrous adhesions were observed in the TMJ of both TNCKO and wild-type (WT) mice after excessive mouth opening. However, fibrous adhesion formation in TNCKO mice occurred later than in WT mice. TNC was expressed in the wounded TMJ disc and mandibular fossa. Although FN and α-SMA expression in the TMJ of TNCKO and WT mice was up-regulated after excessive mouth opening, FN and α-SMA protein levels were higher in WT mice at the same time points. In the wounded TMJ, TNC appears to enhance the expression of FN and α-SMA, and a lack of TNC may reduce fibrous adhesion formation in the TMJ. TNC plays an important role in TMJ wound healing, especially for wounds generated by mechanical stress.

Effect of mechanical strain on solute diffusion in human TMJ discs: an electrical conductivity study

This study investigated the effect of mechanical strain on solute diffusion in human TMJ discs (mean cadaver age 77.8) using the electrical conductivity method. The electrical conductivity, as well as small ion diffusivity, of male and female TMJ discs was determined under three compressive strains. In the male group, the average disc electrical conductivity (mean ± SD) at 0% strain was 5.14 ± 0.97 mS/cm, decreased to 4.50 ± 0.91 mS/cm (-12.3%) at 10% strain, and 3.93 ± 0.81 mS/cm (-23.5%) at 20% compressive strain. Correspondingly, the average disc relative ion diffusivity at 0% strain was 0.44 ± 0.08, decreased to 0.40 ± 0.08 (-8.9%) at 10% strain, and 0.36 ± 0.08 (-16.7%) at 20% compressive strain. In the female group, the average disc electrical conductivity at 0% strain was 5.84 ± 0.59 mS/cm, decreased to 5.01 ± 0.50 mS/cm (-14.2%) at 10% strain, and 4.33 ± 0.46 mS/cm (-25.8%) at 20% compressive strain. Correspondingly, the average disc relative ion diffusivity at 0% strain was 0.49 ± 0.05, decreased to 0.43 ± 0.04 (-11.3%) at 10% strain, and 0.39 ± 0.04 (-19.9%) at 20% compressive strain. The results indicated that mechanical strain significantly impeded solute diffusion through the disc. This mechanical strain effect was larger in the female than in the male human TMJ disc. This study may provide new insights into TMJ pathophysiology.

Relationship between anisotropic diffusion properties and tissue morphology in porcine TMJ disc

OBJECTIVE

To investigate the relationship between anisotropic solute diffusion properties and tissue morphology in porcine temporomandibular joint (TMJ) discs.

DESIGN

TMJ discs from eleven pigs aged 6-8 months were divided into five regions: anterior, intermediate, posterior, lateral, and medial. The transport properties and tissue morphology were investigated in three orthogonal orientations: anteroposterior (AP), mediolateral (ML), and superoinferior (SI). The anisotropic diffusivity of fluorescein (332 Da) in the right discs was determined by the fluorescence recovery after photobleaching (FRAP) protocols. The tissue morphology in the left discs was quantified by scanning electron microscopy.

RESULTS

The diffusivities of fluorescein in the TMJ disc were significantly anisotropic, except for the anterior region. In the medial, intermediate, and lateral regions, the diffusion along the fiber orientation (i.e., AP direction) was significantly faster than the diffusion in ML and SI directions. In the posterior region, the diffusion along the fiber orientation (i.e., ML direction) was significantly faster than the diffusion in AP and SI directions. The diffusion in the anterior region was mostly isotropic with the lowest degree of diffusion anisotropy, as well as collagen fiber alignment, likely due to the multi-directional fiber arrangement. The anterior region had the highest mean diffusivity [65.6 (49.3-81.8) μm(2)/s] in the disc, likely due to its high water content. The overall average diffusivity of fluorescein across the TMJ disc was 57.0 (43.0-71.0) μm(2)/s.

CONCLUSIONS

The solute diffusion in porcine TMJ discs was strongly anisotropic and inhomogeneous, which associated with tissue structure (i.e., collagen fiber alignment) and composition (e.g., water content).

Hypoxia Affects the Structure of Breast Cancer Cell-Derived Matrix to Support Angiogenic Responses of Endothelial Cells

Hypoxia, a common feature of the tumor environment and participant in tumor progression, is known to alter gene and protein expression of several Extracellular Matrix (ECM) proteins, many of which have roles in angiogenesis. Previously, we reported that ECM deposited from co-cultures of Neonatal Fibroblasts (NuFF) with breast cancer cells, supported 3-dimensional vascular morphogenesis. Here, we sought to characterize the hypoxic ECM and to identify whether the deposited ECM induce angiogenic responses in Endothelial Cells (ECs). NuFF and MDA-MB-231 breast cancer cells were co-cultured, subjected to alternating cycles of 24 hours of 1% (hypoxia) and 21% (atmospheric) oxygen and de-cellularized for analyses of deposited ECM. We report differences in mRNA expression profiles of matrix proteins and crosslinking enzymes relevant to angiogenesis in hypoxia-exposed co-cultures. Interestingly, overt differences in the expression of ECM proteins were not detected in the de-cellularized ECM; however, up-regulation of the cell-binding fragment of fibronecin was observed in the conditioned media of hypoxic co-cultures. Ultrastructure analyses of the de-cellularized ECM revealed differences in fiber morphology with hypoxic fibers more compact and aligned, occupying a greater percent area and having larger diameter fibers than atmospheric ECM. Examining the effect of hypoxic ECM on angiogenic responses of ECs, morphological differences in Capillary-Like Structures (CLS) formed atop de-cellularized hypoxic and atmospheric ECM were not evident. Interestingly, we found that hypoxic ECM regulated the expression of angiogenic factors and matrix metalloproteinases in CLS. Overall, we report that in vitro, hypoxia does not alter the composition of the ECM deposited by co-cultures of NuFF/MDA-MB-231, but rather alters fiber morphology, and induces vascular expression of angiogenic growth factors and metalloproteinases. Taken together, these results have important implications for understanding how the hypoxic matrix may regulate angiogenesis in tumors.

Effect of mechanical loading on electrical conductivity in porcine TMJ discs

The objective of this study was to examine the impact of mechanical loading on solute transport in porcine temporomandibular joint (TMJ) discs using the electrical conductivity method. The electrical conductivity, as well as ion diffusivity, of TMJ discs was determined under confined compression with 3 strains in 5 disc regions. The average electrical conductivity over the 5 regions (mean ± SD) at 0% strain was 3.10 ± 0.68 mS/cm, decreased to 2.76 ± 0.58 mS/cm (-11.0%) at 10% strain, and 2.38 ± 0.55 mS/cm (-22.2%) at 20% compressive strain. Correspondingly, the average relative ion diffusivity (mean ± SD) at 0% strain was 0.273 ± 0.055, decreased to 0.253 ± 0.048 (-7.3%) at 10% strain, and 0.231 ± 0.048 (-15.4%) at 20% compressive strain. These results indicated that compressive strain impeded solute transport in the TMJ disc. Furthermore, our results showed that the transport properties of TMJ discs were region-dependent. The electrical conductivity and ion diffusivity in the anterior region were significantly higher than in the posterior region. This regional difference is likely due to the significant differences of tissue hydration between these 2 regions. This study provides important insight into the electrical and solute transport behaviors in TMJ discs under mechanical loading and aids in the understanding of TMJ pathophysiology related to tissue nutrition.

Regional cell density distribution and oxygen consumption rates in porcine TMJ discs: an explant study

OBJECTIVE

To determine the regional cell density distribution and basal oxygen consumption rates (based on tissue volume and cell number) of temporomandibular joint (TMJ) discs and further examine the impact of oxygen tension on these rates.

DESIGN

TMJ discs from pigs aged 6-8 months were divided into five regions: anterior, intermediate, posterior, lateral and medial. The cell density was determined using confocal laser scanning microscopy. The change in oxygen tension was recorded while TMJ disc explants were cultured in sealed metabolism chambers. The volume based oxygen consumption rate of explants was determined by theoretical curve-fitting of the recorded oxygen tension data with the Michaelis-Menten equation. The rate on a per-cell basis was calculated based on the cell density measurements and volume based rate measured in another group of discs.

RESULTS

The overall cell density [mean, 95% confidence interval (CI)] was 51.3 (21.3-81.3) × 10(6) cells/mL wet tissue. Along the anteroposterior axis, the anterior band had 25.5% higher cell density than the intermediate zone (P<0.02) and 29.1% higher than the posterior band (P<0.008). Along the mediolateral axes, the medial region had 26.2% higher cell density than the intermediate zone (P<0.04) and 25.4% higher than the lateral region (P<0.045). The overall volume and cell based maximum oxygen consumption rates were 1.44 (0.44-2.44) μmol/mL wet tissue/h and 28.7 (12.2-45.2)nmol/10(6)cells/h, respectively. The central regions (intermediate, lateral, and medial) had significantly higher volume based (P<0.02) and cell based (P<0.005) oxygen consumption rates than the anterior and posterior bands. At high oxygen tension, the oxygen consumption rate remained constant, but dropped as oxygen tension fell below 5%.

CONCLUSIONS

The TMJ disc had higher cell density and oxygen consumption rates than articular cartilage reported in the literature. These results suggest that a steeper oxygen gradient may exist in the TMJ disc and may be vulnerable to pathological events that impede nutrient supply.

Expression of Ten-m/Odz3 in the fibrous layer of mandibular condylar cartilage during postnatal growth in mice

It has been speculated that the mandibular condyle develops via the differentiation of the fibroblast-like cells covering the condyle into chondrocytes; however, the developmental mechanisms behind this process have not been revealed. We used laser-capture microdissection and cDNA microarray analysis to elucidate the genes that are highly expressed in these fibroblast-like cells. Among these genes, the transcription of Ten-m/Odz3 was significantly increased in the fibroblast-like cells compared with other cartilage tissues. For the first time, we describe the temporal and spatial expression of Ten-m/Odz3 mRNA in relation to the expression of type I, II, and X collagen mRNA, as determined by in-situ hybridization in mouse mandibular condylar cartilage and mouse femoral cartilage during the early stages of development. Ten-m/Odz3 was expressed in the fibrous layer and the proliferating and mature chondrocyte layers, which expressed type I and II collagen, respectively, but was not detected in the hypertrophic chondrocyte layer. Furthermore, we evaluated the in-vitro expression of Ten-m/Odz3 using ATDC5 cells, a mouse chondrogenic cell line. Ten-m/Odz3 was expressed during the early stage of the differentiation of mesenchymal cells into chondrocytes. These findings suggest that Ten-m/Odz3 is involved in the differentiation of chondrocytes and that it acts as a regulatory factor in the early stages of the development of mandibular condylar cartilage.