T2 Improves Insulin Resistance
Pieter de Lange1, Federica Cioffi2, Rosalba Senese1, Maria Moreno2, Assunta Lombardi3, Elena Silvestri2, Rita De Matteis4, Lillà Lionetti3, Maria Pina Mollica3, Fernando Goglia2⇓ and Antonia Lanni1⇓
1 Dipartimento di Scienze della Vita, Seconda Università degli Studi di Napoli, Caserta, Italy
2 Dipartimento di Scienze per la Biologia, la Geologia e l’Ambiente, Università degli Studi del Sannio, Benevento, Italy
3 Dipartimento delle Scienze Biologiche, Sez. Fisiologia ed Igiene, Università degli Studi di Napoli “Federico II,” Napoli, Italy
4 Dipartimento di Scienze Biomolecolari, Università di Urbino “Carlo Bo,” Urbino, Italy
Corresponding author: Fernando Goglia, email@example.com, or Antonia Lanni, firstname.lastname@example.org.
OBJECTIVE High-fat diets (HFDs) are known to induce insulin resistance. Previously, we showed that 3,5-diiodothyronine (T2), concomitantly administered to rats on a 4-week HFD, prevented gain in body weight and adipose mass. Here we investigated whether and how T2 prevented HFD-induced insulin resistance.
RESEARCH DESIGN AND METHODS We investigated the biochemical targets of T2 related to lipid and glucose homeostasis over time using various techniques, including genomic and proteomic profiling, immunoblotting, transient transfection, and enzyme activity analysis.
RESULTS Here we show that, in rats, HFD feeding induced insulin resistance (as expected), whereas T2 administration prevented its onset. T2 did so by rapidly stimulating hepatic fatty acid oxidation, decreasing hepatic triglyceride levels, and improving the serum lipid profile, while at the same time sparing skeletal muscle from fat accumulation. At the mechanistic level, 1) transfection studies show that T2 does not act via thyroid hormone receptor β; 2) AMP-activated protein kinase is not involved in triggering the effects of T2; 3) in HFD rats, T2 rapidly increases hepatic nuclear sirtuin 1 (SIRT1) activity; 4) in an in vitro assay, T2 directly activates SIRT1; and 5) the SIRT1 targets peroxisome proliferator–activated receptor (PPAR)-γ coactivator (PGC-1α) and sterol regulatory element–binding protein (SREBP)-1c are deacetylated with concomitant upregulation of genes involved in mitochondrial biogenesis and downregulation of lipogenic genes, and PPARα/δ-induced genes are upregulated, whereas genes involved in hepatic gluconeogenesis are downregulated. Proteomic analysis of the hepatic protein profile supported these changes.
CONCLUSIONS T2, by activating SIRT1, triggers a cascade of events resulting in improvement of the serum lipid profile, prevention of fat accumulation, and, finally, prevention of diet-induced insulin resistance.
Received February 16, 2011.
Accepted July 28, 2011.