Associations between prenatal phthalate exposure and sex-typed play behavior in preschool age boys and girls.

Phthalates, a class of chemicals found widely in consumer products including plastic toys, food contaminants and food packaging, personal care products, cosmetics, air fresheners, and some medications, have been shown to be anti-androgenic in numerous laboratory and epidemiological studies. In a prior cohort enrolled in 2000-2002, we observed associations between prenatal urinary concentrations of di-ethyl hexyl phthalate (DEHP) and dibutyl phthalate (DBP) metabolites and less male-typed play behavior in preschool age boys. The aim of this study was to examine phthalate exposure in pregnancy in relation to play behavior at age 4 years in a larger cohort of pregnant women enrolled in The Infant Development and the Environment Study (TIDES) between 2010 and 2012 at four study sites (Minneapolis, MN; Rochester, NY; San Francisco, CA; Seattle, WA). Maternal urinary metabolites of DEHP, DiBP, DnBP, BBzP, and DEP were measured during the first (n=498) and third trimester (n=468) and mothers completed the Preschool Activities Inventory (PSAI), a validated maternal questionnaire designed to assess child toy preference and sex-typed play behavior when children were 4-5 years of age. After adjusting for child age, maternal education, race, urine dilution, parental attitudes about opposite sex-typed play behavior, and presence of a same sex older sibling, we observed associations between first trimester (mean 10.7±2.1 weeks gestation) (log10) SpG-adjusted MnBP, MiBP, and MBzP and lower masculine scores in boys (ß-coefficient [95% confidence intervals]: MnBP -2.18, [-4.16, -0.20]), MiBP -2.1[-4.3,0.1], and MBzP -2.42 [-4.12, -0.71]). In girls, first trimester maternal urinary MBzP was associated with lower masculine scores (-2.12 [-3.98,-0.25]), while third trimester (mean 32.8±3.0 weeks gestation) maternal urinary MiBP was associated with higher masculine scores (2.69 [0.68,4.70]). Third trimester maternal urinary phthalate levels were not associated with play behavior in boys. These findings in boys are largely consistent with previous studies that report that prenatal phthalate exposure is associated with less masculine play behavior. No associations in girls have been previously reported.

Early prenatal sex steroids and sex-typed play behavior at 4 years of age.

During pregnancy, estrogens and testosterone influence brain development, resulting in sex-typical behavioral phenotypes. Prenatal testosterone exposure is associated with more male-typical behaviors in rodents, monkeys, and humans; however, few studies have examined the relationship between maternal sex hormones within the normal range and sex-dimorphic behaviors. In this study, we examined associations between prenatal estrogens and testosterone and sex-typical play in The Infant Development and the Environment Study (TIDES), a multicenter pregnancy cohort. We collected prenatal serum during the first trimester (mean=11.1 ± 2.6 weeks) and assessed child play behavior using the maternally completed Pre-School Activities Inventory (PSAI) at a mean age of 4.5 ± 0.3 years. This analysis includes mother-child pairs with complete data on hormones, play behavior, and covariates (n = 192 boys and 207 girls). No associations were seen between testosterone and PSAI scores in boys or girls or between estrogens and PSAI scores in boys. In girls, we observed an inverse relationship between feminine PSAI scores and both estradiol (E2) and estriol (E3) in multivariable linear regression analyses (E2: -0.11 [95% CI -0.20, -0.02]; E3: -0.44 [95% CI -0.83,-0.04]). Because the relationship between sex hormones and PSAI scores appeared nonlinear, we fit piecewise regression models to better fit the data and identify inflection points (point at which there is a significant change in slope). Piecewise regression analyses yielded inverse associations between masculine PSAI scores and estrone (E1) at values of E1 > 1340 pg/mL and E2 at values of E2 > 2870 pg/mL in girls. Further studies are needed to better understand the role of prenatal sex steroids on sexually dimorphic behavior.

Neuronal brain-derived neurotrophic factor is synthesized in excess, with levels regulated by sortilin-mediated trafficking and lysosomal degradation.

Brain-derived neurotrophic factor (BDNF) regulates neuronal differentiation, synaptic plasticity, and morphology, and modest changes in BDNF levels results in complex behavioral phenotypes. BDNF levels and intracellular localization in neurons are regulated by multiple mechanisms, including use of distinct promoters, mRNA and protein transport, and regulated cleavage of proBDNF to mature BDNF. Sortilin is an intracellular chaperone that binds to the prodomain of BDNF to traffic it to the regulated secretory pathway. However, sortilin binds to numerous ligands and plays a major role in mannose 6-phosphate receptor-independent transport of lysosomal hydrolases utilizing motifs in the intracellular domain that mediate trafficking from the Golgi and late endosomes. Sortilin is modified by ectodomain shedding, although the biological implications of this are not known. Here we demonstrate that ADAM10 is the preferred protease to cleave sortilin in the extracellular stalk region, to release the ligand binding sortilin ectodomain from the transmembrane and cytoplasmic domains. We identify sortilin shedding at the cell surface and in an intracellular compartment. Both sortilin and BDNF are trafficked to and degraded by the lysosome in neurons, and this is dependent upon the sortilin cytoplasmic tail. Indeed, expression of the sortilin ectodomain, which corresponds to the domain released after shedding, impairs lysosomal targeting and degradation of BDNF. These findings characterize the regulation of sortilin shedding and identify a novel mechanism by which sortilin ectodomain shedding acts as a regulatory switch for delivery of BDNF to the secretory pathway or to the lysosome, thus modulating the bioavailability of endogenous BDNF.