Testicular Gene Expression Profiling following Prepubertal Rat Mono-(2-ethylhexyl) Phthalate Exposure Suggests a Common Initial Genetic Response at Fetal and Prepubertal Ages

Phthalate chemical plasticizers can damage the fetal and postnatal mammalian testis, but several aspects of the injury mechanism remain unknown. Using a genome-wide microarray, the profile of testicular gene expression changes was examined following exposure of postnatal day 28 rats to a single, high dose (1000 mg/kg) of mono-(2-ethylhexyl) phthalate (MEHP). By microarray analysis, approximately 1675 nonredundant genes exhibited significant expression changes; the vast majority were observed at 12 h. Among the 36 genes significantly altered up to the 3-h time point, prominent functional categories were secreted, transcription, and signaling factors. Using quantitative PCR (qPCR), the dose-response of 24 genes was determined after a single MEHP exposure of 10, 100, or 1000 mg/kg. Increasing 114-fold by 12 h at 1000 mg/kg, Thbs1 (thrombospondin 1) showed the highest level of gene induction. The vast majority of genes analyzed by qPCR exhibited significant expression alterations at the lowest dose level. Interestingly, a unique, dose-dependent expression pattern was observed for the transcription factor Nr0b1, steroidogenic genes (Cyp17a1 and StAR), and a cholesterol metabolism gene (Dhcr7). For these genes, the direction of expression change at 10 or 100 mg/kg was opposite that observed at 1000 mg/kg. Gene profiling data at 1000 mg/kg MEHP were phenotypically anchored to increased germ cell apoptosis (6 and 12 h) and an interstitial neutrophil infiltrate (12 h). At 10 or 100 mg/kg MEHP, no testicular morphological changes were detected, but a significant increase in germ cell apoptosis was seen at 6 h. Finally, comparison of the prepubertal MEHP microarray data to similar data from fetal dibutyl phthalate (DBP) exposure showed conservation in both the identities of testicular genes altered and the direction of expression changes. For example, 60% of the genes altered within 3 h of prepubertal MEHP exposure also were changed following acute fetal DBP exposure, and the direction of expression change was highly preserved. These data demonstrate that similar genetic targets are altered following fetal and prepubertal phthalate exposure, suggesting that the initial mechanism of fetal and prepubertal phthalate-induced testicular injury is shared.