Geranylgeraniol Induces PPARγ Expression and Enhances the Biological Effects of a PPARγ Agonist in Adipocyte Lineage Cells

Abstract

Background: The global incidence of diabetes mellitus (DM) has risen precipitously, even in middle- and low-income countries. Peroxisome proliferator-activated receptor γ (PPARγ) plays an important role in the control of cellular glucose metabolism. Activation of PPARγ beneficially results in increased insulin sensitivity. However, the expression of PPARγ is reduced by obesity and several nutritional factors. Here we examined the effect of geranylgeraniol (GGOH), a bioactive compound found naturally in fruits, vegetables, and grains, on the expression and activation of PPARγ.

Materials and methods: C3H10T1/2 mouse embryonic fibroblasts and 3T3-L1 pre-adipocytes were used as in vitro models of adipocyte differentiation and function. Quantitative reverse-transcriptase polymerase chain reaction, western blotting, Oil Red O staining, and luciferase assay were performed to respectively assess mRNA expression, protein levels, lipid droplet formation and transcriptional activity.

Results: GGOH increased the expression of PPARγ in adipocyte lineage cells. GGOH also enhanced adipogenesis induced by rosiglitazone, a thiazolidinedione class PPARγ agonist.

Conclusion: GGOH induces PPARγ expression and enhances the biological effects of a PPARγ agonist in adipocyte lineage cells.

Keywords: Diabetes; adipogenesis; antidiabetic drug; geranylgeranylation; statin.

Figure 1. Geranylgeraniol (GGOH) induces peroxisome proliferator-activated receptor γ (PPARγ) expression. C3H10T1/2 cells were treated with0, 5, 10, 50, or 100 μM GGOH after which the messenger RNA (mRNA) level of Pparg2 (A) was determined by quantitative real-time PCR andprotein levels of PPARγ1 and PPARγ2 (B) were assessed by western blot analysis on day 2. GGOH treatment (50 μM) increased the mRNA levelof Pparg2 in 3T3-L1 cells on day 2 (C). The data are expressed as the mean±SD (n=3). **Significantly different at p<0.01 versus 0 μM GGOH orcontrol (Ctrl; DMSO) treatment.

Figure 2. Geranylgeraniol (GGOH) enhances adipocyte differentiation of C3H10T1/2 mouse embryonic fibroblasts and 3T3-L1 pre-adipocytes.C3H10T1/2 cells were treated with 0, 5, 10, 50, or 100 μM GGOH with or without 10 μM rosiglitazone. The mRNA levels of A: Peroxisomeproliferator-activated receptor γ2 (Pparg2) and B: Fatty acid binding protein 4 (Fabp4) were determined on day 2. C: GGOH treatment (50 μM)enhanced the protein expression of FABP4 induced by 10 μM rosiglitazone in C3H10T1/2 cells after 3 days. D: Cells were treated with 0, 5, 10,50, or 100 μM GGOH with or without 10 μM rosiglitazone. Adipocytes were stained with oil red O on day 7. 3T3-L1 cells were treated with50 μM GGOH with or without 10 μM rosiglitazone and the mRNA levels of E: Pparg2, F: CCAAT-enhancer-binding protein α (Cebpa), G: Fabp4and H: adiponectin, C1Q and collagen domain-containing (Adipoq) were determined after 2 days. I: Adipocytes were stained with oil red O on day7. J: C3H10T1/2 cells were transfected with PPARG2 or an empty vector along with FABP4-luciferase vector and treated with or without 50 μMGGOH. Luciferase activity was determined on day 1. The data are expressed as the mean±SD (n=3). **Significantly different at p<0.01 versus0 μM GGOH or control (Ctrl; DMSO) treatment. Scale bar indicates 20 μm (D and I).

Figure 3. Geranylgeraniol (GGOH) rescues the inhibition of Peroxisome proliferator-activated receptor γ (PPARγ) by simvastatin. A: C3H10T1/2cells were treated with rosiglitazone, GGOH and simvastatin, alone and in combination for 3 days. The mRNA level of Pparg2 was determined byquantitative real-time polymerase chain reaction. The data are expressed as the mean±SD (n=3). *Significantly different at p<0.05. B: Model forGGOH regulation of PPARγ expression