Retinol binding protein 4 mediates MEHP-induced glucometabolic abnormalities in HepG2 cells

Epidemiological and experimental data have implicated the role of di(2-ethylhexyl) phthalate (DEHP) and its metabolite mono(2-ethylhexyl) phthalate (MEHP) in the pathogenesis of metabolic syndrome, including the impairment of hepatic glucose metabolism. To elucidate the underlying mechanism by which DEHP or MEHP perturbs hepatic glucose homeostasis, we compared the effect of DEHP (0-200 μM) and MEHP (0-200 μM) on glucose metabolism in HepG2 cells. In this study, we found that MEHP can induce more severe impairments in glucose homeostasis than DEHP can; these include increased hepatic gluconeogenesis via receptor substrate-1/protein kinase B/fork-head box protein O1 (IRS-1/AKT/FOXO1)-mediated phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6PC) up-regulation, as well as decreased hepatic glycogen synthesis via glucokinase (GCK) inhibition and IRS-1/AKT/glycogen synthase kinase-3β (GSK-3β)-mediated glycogen synthase (GYS) inactivation. Additionally, our results demonstrated that retinol binding protein 4 (RBP4), an insulin resistance-inducing factor, plays a critical role in the MEHP-induced disorder of glucose homeostasis and the dysfunction of insulin signaling transduction, whereas the deletion of RBP4 by the clustered regularly interspaced short palindromic repeats-Cas9 (CRISPR/Cas9) significantly reversed these toxic effects. Although these should be interpreted with caution in view of limited in vivo evidence, the present study provides the first in vitro evidence for potential involvements of RBP4 in disturbance of glucose homeostasis in the MEHP-treated HepG2 cells.