All-trans Retinoic Acid Disrupts Development in Ex Vivo Cultured Fetal Rat Testes. II: Modulation of Mono-(2-ethylhexyl) Phthalate Toxicity

Abstract

Humans are universally exposed to low levels of phthalate esters (phthalates), which are used to plasticize polyvinyl chloride. Phthalates exert adverse effects on the development of seminiferous cords in the fetal testis through unknown toxicity pathways. To investigate the hypothesis that phthalates alter seminiferous cord development by disrupting retinoic acid (RA) signaling in the fetal testis, gestational day 15 fetal rat testes were exposed for 1-3 days to 10 À6 M all-trans retinoic acid (ATRA) alone or in combination with 10 À6 -10 À4 M mono-(2-ethylhexyl) phthalate (MEHP) in ex vivo culture. As previously reported, exogenous ATRA reduced seminiferous cord number. This effect was attenuated in a concentrationdependent fashion by MEHP co-exposure. ATRA and MEHP-exposed testes were depleted of DDX4-positive germ cells but not Sertoli cells. MEHP alone enhanced the expression of the RA receptor target Rbp1 and the ovary development-associated genes Wnt4 and Nr0b1, and suppressed expression of the Leydig cell marker, Star, and the germ cell markers, Ddx4 and Pou5f1. In co-exposures, MEHP predominantly enhanced the gene expression effects of ATRA, but the Wnt4 and Nr0b1 concentration-responses were nonlinear. Similarly, ATRA increased the number of cells expressing the granulosa cell marker FOXL2 in testis cultures, but this induction was attenuated by addition of MEHP. These results indicate that MEHP can both enhance and inhibit actions of ATRA during fetal testis development and provide evidence that RA signaling is a target for phthalate toxicity in the fetal testis.

E2F1 regulates testicular descent and controls spermatogenesis by influencing WNT4 signaling

“…E2f1-null testes showed a progressive loss of spermatogonia, but the mechanism causing this germ cell loss is unknown. Wnt signaling is activated in stress situations causing cell death; in particular, Wnt4 is upregulated after testicular exposure to genotoxic agents, phthalates and retinoic acid (Pecína-Šlaus, 2010;Spade et al, 2019;Xu et al, 2014). Ectopic activation of WNT4/CTNNB1 signaling in Sertoli cells downregulates SSC activity (Boyer et al, 2012).…”

Paternal exposure to di‐n‐butyl‐phthalate induced developmental toxicity in zebrafish (Danio rerio)

“…The RSP works in several developmental processes, including axial skeleton development, heart outflow tract development, and nervous system development (Ishioka et al, 2011; Kaiser et al, 2003; Stefanovic & Zaffran, 2017). There is evidence demonstrating the relationship between RSP and PAEs (Chen & Reese, 2013, 2016; Spade, Hall, Wortzel, Reyes, & Boekelheide, 2019). Therefore, we hypothesized that developmental defects from paternal DBP exposure may be related to epigenetic modification involving DNA chemical modification in early embryonic development, especially in some important genes in the RSP.…”

REPRODUCTIVE TOXICOLOGY: Environmental exposures, fetal testis development and function: phthalates and beyond

“…Control of RAR signaling is critical for the development and function of the testis. We have shown that phthalates interact with exogenous retinoic acid in the fetal testis, modulating the effects of retinoic acid on cord development (Spade et al 2019b). This hypothesis is consistent with the effects of phthalates on the regulation of genes and proteins involved in the specification of the supporting cell lineage to granulosa or Sertoli-like phenotypes (Wang et al 2015, Spade et al 2019a.…”

“…In fact, many phthalates are predicted in silico to bind to all three human PPAR isoforms. Further, interactions between PPARs and other nuclear receptors, such as RARs, could explain a portion of the phthalate toxicity mechanism (Dufour et al 2003, Spade et al 2019b. Beyond activation or inhibition of PPARs or crosstalk between PPARs and other nuclear receptors, at least two additional MIEs have been proposed in phthalate AOPs, both primarily related to testosterone.…”