Figure 1.
Overview of the computational model for steroidogenesis last metabolic steps in a rat granulosa cell.
The transcription and translation events for the three last major enzymes involved in estradiol synthesis, and sex steroid synthesis itself, are modeled, with relevant FSH control, endocrine disrupting chemical (EDC) modulation, or methoxychlor (MXC) aromatase competitive inhibition. Steroids can be transported in and out of cell. In vitro, the exterior compartment corresponds to the culture medium; in vivo it corresponds to the ovary tissue (see Figure 2). Aliases (repeated species labels) are used for clarity but correspond in fact to a unique species.
Figure 2.
Overview of the compartments used to model in vitro (A) or in vivo (B) hormone transports.
In vitro (A), the exterior compartment corresponds to the culture medium. In vivo (B), the ovary tissue is subdivided into three compartments: granulosa cells, “other cells” for thecal and interstitial cells, and extracellular space.
Table 1.
Granulosa cell specific mRNA and protein initial values used.
Table 2.
Model parameter values (for one cell) obtained from direct measurements on granulosa cells in vitro or from the published literature values.
Figure 3.
Experimental data vs predictions for FSH and sex steroid hormones in normal cycling rat.
The black line represents mean model predictions with 95% confidence interval (grey band); points represent our experimental observations (mean of 10 measurements ± standard deviation).
Table 3.
Prior distributions of the model parameters (for one granulosa cell) to be calibrated by MCMC sampling.
Table 4.
Summary statistics of the parameter posterior distributions after Bayesian calibration of the in vitro model.
Table 5.
Model parameter distributions used to describe in vivo variability (in addition to those of Table 4).
Table 6.
Modulation (fold-change) of steroidogenic enzymes mRNA levels and aromatase enzymatic activity following exposure of granulosa cells to selected chemicals.
Figure 4.
Flux analyses of in vitro and in vivo experiments.
Graphs A and B represent the in vitro flux analysis of steroid hormones conversion at 48 h after addition of 200 nM A into the medium, without or with FSH 20 ng/ml. Graphs C, D, and E illustrate the in vivo flux analysis of steroid hormones conversion at several times of the estrus cycle (corresponding to diestrus, proestrus, and estrus stages). The aromatization reaction of A into E1 is taken as the reference reaction for each condition. The flux values for that reference were 7.29×10−9 pmoles/min/cell in vitro without FSH, 8.72×10−8 pmoles/min/cell in vitro with FSH, 6.09×10−9 pmoles/min/cell in vivo in the diestrus stage, 6.17×10−9 pmoles/min/cell in the proestrus stage, and 5.10×10−9 pmoles/min/cell in the estrus stage of the estrous cycle. Values for the other reactions in each condition are relative to the corresponding reference. Arrow thicknesses are proportional to the flux absolute values.
Figure 5.
Experimental data vs predictions of estradiol levels in control and EDC-treated female rats at the diestrus stage.
Experimental data are represented by points (n = 8 for control data, n = 4 for EDC-treated animals data). Statistical distributions of the model predictions are represented by boxplots (showing the distribution quartiles). Control is for atrazine 200 mg/kg, bisphenol A 200 mg/kg, and vinclozolin 100 mg/kg; control 2 is for letrozole 5 mg/kg. ATZ: atrazine; BPA: Bisphenol A; MXC: methoxychlor; VCZ: vinclozolin; LET: letrozole.