Thiazolidinediones (PPARγ agonists) but not PPAR α agonists increase IRS‐2 gene expression in 3T3‐L1 and human adipocytes¹

Abstract

Thiazolidinediones (TZD) improve insulin sensitivity in human as well as in different animal models of insulin resistance and Type 2 diabetes. However, no clear link to the insulin signaling events has been identified. Using differentiated 3T3-L1 adipocytes, we found that TZD rapidly and markedly increased IRS-2 gene expression. This effect was specific for PPARgamma agonists and was not seen with PPARalpha agonists. It was rapidly induced (within 4 h) and maintained throughout the observation period of 48 h. It was also concentration dependent (EC50 approximately 50 nM) and not inhibited by cycloheximide, suggesting a direct effect on the IRS-2 promoter. There was no evidence that TZD altered IRS-2 mRNA stability, supporting that the increased mRNA levels were due to an increased gene transcription. IRS-2 protein expression was increased approximately 30% after 48 h and approximately 50% after 96 h. No effects of TZD were seen on IRS-1, PKB/Akt, or GLUT4 gene expression. TZD also increased IRS-2 mRNA levels in cultured human adipose tissue. These data show the first direct link between TZD and a critical molecule in insulin's signaling cascade in both 3T3-L1 and human adipocytes, and indicate a novel mode of action of these compounds.

Identification of a region in the human IRS2 promoter essential for stress induced transcription depending on SP1, NFI binding and ERK activation in HepG2 cells

“…In 3T3-L1 adipocytes, thiazolidinediones induced expression of the IRS2 gene through PPARg activation (Smith et al 2001). In our hands we could not find any activating effects of rosiglitazone using our IRS2 promoter reporter plasmids (data not shown).…”

“…6A, we were not able to induce IRS2 promoter activity in HepG2 cells with increasing amounts of glucose. Thiazolidinediones, which promote insulin sensitivity in humans by PPARg activation increased IRS2 gene expression in 3T3-L1 cells and human adipocytes (Smith et al 2001). Moreover, pioglitazone induced IRS1 but not IRS2 expression in muscle (Hammarstedt & Smith 2003).…”

WY-14643 and 9-cis-retinoic acid induce IRS-2/PI 3-kinase signalling pathway and increase glucose transport in human skeletal muscle cells: differential effect in myotubes from healthy subjects and Type 2 diabetic patients

“…We are currently investigating the effects of other activators of PPARα to confirm its implication in muscle cells. It has also been demonstrated that IRS-2 [42] and p85α PI 3-kinase [17] gene expression can be induced by activation of PPARγ in human adipocytes and that this effect leads to improved insulin signalling [17]. The ligands of PPARγ were inefficient in myotubes, probably due to the low expression level of this nuclear receptor in muscle [18].…”

Interleukin-6 (IL-6) Induces Insulin Resistance in 3T3-L1 Adipocytes and Is, Like IL-8 and Tumor Necrosis Factor-α, Overexpressed in Human Fat Cells from Insulin-resistant Subjects

“…Pierce, NCI, National Institutes of Health) and the IRS-1 probe of a PCR-amplified 409-bp fragment as described (41). Protein and RNA blots were scanned using a Personal Densitometer (Amersham Biosciences) and analyzed using ImageQuant software provided by the manufacturer.…”