Different effects of PPAR-gamma agonists as inducers of "healthy" and "unhealthy" hypertrophic adipocytes

Obesity is an enlargement of adipose tissue which can occur through increased cell number (hyperplasia) or cell size (hypertrophy), causing significant metabolic disturbances. The main regulator of the adipose tissue expansion is the PPARγ that coordinates adipocyte differentiation and maturation. However, different PPARγ agonists can induce opposite effects on hypertrophic adipocytes producing functional (healthy) and dysfunctional (unhealthy) cells. In order to study this different adipocyte behavior, we focused on two different PPARγ agonists: rosiglitazione (ROSI), an anti-diabetic drug, and perfluorooctanoic acid (PFOA), a perfluorinated alkylated environmental obesogen which exposure is associated with clinical diabetes. In this work we evaluated the effects of ROSI and PFOA on adipocytes morphology and biological functions such as adipogenesis, insulin sensitivity and lipolytic response to adrenergic compounds. Methods PFOA (0.1 - 10 μM) or ROSI (1 - 10 nM) were added to 3T3-L1 preadipocytes during the differentiation process. Experiments were carried out on three experimental units each in triplicate and data were considered statistically significant with p value < 0.05 (one-way ANOVA with Tukey’s HSD). Results Oil Red O (ORO) staining showed that ROSI and PFOA treatment produced hypertrophic adipocytes while induced at the same extent hyperplasia. Both induced PPARγ and C/EBP- in a dose-dependent way. Furthermore, while ROSI improved isoprotenerol-stimulated lipolysis and adiponectin gene expression, typical markers of adipocyte functionality, PFOA exposure significantly reduced these parameters. Additionally, ROSI improved glucose homeostasis as effective insulin sensitizers drug, while PFOA impaired P3K/Akt/GLUT signaling and reduced glucose uptake. Adipocytes concomitant treatment with GW9662, a specific PPARγ inhibitor, abolished the PFOA and ROSI effects. We further performed lipid vacuoles analysis focusing on adipocytes morphologic difference exerted by these two PPAR agonist. PFOA exposure led to a greater prevalence of large vacuoles compared to ROSI, while the latter increased small vacuoles number. Additionally, ROSI or PFOA hypertrophic mature adipocytes were induced culturing cells into specific polycarbonate insert transwell and, after complete differentiation, were used to expose preadipocytes during differentiation time. While ROSI exposed cells did not induce mature differentiation, as observed by ORO staining, PFOA hypertrophic cells induced preadipocytes differentiation. Conclusions These findings clearly indicate that PFOA exposure, unlike the ROSI, shifts adipocytes toward an unhealthy phenotype inducing insulin resistance, altered lipolysis, adipokines production, and producing important differentiation stimulus for preadipocytes, all supporting evidence for PFOA and obesity association. Additionally, we observed how the lipid vacuoles size is an important determinant for the adipocyte’s functionality.