Commentary
Thyroid hormones (THs) are crucial for the standard development and thermo genesis (El-bakry et al., 2010; Ahmed, 2011, 2012a,b, 2013, 2014, 2015a-c, 2016a-d, 2017a-u, 2018a-f; Ahmed et al., 2008, 2010, 2012, 2013a,b, 2014, 2015a,b, 2018a,b; Ahmed and Ahmed, 2012; Ahmed and Incerpi, 2013;Van Hercket al., 2013; Ahmed and El-Gareib, 2014,Incerpi et al., 2014; Candelotti et al., 2015; De Vito et al., 2015; El-Ghareeb et al., 2016; Ahmed and El-Gareib, 2017; Gigena et al., 2017; Bloise et al., 2018), particularly themyogenesis, contractile function, bioenergetic metabolism, the activity of the Na+-K+-ATPase in skeletal myotubes, the sarcoplasmic reticulum Ca2+-ATPase, the differentiation of muscle progenitor cell, and regeneration of the skeletal muscle (Dentice et al., 2010; Schiaffino and Reggiani, 2011; Salvatore et al., 2014; Ortiga-Carvalho et al., 2016; Boelen et al., 2017; Bloise et al., 2018).It is significant to notice that during the normal development of the skeletal muscle, the dynamic changes in the activities of THs can change the fiber type profile and the muscle propriety as well (Simonides and van Hardeveld, 2008; Schiaffino and Reggiani, 2011; Salvatore et al., 2014). In addition, the regular effect of hypothalamus–pituitary–thyroid axis (HPTA) on the homeostasis of the skeletal muscle depending on the thyroid receptors (TRs; α and β), thyroid transporters [monocarboxylate transporters (MCT8 and MCT10)] and thyroid metabolism enzymes (deiodinases; D2, D3) (D’Arezzo et al., 2004; Brockmann et al., 2005; Schwartz and Stevenson, 2007; Irrcher et al., 2008; Cordeiro et al., 2013; Di Cosmo et al., 2013; Boelen et al., 2017; Bloise et al., 2018).On the other hand, the acute, chronic or systemic inflammation can disturb this regulation and change the function of the skeletal muscle (Mebis et al., 2006; Rodriguez-Perez et al., 2008; Kwakkel et al., 2009; Fliers et al., 2014; Bloise et al., 2016; Van den Berghe, 2016). In addition, the expression of MCTs across the plasma membrane may depend on the type of inflammation (Bloise et al., 2018). Also, the disorders in thyroid function can cause the following: (1) reduce the metabolism and glucose level (Ahmed, 2013); (2)disrupt the activities of Ds (DIO2 activity and DIO3 mRNA) (Heemstra et al., 2009;Visser et al., 2009; Marsili et al., 2010;Louzada et al., 2014);(3)diaphragm muscle dysfunction (Herridge et al., 2003); (4) loss of muscle strength (Fredriksson et al., 2005); (5) muscle fatigue (Fredriksson et al., 2006); (6) diminish the mitochondrial content in both legs (Fredriksson and Rooyackers, 2007); (7) perturb the energy production in the respiratory muscle (Fredriksson et al., 2006; Fredriksson and Rooyackers, 2007; Zolfaghari et al., 2015); (8) change the nature of myosin in fast muscle (Butler-Browne et al., 1984; di Maso et al., 2000; Baldwin and Haddad, 2001; Bloise et al., 2018); and(9) muscle weakness and hypoplasia (Schwartz and Stevenson, 2007).
From the above aforementioned results, it can be established that the balance in HPTA may regulate the biological functions of the skeletal muscle. The disorders in the thyroid activity, TRs, Ds or MCTs may impact the myogenesis, the relaxation–contraction rates, metabolism and regeneration of the skeletal muscle. Additional considerations are necessary to confer the effect of thyroid disorders during the gestation on the fetal muscular physiological processes.