Context: Skeletal muscle is an important target tissue for thyroid hormone (TH). It is currently unknown which genes are regulated by physiological TH levels. Objective: We examined the effects of L-thyroxine on human skeletal muscle transcriptome. Design: Microarray analysis of transcript levels was performed using skeletal muscle biopsies from patients under euthyroid and hypothyroid conditions. Setting: The study was conducted in a university hospital laboratory. Patients: We studied skeletal muscle obtained from 10 thyroidectomized patients with differentiated thyroid carcinoma on and after 4 wk off L-thyroxine replacement. Mean Outcome Measures: Gene expression changes were measured using microarrays. Results were analyzed using dedicated statistical methods. Results: We detected 607 differentially expressed genes on L-thyroxine treatment, of which approximately 60% were positively and approximately 40% were negatively regulated. Representative genes were validated by quantitative PCR. Genes involved in energy and fuel metabolism were overrepresented among the up-regulated genes, of which a large number were newly associated with thyroid state. L-thyroxine therapy induced a large down-regulation of the primary transcripts of the noncoding microRNA pair miR-206/miR-133b. Conclusion: We demonstrated that physiological levels of TH regulate a myriad of genes in human skeletal muscle. The identification of novel putatively TH-responsive genes may provide the molecular basis of clinical effects in subjects with different TH status. The observation that TH regulates microRNAs reveals a new layer of complexity by which TH influences cellular processes.

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Journal of Clinical Endocrinology and Metabolism
Erasmus MC: University Medical Center Rotterdam

Visser, W.E, Heemstra, K.A, Swagemakers, S.M.A, Ozgur, Z, Corssmit, E.P, Burggraaf, J, … Visser, T.J. (2009). Physiological thyroid hormone levels regulate numerous skeletal muscle transcripts. Journal of Clinical Endocrinology and Metabolism, 94(9), 3487–3496. doi:10.1210/jc.2009-0782