T-2 toxin-induced chondrocyte apoptosis contributes to growth plate damage through Smad2 and Smad3 signaling

Potential involvement of connective tissue growth factor in chondrocytes apoptosis of Kashin-Beck disease

BACKGROUND

Kashin-Beck disease (KBD) is an endemic osteoarthropathy characterized by excessive chondrocytes apoptosis. T-2 toxin exposure has been proved to be its etiology. Connective tissue growth factor (CTGF) exerts a profound influence on cartilage growth and metabolism. We investigated the potential role of CTGF in KBD development and examined CTGF alterations under T-2 toxin stimulation.

METHODS

The levels of CTGF and chondrocyte apoptosis-related markers in cartilage and primary chondrocytes from KBD and control groups were measured using qRT-PCR, Western blotting, immunohistochemistry, and immunofluorescence. We analyzed expression changes of these genes in response to T-2 toxin. Apoptosis rates of chondrocytes induced by T-2 toxin were measured by flow cytometry and TUNEL assay. The active pharmaceutical ingredient targeting CTGF was screened through Comparative Toxicogenomics Database, and molecular docking was performed using AutoDock Tools.

RESULTS

The CTGF levels in KBD cartilage and chondrocytes were significantly elevated and positively associated with the levels of apoptosis-related genes. T-2 toxin exposure increased CTGF and apoptosis-related gene levels in chondrocytes, with apoptosis rates rising alongside T-2 toxin concentration. Curcumin was identified as targeting CTGF and exhibited effective binding. It could down-regulate CTGF, apoptosis-related genes, such as Cleaved caspase 3 and BAX, and also significantly reduce apoptosis rate in chondrocytes treated with T-2 toxin.

CONCLUSION

CTGF plays a crucial role in the development of KBD. Curcumin has shown potential in inhibiting CTGF levels and reducing chondrocyte apoptosis, highlighting its promise as a therapeutic agent for preventing cartilage damage in KBD. Our findings provided valuable insights into the pathogenesis of KBD and could promote the development of novel therapeutic strategies for this debilitating disease.

Tibial Damage Caused by T-2 Toxin in Goslings: Bone Dysplasia, Poor Bone Quality, Hindered Chondrocyte Differentiation, and Imbalanced Bone Metabolism

T-2 toxin, the most toxic type A trichothecene, is widely present in grain and animal feed, causing growth retardation and tissue damage in poultry. Geese are more sensitive to T-2 toxin than chickens and ducks. Although T-2 toxin has been reported to cause tibial growth plate (TGP) chondrodysplasia in chickens, tibial damage caused by T-2 toxin in geese has not been fully demonstrated. This study aims to investigate the adverse effects of T-2 toxin on tibial bone development, bone quality, chondrocyte differentiation, and bone metabolism. Here, forty-eight one-day-old male Yangzhou goslings were randomly divided into four groups and daily gavaged with T-2 toxin at concentrations of 0, 0.5, 1.0, and 2.0 mg/kg body weight for 21 days, respectively. The development of gosling body weight and size was determined by weighing and taking body measurements after exposure to different concentrations of T-2 toxin. Changes in tibial development and bone characteristics were determined by radiographic examination, phenotypic measurements, and bone quality and composition analyses. Chondrocyte differentiation in TGP and bone metabolism was characterized by cell morphology, tissue gene-specific expression, and serum marker levels. Results showed that T-2 toxin treatment resulted in a lower weight, volume, length, middle width, and middle circumference of the tibia in a dose-dependent manner (p < 0.05). Moreover, decreased bone-breaking strength, bone mineral density, and contents of ash, Ca, and P in the tibia were observed in T-2 toxin-challenged goslings (p < 0.05). In addition, T-2 toxin not only reduced TGP height (p < 0.05) but also induced TGP chondrocytes to be disorganized with reduced numbers and indistinct borders. As expected, the apoptosis-related genes (CASP9 and CASP3) were significantly up-regulated in chondrocytes challenged by T-2 toxin with a dose dependence, while cell differentiation and maturation-related genes (BMP6, BMP7, SOX9, and RUNX2) were down-regulated (p < 0.05). Considering bone metabolism, T-2 toxin dose-dependently and significantly induced a decreased number of osteoblasts and an increased number of osteoclasts in the tibia, with inhibited patterns of osteogenesis-related genes and enzymes and increased patterns of osteoclast-related genes and enzymes (p < 0.05). Similarly, the serum Ca and P concentrations and parathyroid hormone, calcitonin, and 1, 25-dihydroxycholecalciferol levels decreased under T-2 toxin exposure (p < 0.05). In summary, 2.0 mg/kg T-2 toxin significantly inhibited tibia weight, length, width, and circumference, as well as decreased bone-breaking strength, density, and composition (ash, calcium, and phosphorus) in 21-day-old goslings compared to the control and lower dose groups. Chondrocyte differentiation in TGP was delayed by 2.0 mg/kg T-2 toxin owing to cell apoptosis. In addition, 2.0 mg/kg T-2 toxin promoted bone resorption and inhibited osteogenesis in cellular morphology, gene expression, and hormonal modulation patterns. Thus, T-2 toxin significantly inhibited tibial growth and development with a dose dependence, accompanied by decreased bone geometry parameters and properties, hindered chondrocyte differentiation, and imbalanced bone metabolism.

Involvement of TLRs/NF-κB/ESE-1 signaling pathway in T-2 toxin-induced cartilage matrix degradation

T-2 toxin, a highly toxic type A monotrichothecene mycotoxin, has been found in many different types of cereals and is considered to be one of the most dangerous naturally occurring forms of food contamination. Globally, consuming grain-based food tainted with T-2 toxin poses significant risks to animal and human health. Prior research has indicated that the presence of T-2 toxin may lead to the demise of chondrocytes and the deterioration of the extracellular matrix of cartilage in degenerative bone and joint conditions, such as Kashin-Beck disease. However, the mechanisms by which T-2 toxin exerts its biological toxicity on the degradation of the extracellular matrix in cartilage are not well understood. In the current study, we found original results that demonstrate an upregulation of Toll-Like Receptors (TLR-2, TLR-4) and ESE-1 expression levels in the articular cartilage of a rat model subjected to T-2 toxin exposure. Furthermore, it was revealed that the exposure to T-2 toxin resulted in an increase in the expression of TLR-2, TLR-4, and ESE-1 in human C28/I2 chondrocytes. The findings of this study indicate that the increased expression of TLR-2, TLR-4, and ESE-1 may contribute to the development of degenerative osteoarthritic disease caused by T-2 toxin. Consistent with our hypotheses, we discovered that T-2 toxin increased the expression of MMP-1 and MMP-13 in human C28/I2 chondrocytes. We used a luciferase reporter gene assay to measure the activity of the ESE-1 promoter and transfected cells with plasmids encoding TLR-2 and TLR-4 to investigate their effects on this activity. TLR-2 and TLR-4 can activate ESE-1 transcriptional gene expression, and this expression is mediated through the NF-κB pathway, additional evidence is provided for the participation of the TLRs/NF-κB/ESE-1 signaling pathway in T-2 toxin-induced cartilage matrix degradation. Together, the findings indicated that the TLRs/NF-κB/ESE-1 signaling pathway played an essential part in T-2 toxin-induced cartilage matrix degradation.