Pluto Bioinformatics

GSE155435: Exposure to tert-butylphenyl diphenyl phosphate, an organophosphate ester flame retardant and plasticizer, alters hedgehog signaling in ex vivo murine limb bud cultures

Bulk RNA sequencing

Organophosphate esters (OPEs) have become widely used as flame retardants since the global phase out of polybrominated diphenyl ethers (PBDEs). Previously, we demonstrated that some OPEs, such as tert-butylphenyl diphenyl phosphate (BPDP), were more detrimental to endochondral ossification in ex vivo murine limb bud cultures than one of the major PBDEs that they replaced, 2,2',4,4'-tetrabromodiphenyl ether (BDE-47). Here we used a transcriptomic approach to elucidate the mechanism of action of BPDP in the developing limb. Limb buds collected from gestation day 13 CD1 mouse embryos were cultured for 3 or 24 hours in the presence of vehicle, 1 M, or 10 M BPDP. RNA sequencing (RNA-seq) analyses revealed that exposure to 1 M BPDP for 24 hours increased the expression of 5 transcripts, including Ihh, and decreased 14 others, including Gli1, Ptch1, Ptch2, and other targets of Hedgehog (Hh) signaling. Pathway analysis inferred the inhibition of Hh signaling. Attenuation of Hh signaling activity began earlier and reached a greater magnitude after exposure to 10 M BPDP. Since this pathway is part of the regulatory network governing endochondral ossification, we used a known Hh agonist, purmorphamine, to determine the contribution of Hh signaling inhibition to the negative impact of BPDP on endochondral ossification. Co-treatment of limbs with purmorphamine rescued the detrimental morphological changes in the cartilage template induced by BPDP exposure though it did not restore the expression of key transcription factors, Runx2 and Sp7, to control levels. These data highlight Hh signaling as a developmentally important pathway vulnerable to environmental chemical exposures. SOURCE: Barbara,F.,Hales (barbara.hales@mcgill.ca) - McGill University