Effects of hypoxia on anabolic and catabolic gene expression and DNA methylation in OA chondrocytes

Use of polyglycolic acid-hyaluronic acid/β-tricalcium phosphate scaffold with or without mesenchymal stem cells found ineffective in treating osteochondral lesions in rabbit knees

OBJECTIVE

In this experimental animal study, a novel bilayered scaffold used in the treatment of osteochondral defects in rabbit knees was evaluated. This novel scaffold's upper (cartilage) layer consists of polyglycolic acid and hyaluronic acid, and the lower (bone) layer consists of β-tricalcium phosphate. The purpose of this study was to evaluate the efficacy of this novel scaffold, combined with or without mesenchymal stem cells (MSCs), in the treatment of osteochondral defects in rabbit knees.

METHODS

Osteochondral defects were created in the left femoral trochlea of 30 rabbits. In group A, defects were treated with scaffold combined with MSCs; in group B, defects were treated with cell-free scaffolds; and group C was a control group with defects left untreated. In the 12th week, animals were sacrificed for macroscopic evaluation.

RESULTS

The mean International Cartilage Repair Society (ICRS) macroscopic scores were 4.95 for group A, 6.16 for group B, and 8.25 for group C. The mean Oswestry Arthroscopic Scores (OAS) were 1.65 for group A, 3.39 for group B, and 6.05 for group C. The macroscopic scores were significantly higher in group C than group A for ICRS scores and group A and group B for OAS (P < .001, P < .000, P < .022).

CONCLUSION

In essence, our findings indicate that the newly developed osteochondral scaffold, when tested in a rabbit model, is not as effective as expected in repairing full-thickness osteochondral defects, with or without the supplementation of MSCs. Further investigation is required to enhance the effectiveness of this novel combination.

A Novel Hypoxia Related Marker in Blood Link to Aid Diagnosis and Therapy in Osteoarthritis

Osteoarthritis (OA) is a common chronic degenerative arthritis. Its treatment options are very limited. At present, hypoxia is a prominent factor in OA. This study aimed to re-explore the mechanism between hypoxia and OA, which provides new insights into the diagnosis and therapy of OA. We acquired the OA-related expression profiles of GSE48556, GSE55235, and GSE55457 for our analysis. Using gene set variation analysis (GSVA), we found significant differences in hypoxia. These differences result from multiple pathways, such as the p53 signaling pathway, cell senescence, the NF-kappa B signaling pathway, Ubiquitin-mediated proteolysis, and apoptosis. Meanwhile, the single-sample gene set enrichment analysis (ssGSEA) showed that hypoxia was significantly associated with the level of immune cell infiltration in the immune microenvironment. Thus, we believe that hypoxia is useful for the diagnosis and treatment of OA. We successfully constructed a novel hypoxia-related index (HRI) based on seven hypoxia-related genes (ADM, CDKN3, ENO1, NDRG1, PGAM1, SLC2A1, VEGFA) by least absolute shrinkage and binary logistic regression of the generalized linear regression. HRI showed potential for improving OA diagnosis through receiver operation characteristic (ROC) analysis (AUC training cohort = 0.919, AUC testing cohort = 0.985). Moreover, we found that celastrol, droxinostat, torin-2, and narciclasine may be potential therapeutic compounds for OA based on the Connectivity Map (CMap). In conclusion, hypoxia is involved in the development and progression of OA. HRI can improve diagnosis and show great potential in clinical application. Celastrol, droxinostat, torin-2, and narciclasine may be potential compounds for the treatment of OA patients.

Hypoxia Affects HIF-1/LDH-A Signaling Pathway by Methylation Modification and Transcriptional Regulation in Japanese Flounder (Paralichthys olivaceus)

Simple Summary

With global climate change and increased aquaculture production, fishes in natural waters or aquaculture systems are easily subjected to hypoxic stress. However, our understanding about their responsive mechanisms to hypoxia is still limited. Japanese flounder (Paralichthys olivaceus) is a widely cultivated marine economical flatfish, whose hypoxic responsive mechanisms are not fully researched. In this study, responses to hypoxia were investigated at blood physiological, biochemical, hormonal, and molecular levels. Responsive mechanisms of the HIF-1/LDH-A signaling pathway in epigenetic modification and transcriptional regulation were also researched. These results are important for enriching the theory of environmental responsive mechanisms and guiding aquaculture.

Abstract

Japanese flounder (Paralichthys olivaceus) responsive mechanisms to hypoxia are still not fully understood. Therefore, we performed an acute hypoxic treatment (dissolved oxygen at 2.07 ± 0.08 mg/L) on Japanese flounder. It was confirmed that the hypoxic stress affected the physiological phenotype through changes in blood physiology (RBC, HGB, WBC), biochemistry (LDH, ALP, ALT, GLU, TC, TG, ALB), and hormone (cortisol) indicators. Hypoxia inducible factor-1 (HIF-1), an essential oxygen homeostasis mediator in organisms consisting of an inducible HIF-1α and a constitutive HIF-1β, and its target gene LDH-A were deeply studied. Results showed that HIF-1α and LDH-A genes were co-expressed and significantly affected by hypoxic stress. The dual-luciferase reporter assay confirmed that transcription factor HIF-1 transcriptionally regulated the LDH-A gene, and its transcription binding sequence was GGACGTGA located at −2343~−2336. The DNA methylation status of HIF-1α and LDH-A genes were detected to understand the mechanism of environmental stress on genes. It was found that hypoxia affected the HIF-1α gene and LDH-A gene methylation levels. The study uncovered HIF-1/LDH-A signaling pathway responsive mechanisms of Japanese flounder to hypoxia in epigenetic modification and transcriptional regulation. Our study is significant to further the understanding of environmental responsive mechanisms as well as providing a reference for aquaculture.

Observation of Solute Transport between Articular Cartilage and Subchondral Bone in Live Mice

OBJECTIVE

To establish a method for investigating the permeability of calcified cartilage zone (CCZ) and to observe solute transport between articular cartilage (AC) and subchondral bone (SB) through intact CCZ in vivo.

DESIGN

We developed a novel fixing device combined with un-decalcified fluorescence observation method to address the permeability of CCZ in live mice. Twenty-four Balb/c female mice aged 1 to 8 months were used to observe the development of CCZ. Eighty-four Balb/c female mice (aged 1 or 6 months) with mature or immature CCZ of distal femur were used to investigate the permeability of intact CCZ in vivo. Diffusivity of rhodamine B (476 Da) and tetramethyl-rhodamine isothicyanate-dextran (TRITC-Dextran, 20 kDa) was tested from AC to SB in 0 minutes, 1 minute, 15 minutes, 30 minutes, 1 hour, and 2 hours. None diffused knee joints (0 minutes) served as blank control, while in vitro immersion of distal femurs in rhodamine B or TRITC-Dextran for 72 hours served as positive control.

RESULTS

CCZ was well developed in 6-month mice. Both tracers penetrated immature CCZ down to SB in less than 1 hour in live mice, while the diffusion of both tracers decreased rapidly at tidemark in all testing time points.

CONCLUSION

Current study provided direct evidence of blocking effect of CCZ in solute transportation during short diffusion period in live animal, indicating the important role of CCZ in joint development and microenvironment maintenance.

Scaffold With Natural Calcified Cartilage Zone for Osteochondral Defect Repair in Minipigs

BACKGROUND

Long-term outcomes of current clinical interventions for osteochondral defect are less than satisfactory. One possible reason is an ignorance of the interface structure between cartilage and subchondral bone, the calcified cartilage zone (CCZ). However, the importance of natural CCZ in osteochondral defects has not been directly described.

PURPOSE

To explore the feasibility of fabricating trilayer scaffold containing natural CCZ for osteochondral defects and the role of CCZ in the repair process.

STUDY DESIGN

Controlled laboratory study.

METHODS

The scaffold was prepared by cross-linking lyophilized type II collagen sponge and acellular normal pig subchondral bone with or without natural CCZ. Autologous bone marrow stem cells (BMSCs) of minipig were mixed with type II collagen gel and injected into the cartilage layer of the scaffold before operation. Thirty minipigs were randomly divided into CCZ (n = 10), non-CCZ (n = 10), and blank control (n = 10) groups. An 8 mm-diameter full-thickness osteochondral defect was created on the trochlear surface, and scaffold containing BMSCs was transplanted into the defect according to grouping requirements. At 12 and 24 weeks postoperatively, specimens were assessed by macroscopic observation, magnetic resonance imaging examination, and histological observations (hematoxylin and eosin, Safranin O-fast green, type II collagen immunohistochemical, and Sirius red staining). Semiquantitative cartilage repair scoring was conducted using the MOCART (Magnetic Resonance Observation of Cartilage Repair Tissue) system and the O'Driscoll repaired cartilage value system.

RESULTS

The defects in the blank control and non-CCZ groups were filled with fibrous tissue, while the cartilage layer of the CCZ group was mainly repaired by hyaline cartilage at 24 weeks postoperatively. The superior repair outcome of the CCZ group was confirmed by MOCART and O'Driscoll score.

CONCLUSION

The trilayer scaffold containing natural CCZ obtained the best repair effect compared with the non-CCZ scaffold and the blank control, indicating the importance of the CCZ in osteochondral tissue engineering.

CLINICAL RELEVANCE

This study demonstrates the necessity to reconstruct CCZ in clinical osteochondral defect repair and provides a possible strategy for osteochondral tissue engineering.

Relationship between osteoporosis and osteoarthritis based on DNA methylation

The aim of this study was to investigate the relationship between osteoporosis and osteoarthritis by analyzing the DNA methylation in osteoporosis and osteoarthritis. The cancellous bone specimens were collected from a total of 12 hospitalized patients and divided into the osteoporosis group (OA), the osteoarthritis group (OP), the osteoporosis combined with osteoarthritis group (OA & OP), and the normal control group (N). The cancellous bone specimens of each group were detected and the differences in gene expression profiles by the MeDIP-chip technique were compared. Compared with Group OA & OP, the methylation levels in Group OA and Group OP were statistically higher, P < 0.05. In the microarray analysis, a total of 1,222 sites occurred hypermethylation. The analysis targeting the differentially expressed genes between Group OA & OP and Group N revealed that group OA and group OP had 4 common genes: PPIL3, NIF3L1, SMTN, and CALHM2. The level of genomic methylation is lower in the patients with osteoporosis and/or osteoarthritis. The common difference between osteoarthritis and osteoporosis is reflected in some specific promoters, which may participate in the processes of diseases through different pathways.

Epigenetic regulation of metalloproteinases and their inhibitors in rotator cuff tears

Rotator cuff tear is a common orthopedic condition. Metalloproteinases (MMP) and their inhibitors (TIMP) seem to play a role in the development of joint injuries and in the failure of tissue healing. However, the mechanisms of regulation of gene expression in tendons are still unknown. Epigenetic mechanisms, such as DNA methylation and microRNAs regulation, are involved in the dynamic control of gene expression. Here, the mRNA expression and DNA methylation status of MMPs (MMP1, MMP2, MMP3, MMP9, MMP13, and MMP14) and TIMPs (TIMP1-3) and the expression of miR-29 family members in ruptured supraspinatus tendons were compared with non-injured tendons of individuals without this lesion. Additionally, the gene expression and methylation status at the edge of the ruptured tendon were compared with macroscopically non-injured rotator cuff tendon samples from the anterior and posterior regions of patients with tendon tears. Moreover, the possible associations between the molecular alterations and the clinical and histologic characteristics were investigated. Dysregulated expression and DNA methylation of MMP and TIMP genes were found across the rotator cuff tendon samples of patients with supraspinatus tears. These alterations were influenced at least in part by age at surgery, sex, smoking habit, tear size, and duration of symptoms. Alterations in the studied MMP and TIMP genes may contribute to the presence of microcysts, fissures, necrosis, and neovascularization in tendons and may thus be involved in the tendon healing process. In conclusion, MMPs and their inhibitors are regulated by epigenetic modifications and may play a role in rotator cuff tears.

Epigenetics in osteoarthritis: Potential of HDAC inhibitors as therapeutics

Osteoarthritis (OA) is the most common joint disease and the leading cause of chronic disability in middle-aged and older populations worldwide. The development of disease modifying therapy for OA is in its infancy largely because the regulatory mechanisms for the molecular effectors of OA pathogenesis are poorly understood. Recent studies identified epigenetic events as a critical regulator of molecular players involved in the induction and development of OA. Epigenetic mechanisms include DNA methylation, non-coding RNA and histone modifications. The aim of this review is to briefly highlight the recent advances in the epigenetics of cartilage and potential of HDACs (Histone deacetylases) inhibitors in the therapeutic management of OA. We summarize the recent studies utilizing HDAC inhibitors as potential therapeutics for inhibiting disease progression and preventing the cartilage destruction in OA. HDACs control normal cartilage development and homeostasis and understanding the impact of HDACs inhibitors on the disease pathogenesis is of interest because of its importance in affecting overall cartilage health and homeostasis. These findings also shed new light on cartilage disease pathophysiology and provide substantial evidence that HDACs may be potential novel therapeutic targets in OA.

DNA methylation of the RUNX2 P1 promoter mediates MMP13 transcription in chondrocytes

The Runt-related transcription factor 2 (RUNX2) is critical for bone formation as well as chondrocyte maturation. Matrix metalloproteinase (MMP)-13 is a major contributor to cartilage degradation in osteoarthritis (OA). We and others have shown that the abnormal MMP13 gene expression in OA chondrocytes is controlled by changes in the DNA methylation status of specific CpG sites of the proximal promoter, as well as by the actions of different transactivators, including RUNX2. The present study aimed to determine the influence of the methylation status of specific CpG sites in the RUNX2 promoter on RUNX2-driven MMP13 gene expression in OA chondrocytes. We observed a significant correlation between MMP13 mRNA levels and RUNX2 gene expression in human OA chondrocytes. RUNX2 overexpression enhanced MMP13 promoter activity, independent of the MMP13 promoter methylation status. A significant negative correlation was observed between RUNX2 mRNA levels in OA chondrocytes and the percentage methylation of the CpG sites in the RUNX2 P1 promoter. Accordingly, the activity of the wild type RUNX2 promoter was decreased upon methylation treatment in vitro. We conclude that RUNX2 gene transcription is regulated by the methylation status of specific CpG sites in the promoter and may determine RUNX2 availability in OA cartilage for transactivation of genes such as MMP13.

Differential responses of choroidal melanocytes and uveal melanoma cells to low oxygen conditions

PURPOSE

Tissue culture is traditionally performed at atmospheric oxygen concentration (21%), which induces hyperoxic stress, as endogenous physiologic oxygen tension found in tissues varies between 2% and 9%. This discrepancy may lead to misinterpretation of results and may explain why effects observed in vitro cannot always be reproduced in vivo and vice versa. Only a few studies have been conducted in low physiologic oxygen conditions to understand the development and differentiation of cells from the eye.

METHODS

The aim of this study was to investigate the growth and gene expression profile of melanocytes from the choroid permanently exposed to 21% (hyperoxic) or 3% (physiologic) oxygen with proliferation assays and DNA microarray. The cellular behavior of the melanocytes was then compared to that of cancer cells.

RESULTS

The gross morphology and melanin content of choroidal melanocytes changed slightly when they were exposed to 3% O₂, and the doubling time was statistically significantly faster. There was an increase in the percentage of choroidal melanocytes in the active phases of the cell cycle as observed by using the proliferation marker Ki67. The caveolin-1 senescence marker was not increased in choroidal melanocytes or uveal melanoma cells grown in hyperoxia. In comparison, the morphology of the uveal melanoma cells was similar between the two oxygen levels, and the doubling time was slower at 3% O₂. Surprisingly, gene expression profiling of the choroidal melanocytes did not reveal a large list of transcripts considerably dysregulated between the two oxygen concentrations; only the lactate transporter monocarboxylate transporter (MCT4) was statistically significantly upregulated at 3% O₂.

CONCLUSIONS

This study showed that the oxygen concentration must be tightly controlled in experimental settings, because it influences the subsequent cellular behavior of human choroidal melanocytes.

DNA Methylation Profiling in Chondrocyte Dedifferentiation In Vitro

DNA methylation has emerged as a crucial regulator of chondrocyte dedifferentiation, which severely compromises the outcome of autologous chondrocyte implantation (ACI) treatment for cartilage defects. However, the full-scale DNA methylation profiling in chondrocyte dedifferentiation remains to be determined. Here, we performed a genome-wide DNA methylation profiling of dedifferentiated chondrocytes in monolayer culture and chondrocytes treated with DNA methylation inhibitor 5-azacytidine (5-AzaC). This research revealed that the general methylation level of CpG was increased while the COL-1A1 promoter methylation level was decreased during the chondrocyte dedifferentiation. 5-AzaC could reduce general methylation levels and reverse the chondrocyte dedifferentiation. Surprisingly, the DNA methylation level of COL-1A1 promoter was increased after 5-AzaC treatment. The COL-1A1 expression level was increased while that of SOX-9 was decreased during the chondrocyte dedifferentiation. 5-AzaC treatment up-regulated the SOX-9 expression while down-regulated the COL-1A1 promoter activity and gene expression. Taken together, these results suggested that differential regulation of the DNA methylation level of cartilage-specific genes might contribute to the chondrocyte dedifferentiation. Thus, the epigenetic manipulation of these genes could be a potential strategy to counteract the chondrocyte dedifferentiation accompanying in vitro propagation. J. Cell. Physiol. 232: 1708-1716, 2017. © 2016 Wiley Periodicals, Inc.