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Thyroid hormone (T₃) rapidly activates p38 and AMPK in skeletal muscle in vivo

Departments of ¹Kinesiology and Health Science and ²Biology, York University, Toronto, Ontario, Canada

Submitted 15 June 2007 ; accepted in final form 18 October 2007

Thyroid hormone (T₃) regulates the function of many tissues within the body. The effects of T₃ have largely been attributed to the modulation of thyroid hormone receptor-dependent gene transcription. However, nongenomic actions of T₃ via the initiation of signaling events are emerging in a number of cell types. This study investigated the ability of short-term T₃ treatment to phosphorylate and, therefore, activate signaling proteins in rat tissues in vivo. The kinases investigated included p38, AMP-activated protein kinase (AMPK), and extracellular signal-regulated kinase (ERK) 1/2. Following 2 h of T₃ treatment, p38 and AMPK phosphorylation was increased in both the slow-twitch soleus and the fast-twitch plantaris muscles. In contrast, ERK1/2 was not activated in either muscle type. Neither p38 nor AMPK was affected in heart. However, AMPK activation was decreased by T₃ in liver. ERK1/2 activation was decreased by T₃ in heart, but increased in liver. Possible downstream consequences of T₃-induced kinase phosphorylation were investigated by measuring cAMP response element binding protein (CREB) and thyroid hormone receptor DNA binding, as well as peroxisome proliferator-activated receptor- coactivator-1 mRNA levels. Protein DNA binding to the cAMP or thyroid hormone response elements was unaltered by T₃. However, peroxisome proliferator-activated receptor- coactivator-1 mRNA expression was increased following 12 h of T₃ treatment in soleus. These data are the first to characterize the effects of T₃ treatment on kinase phosphorylation in vivo. We show that T₃ rapidly modifies kinase activity in a tissue-specific fashion. Moreover, the T₃-induced phosphorylation of p38 and AMPK in both slow- and fast-twitch skeletal muscles suggests that these events may be important in mediating hormone-induced increases in mitochondrial biogenesis in skeletal muscle.

mitochondrial biogenesis; peroxisome proliferator-activated receptor- coactivator-1; signal transduction; adenosine 5'-monophosphate-activated protein kinase; p38 mitogen-activated protein kinase

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