Abstract
The maxilla and masseter muscles are components of the stomatognathic system involved in chewing, which is frequently affected by physical forces such as gravity, and by dental, orthodontic and orthopedic procedures. Thyroid hormones (TH) are known to regulate the expression of genes that control bone mass and the oxidative properties of muscles; however, little is known about the effects of TH on the stomatognathic system. This study investigated this issue by evaluating: i) osteoprotegerin (OPG) and osteopontine (OPN) mRNA expression in the maxilla and ii) myoglobin (Mb) mRNA and protein expression, as well as fiber composition of the masseter. Male Wistar rats (~250 g) were divided into thyroidectomized (Tx) and sham-operated (SO) groups (N = 24/group) treated with T3 or saline (0.9%) for 15 days. Thyroidectomy increased OPG (~40%) and OPN (~75%) mRNA expression, while T3 treatment reduced OPG (~40%) and OPN (~75%) in Tx, and both (~50%) in SO rats. Masseter Mb mRNA expression and fiber type composition remained unchanged, despite the induction of hypo- and hyperthyroidism. However, Mb content was decreased in Tx rats even after T3 treatment. Since OPG and OPN are key proteins involved in the osteoclastogenesis inhibition and bone mineralization, respectively, and that Mb functions as a muscle store of O2 allowing muscles to be more resistant to fatigue, the present data indicate that TH also interfere with maxilla remodeling and the oxidative properties of the masseter, influencing the function of the stomatognathic system, which may require attention during dental, orthodontic and orthopedic procedures in patients with thyroid diseases.
Highlights
The activity of bone cells is regulated by mechanical and hormonal factors [1]
Effect of thyroid hormone on the OPG and OPN gene expression in the maxilla The effect of Thyroid hormones (TH) on OPG mRNA expression in the maxilla is presented in Figure 1A, which shows that Tx induced a 40% increase in OPG mRNA content, and that T3 treatment reduced it to SO levels
We used the maxilla and masseter muscles to evaluate the effects of TH on the stomatognathic system
Summary
The activity of bone cells is regulated by mechanical and hormonal factors [1]. Thyroid hormones (TH) are known to participate in bone turnover and their effects have been well established [2].The expression of proteins such as osteoprotegerin (OPG) and osteopontine (OPN), is reduced by TH [3,4], in contrast to osteocalcin, alkaline phosphatase and bone morphogenetic proteins, whose expression is increased [5,6,7]. The activity of bone cells is regulated by mechanical and hormonal factors [1]. Bone resorption is associated with decreased OPG and OPN expression. OPN is an extracellular matrix protein synthesized and released from osteoblasts and osteocytes, responsible for maintaining calcium in the bone matrix, an essential event for mineralization [10]. It presents a highly conserved arginyl-glycyl-aspartic acid motif that mediates cell attachment to the extracellular matrix via the alpha V beta 3 integrin [11]. OPG and OPN are excellent markers for the evaluation of the effect of TH on bone
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