Species-Specific Dibutyl Phthalate Fetal Testis Endocrine Disruption Correlates with Inhibition of SREBP2-Dependent Gene Expression Pathways

ArticleinToxicological Sciences 120(2):460-74 · March 2011with12 Reads
DOI: 10.1093/toxsci/kfr020 · Source: PubMed
Abstract
Fetal rat phthalate exposure produces a spectrum of male reproductive tract malformations downstream of reduced Leydig cell testosterone production, but the molecular mechanism of phthalate perturbation of Leydig cell function is not well understood. By bioinformatically examining fetal testis expression microarray data sets from susceptible (rat) and resistant (mouse) species after dibutyl phthalate (DBP) exposure, we identified decreased expression of several metabolic pathways in both species. However, lipid metabolism pathways transcriptionally regulated by sterol regulatory element-binding protein (SREBP) were inhibited in the rat but induced in the mouse, and this differential species response corresponded with repression of the steroidogenic pathway. In rats exposed to 100 or 500 mg/kg DBP from gestational days (GD) 16 to 20, a correlation was observed between GD20 testis steroidogenic inhibition and reductions of testis cholesterol synthesis endpoints including testis total cholesterol levels, Srebf2 gene expression, and cholesterol synthesis pathway gene expression. SREBP2 expression was detected in all fetal rat testis cells but was highest in Leydig cells. Quantification of SREBP2 immunostaining showed that 500 mg/kg DBP exposure significantly reduced SREBP2 expression in rat fetal Leydig cells but not in seminiferous cords. By Western analysis, total rat testis SREBP2 levels were not altered by DBP exposure. Together, these data suggest that phthalate-induced inhibition of fetal testis steroidogenesis is closely associated with reduced activity of several lipid metabolism pathways and SREBP2-dependent cholesterologenesis in Leydig cells.
    • "Many of the C2 to C7 di-ortho PEs reduce fetal male testicular testosterone production (T PROD) and gene expression levels resulting in adverse effects that are seen only after birth (Furr et al., 2014). More than 25 to 30 genes have been shown to date to display reduced expression levels in the fetal testis after exposure to PEs, including genes involved in steroid hormone synthesis and transport, Insl3 hormone synthesis (Hannas et al., 2012) and cholesterol synthesis (Johnson et al., 2011) (Gray et al, in prep). A recent study from our laboratory (Hannas et al., 2011a) demonstrated that the PE ED 50 values for anogenital distance at birth and retained nipples in infant male rats were three to five fold higher than the ED 50 value for reductions in testosterone production and testis gene expression with dipentyl phthalate (DPeP) being the most potent of the active PEs. "
    [Show abstract] [Hide abstract] ABSTRACT: Phthalate esters (PEs) constitute a large class of compounds that are used for many consumer product applications. Many of the C2 to C7 di-ortho PEs reduce fetal testicular hormone and gene expression levels in rats resulting in adverse effects seen later in life but it appears that relatively large reductions in fetal testosterone (T) levels and testis gene expression may be required to adversely affect reproductive development (Hannas et al., 2012). The objectives of the current study were 1) to model the relationships between changes in fetal male rat plasma T (PT), T levels in the testis (TT), T production (PROD) and testis gene expression with the reproductive malformation rates, and 2) to quantify the "biologically relevant reductions" (BRRs) in fetal T necessary to induce adverse effects in the offspring.In the fetal experiment, Harlan SD rats were dosed with dipentyl phthalate (DPeP) at 0, 11, 33, 100 and 300 mg/kg/d from gestation day (GD) 14 to 18 and fetal testicular T, plasma T levels, and T Prod and gene expression were assessed on GD 18. In the postnatal experiment, rats were dosed with DPeP from GD 8-18 and reproductive development was monitored through adulthood.The dose response curves for TT levels (ED50 = 53 mg/kg) and T PROD (ED50 = 45 mg/kg) were similar, whereas PT was reduced at ED50 = 19 mg/kg. When the reductions in TPROD and Insl3 mRNA were compared to the postnatal effects of in utero DPeP, dose-related reproductive alterations were noted when T PROD and Insl3 mRNA were reduced by >45% and 42%, respectively. The determination of BRR levels may enable risk assessors to utilize fetal endocrine data to help establish points of departure for quantitative risk assessments.
    Full-text · Article · Oct 2015
    • "In particular, the increase in SREBP-1c expression, described also by Kim et al. [13], can be considered as an LXRa-mediated response, whereas the decrease in LGK expression as a SREBP-mediated response. In fact, being LGK a direct target gene of SREBP [44] (and consequently an indirect target gene of LXR), whose transcription activity is inhibited by this class of molecules [45], their interaction produces a decrease in LGK expression. Accordingly, being T0901317 a specific LXR binder, it causes the increase in SREBP expression and, subsequently/indirectly, the increase in LGK expression (Fig. 4, in agreement with Kim et al. [13]). "
    [Show abstract] [Hide abstract] ABSTRACT: Liver X receptor is a ligand-activated transcription factor, which is mainly involved in cholesterol homeostasis, bile acid and triglycerides metabolism, and, as recently discovered, in the glucose metabolism by direct regulation of liver glucokinase. Its modulation by exogenous factors, such as drugs, industrial by-products and chemicals is documented. Owing to the abundance of these synthetic molecules in the environment, and to the established target role of this receptor, a number of representative compounds of phthalate, organophosphate and fibrate classes were tested as ligands/modulators of human liver X receptor, using an integrated approach, combining an in silico molecular docking technique with an optical SPR biosensor binding study. The compounds of interest were predicted and proved to target the oxysterols-binding site of human LXRα with measurable binding kinetic constants and with affinities ranging between 4.3×10(-7)-4.3×10(-8) M. Additionally, non-cytotoxic concentration of these chemicals induced relevant changes in the LXRα gene expression levels and other target genes (SREBP-1c and LGK) in human liver hepatocellular carcinoma cell line (HepG2), as demonstrated by q-RT-PCR. Copyright © 2015. Published by Elsevier Ltd.
    Full-text · Article · Apr 2015
    • "Like many EDCs, also phthalate and their metabolites have been suggested to interfere with normal steroidogenesis, suppressing the expression of steroidogenic enzymes (Moody et al., 2013 ), disrupting the regulation of cholesterol and lipid homeostasis or insulin signaling (Barlow et al., 2003; Liu et al., 2005; Knez, 2013). Phthalate exposure reduces testis cholesterol and cholesterol-containing lipid droplets in rat FLCs (Barlow et al., 2003; Lehmann et al., 2004; Johnson et al., 2011 Johnson et al., , 2012). Specifically, the immediate event precipitating Leydig cell testosterone attenuation appears to be the reduced expression of mRNA and protein within the cholesterol trafficking/biosynthesis and steroidogenic enzymatic pathways (Johnson et al., 2012). "
    [Show abstract] [Hide abstract] ABSTRACT: Endocrine disrupting chemicals (EDCs) are identified for their ability to perturb the homeostasis of endocrine system and hormonal balance. The male reproductive system is under close control of hormones and each change in their concentration and time of exposition and action can induce a deregulation of its physiology. In this review we summarize the most recent studies on two main categories of EDCs with different action: the estrogenic bisphenol A and alkylphenols and the anti-androgenic phthalates. This review describes the main effects of these substances on male reproductive system.
    Full-text · Article · Feb 2015
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