Toxicology

Mapping Gene Expression Changes in the Fetal Rat Testis Following Acute Dibutyl Phthalate Exposure Defines a Complex Temporal Cascade of Responding Cell Types

Abstract
Phthalates are chemical plasticizers used in a variety of consumer products, and in rodents, alter testicular development leading to decreased testosterone synthesis and maldevelopment of the reproductive tract. Here, our goals were to discover a set of biomarker genes that respond early after relatively low dose level dibutyl phthalate (DBP) exposure and map the responding testicular cell types. To identify testicular phthalate biomarker genes, 34 candidate genes were examined by quantitative PCR at 1, 2, 3, or 6 hours after exposure of gestational day 19 rats to DBP dose levels ranging from 0.1 to 500 mg/kg body weight. 12 genes (Ctgf, Cxcl10, Dusp6, Edn1, Egr1, Fos, Ier3, Junb, Nr4a1, Stc1, Thbs1, and Tnfrsf12a) were identified with increased expression by 1 to 3 hours at 100 or 500 mg/kg DBP and 7 of these 12 genes had increased expression by 6 hours at 10 mg/kg DBP. Using in situ hybridization of fetal testis cryosections from DBP exposed rats, the temporal cellular expression of 10 biomarker genes was determined. Genes with a robust response at 1 h (Dusp6, Egr1, Fos, and Thbs1) were induced in peritubular myoid cells. For Egr1 and Fos, the interstitial compartment also showed increased expression at 1 h. Cxcl10 and Nr4a1 were induced by 1 to 3 h in both sparsely located interstitial cells as well as peritubular myoid cells. By 3 h, Stc1 was induced in Leydig cells, and Edn1, Ier3, and Tnfrsf12a were increased in Sertoli cells. These data reveal a complex early cascade of phthalate-induced cellular responses in the fetal testis and, for the first time, suggest peritubular myoid cells are an important proximal phthalate target cell.

Key words: Testis • Toxicology • Leydig cells • Sertoli cells