Thyroid hormone effects on LKB1, MO25, phospho-AMPK, phospho-CREB, and PGC-1α in rat muscle

Abstract

Branvold DJ, Allred DR, Beckstead DJ, Kim HJ, Fillmore N, Condon BM, Brown JD, Sudweeks SN, Thomson DM, Winder WW. Thyroid hormone effects on LKB1, MO25, phospho-AMPK, phospho-CREB, and PGC-1␣ in rat muscle. J Appl Physiol 105: 1218-1227, 2008. First published July 31, 2008 doi:10.1152/japplphysiol.00997.2007.-Expression of all of the isoforms of the subunits of AMP-activated protein kinase (AMPK) and AMPK activity is increased in skeletal muscle of hyperthyroid rats. Activity of AMPK in skeletal muscle is regulated principally by the upstream kinase, LKB1. This experiment was designed to determine whether the increase in AMPK activity is accompanied by increased expression of the LKB1, along with binding partner proteins. LKB1, MO25, and downstream targets were determined in muscle extracts in control rats, in rats given 3 mg of thyroxine and 1 mg of triiodothyronine per kilogram chow for 4 wk, and in rats given 0.01% propylthiouracil (PTU; an inhibitor of thyroid hormone synthesis) in drinking water for 4 wk (hypothyroid group). LKB1 and MO25 increased in the soleus of thyroid hormone-treated rats vs. the controls. In other muscle types, LKB1 responses were variable, but MO25 increased in all. In soleus, MO25 mRNA increased with thyroid hormone treatment, and STRAD mRNA increased with PTU treatment. Phospho-AMPK and phospho-ACC were elevated in soleus and gastrocnemius of hyperthyroid rats. Thyroid hormone treatment also increased the amount of phosphocAMP response element binding protein (CREB) in the soleus, heart, and red quadriceps. Four proteins having CREB response elements (CRE) in promoter regions of their genes (peroxisome proliferatoractivated receptor-␥ coactivator-1␣, uncoupling protein 3, cytochrome c, and hexokinase II) were all increased in soleus in response to thyroid hormones. These data provide evidence that thyroid hormones increase soleus muscle LKB1 and MO25 content with subsequent activation of AMPK, phosphorylation of CREB, and expression of mitochondrial protein genes having CRE in their promoters.adenosine 5Ј-monophosphate-activated protein kinase; acetyl-coenzyme A carboxylase; muscle mitochondria EXPERIMENTAL HYPERTHYROIDISM has previously been demonstrated to increase mitochondrial enzyme content of rat skeletal muscle and other tissues (48, 49). Rat soleus muscle, consisting predominantly of type I, slow-twitch fibers, is much more sensitive than other muscles to this action of thyroid hormones (3, 48), possibly due to increased thyroid hormone receptor expression (3). This model has been used to study some of the basic molecular signaling pathways responsible for this effect of thyroid hormone excess on mitochondrial biogenesis (18,19,33). Hyperthyroidism is one of relatively few conditions that increases metabolic rate and increases expression of mitochondrial proteins in skeletal muscle. Previous studies suggest that the LKB1/AMP-activated protein kinase (AMPK) signaling pathway is important in mitochondrial biogenesis (47,53). In this present study, the adaptation of the LKB1...

Neuronal Protein Tyrosine Phosphatase 1B Deficiency Results in Inhibition of Hypothalamic AMPK and Isoform-Specific Activation of AMPK in Peripheral Tissues

“…In addition, LKB1 and MO25 protein levels are increased in the muscle of PTP1B Ϫ/Ϫ mice, which is likely to contribute to increased AMPK activity. Increased LKB1 expression in skeletal muscle has been reported only in endurance training (59,60) and hyperthyroidism (8). Both of these conditions also are associated with increased MO25 protein levels and enhanced AMPK activity.…”

American Thyroid Association Guide to Investigating Thyroid Hormone Economy and Action in Rodent and Cell Models

“…Chemical inhibition of the thyroid gland can be induced via administration of MMI, PTU, KClO 4 , or NaClO 4 . These drugs can be given through daily intraperitoneal injections (e.g., PTU 1-2 mg/100 g BW, MMI 1-5 mg/ 100 g BW (204)), added to the chow (e.g., 0.02%-0.15% PTU or 0.01% MMI or KClO 4 1.25% (205)) or the drinking water (0.01%-0.1% MMI, 0.01%-0.1% PTU, or 0.1%-1% KClO 4 or NaClO 4 ). A major pitfall of this strategy is that all of these antithyroid drugs have a bitter taste and, when added to the drinking water, consumption should be monitored.…”

“…Typical doses of T 4 or T 3 well tolerated in long-term experiments (2-3 months) are 10-to 25-fold the daily production rate. While food-and water-based drug delivery methods are subject to feeding variability, this may not be critical for studies of chronic thyrotoxicosis; for example, powdered rodent diet containing 3 mg of T 4 and 1 mg of T 3 per kilogram has been used successfully to induce chronic thyrotoxicosis (205). Consideration should be given to more consistent methods such as subcutaneous pumps or pellets (243,244).…”

Role of the AMPK/SREBP-1 pathway in the development of orotic acid-induced fatty liver

“…AMPK is phosphorylated by upstream kinases, among which serine/threonine kinase 11 (LKB1) has been identifi ed as a major AMPK kinase in the liver ( 14 ). LKB1 is considered to be constitutively active; however, in some cases, altered expression or activity of LKB1 is associated with the phosphorylation of AMPK ( 15 ). It is well documented that AMPK phosphorylation inhibits sterol regulatory element-binding protein-1 (SREBP-1), the key transcription factor responsible for fatty acid synthesis, through mammalian target of rapamycin (mTOR) and liver X receptor-␣ (LXR ␣ ) ( 16 ).…”