Metabolic Action of Thyroid Hormones: Insights from Functional and Proteomic Studies

3,5,3'-triiodo-L-thyronine (T3) modulates development and growth, and in adult life it exerts a profound effect on basal metabolic rate, increasing respiration rate and simultaneously lowering metabolic efficiency. It mainly acts through the coordinated and synergistic modulation of both nuclear and mitochondrial genome expressions giving rise to a complex network of factors and cellular events not yet completely defined. Thus, understanding the effects of T3 requires investigations at several levels [such as genes and gene transcripts (genome and transcriptome), proteins and metabolites, functions and metabolic assessment (proteome and metabolome)]. As yet, the ultimate effects of T3 on tissue-proteomes remain largely unknown. The proteins are excellent targets in disease diagnostics, prognostics, and therapeutics, and therefore proteomic approaches [such as two-dimensional gel electrophoresis (2D-E), two-dimensional liquid chromatography (2-DL), and mass spectrometry (MS)] represent powerful tools for a) the discovery of novel hormone/drug targets and biomarkers, and b) the study of in vivo and in vitro hormone effects on cellular metabolism and protein expressions. Increasingly proteomic techniques are being adopted, in particular to avoid the limitations inherent in the more classical approaches, to solve analytical problems and obtain a more comprehensive identification and characterization of molecular events associated with patho-physiological conditions. Here, we review the new leads emerging from the application of comparative proteomics to the actions of thyroid hormones, and we overview the technologies that can improve the resolution of proteins differing in hydrophobicity, intracellular location, complex formation, and membrane binding.