Estrogen Receptor 1 Agonist PPT Stimulates Slc2a4 Gene Expression and Improves Insulin-Induced Glucose Uptake in Adipocytes

Abstract

Type 2 diabetes mellitus is characterized by disruption in glycemic homeostasis, involving impaired insulin-induced glucose disposal. For that, reduced glucose transporter GLUT4, encoded by Slc2a4 gene, plays a fundamental role. Conversely, increase in Slc2a4/GLUT4 expression improves glycemic homeostasis. Recent studies have proposed that estradiol is able to modulate Slc2a4 expression, according to distinct effects upon estrogen receptors ESR1/ESR2. We hypothesize that ESR1-agonist effect could stimulate Slc2a4 expression; thus, increasing cellular glucose disposal, which could be beneficial to glycemic control. Differentiated 3T3-L1 adipocytes were treated (24 hours) with selective ESR1- agonist PPT 1,3,5-tris(4-hydroxyphenyl)-4-propyl-1H-pyrazole, selective ESR1-antagonist MPP 1,3-Bis(4- hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1H-pyrazole dihydrochloride, and selective ESR2 agonist DPN 2,3-bis(4-Hydroxyphenyl)-propionitrile, with/without 17β-estradiol (E2). We analyzed Slc2a4 mRNA (real time PCR) and GLUT4 protein (Western blotting) expression, transcriptional activity of the Slc2a4 repressor Nuclear Factor- κB (NF-κB) (electrophoretic mobility shift assay), and cellular glucose disposal (2-deoxi-D-[(3)H]glucose uptake, 2-DG). ESR1-agonist PPT enhanced Slc2a4/GLUT4 expression (~30%) in the absence or presence of 0.1 and 10 nmol/L E2, and decreased the NF-κB binding activity (~50%). Conversely, ESR1-antagonist MPP, together with E2, decreased Slc2a4/GLUT4 expression (20-40%) and increased NF-κB binding activity (~30%). Furthermore, treatment with ESR2- agonist DPN decreased Slc2a4/GLUT4 expression (20-50%). 2-DG uptake was modulated in parallel to that observed in GLUT4 protein. The present results reveal that ESR1 activity enhances, whereas ESR2 activity represses, Slc2a4/GLUT4 expression. These effects are partially mediated by NF-κB, and allow parallel changes in adipocyte glucose disposal. Furthermore, the data provide evidences that ESR1-agonist PPT, as a Slc2a4/GLUT4 enhancer, can be a promising coadjuvant drug for diabetes mellitus therapy.