Aryl Hydrocarbon Receptor Antagonists Mitigate the Effects of Dioxin on Critical Cellular Functions in Differentiating Human Osteoblast-Like Cells

Abstract

The inhibition of bone healing in humans is a well-established effect associated with cigarette smoking, but the underlying mechanisms are still unclear. Recent work using animal cell lines have implicated the aryl hydrocarbon receptor (AhR) as a mediator of the anti-osteogenic effects of cigarette smoke, but the complexity of cigarette smoke mixtures makes understanding the mechanisms of action a major challenge. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD, dioxin) is a high-affinity AhR ligand that is frequently used to investigate biological processes impacted by AhR activation. Since there are dozens of AhR ligands present in cigarette smoke, we utilized dioxin as a prototype ligand to activate the receptor and explore its effects on pro-osteogenic biomarkers and other factors critical to osteogenesis using a human osteoblast-like cell line. We also explored the capacity for AhR antagonists to protect against dioxin action in this context. We found dioxin to inhibit osteogenic differentiation, whereas co-treatment with various AhR antagonists protected against dioxin action. Dioxin also negatively impacted cell adhesion with a corresponding reduction in the expression of integrin and cadherin proteins, which are known to be involved in this process. Similarly, the dioxin-mediated inhibition of cell migration correlated with reduced expression of the chemokine receptor CXCR4 and its ligand, CXCL12, and co-treatment with antagonists restored migratory capacity. Our results suggest that AhR activation may play a role in the bone regenerative response in humans exposed to AhR activators, such as those present in cigarette smoke. Given the similarity of our results using a human cell line to previous work done in murine cells, animal models may yield data relevant to the human setting. In addition, the AhR may represent a potential therapeutic target for orthopedic patients who smoke cigarettes, or those who are exposed to secondhand smoke or other environmental sources of aryl hydrocarbons.

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin increases the activation of aryl hydrocarbon receptor and is associated with the aggressiveness of osteosarcoma MG-63 osteoblast-like cells

“…Variations on the CXCL12 expressions on the cell lines are also seen ( 39 ). Using AhR antagonist, Yun et al ( 40 ) reported that TCDD induced CXCR4 in an AhR dependent manner. These findings indicate that CXCR4/CXCL12 are different mediated according to cells and microenvironments differences.…”

Endocrine Disruptors as a New Etiologic Factor of Bone Tissue Diseases (Review)

“…The experiments in vivo on the rat lines with different sensitivity to TCDD have established both bone malformation (a shorter bone length) and a dose-dependent effect of this change [ 73 ]. Using a mice and rat model of differentiation of tibia stromal medullary cells it was confirmed that the TCDD disrupting action on bone development and regeneration consists in the decrease of the alkaline phosphatase activity, expression of osteocalcin and bone morphogenetic protein 2, and inhibition of osteoclast differentiation [ 74 ].…”

Role of Endocrine-Disrupting Engineered Nanomaterials in the Pathogenesis of Type 2 Diabetes Mellitus

“…These components control the translocation and activation of glucose transporter proteins (primary effects of insulin) ( 133 ). ENMs can influence the signaling mechanism by interfering with the normal actions of cellular messengers ( 130 , 134 – 137 ).…”