Endocrine Abstracts

The growing obesity rate is not only the result of sedentary lifestyle and Western diet, but environmental exposure to endocrine disrupting chemicals (EDCs) may also contribute to this global phenomenon. Some EDCs called obesogens target central pathways regulating food intake and energy expenditure, in particular in the hypothalamus. Indeed, this brain region is the central regulator of many functions including thyroid axis and metabolism. It consists of various nuclei, each having a unique role in regulating these functions. Organisms are especially vulnerable to EDCs during the perinatal period when hormonal signaling orchestrates the setup of endocrine and metabolic axes. In this context, we explored the combined effect of perinatal exposure to the flame-retardant tetrabromobisphenol A (TBBPA), an EDC well known to perturb thyroid hormone signaling, and high fat-high sucrose diet (HFHS, mimics Western diet) at adult age, on the hypothalamic transcriptome. We compared the responses to these treatments on two mouse strains with different metabolic and thyroid status, the C57BL/6J mice and the WSB/EiJ mice. Pregnant dams received 10 mg/kg/d TBBPA or vehicle for 4 weeks (last week of gestation through lactation). The progeny followed a HFHS diet from 2 to 6 months of age. We compared four groups for each strain: vehicle+control diet, vehicle+HFHS diet, TBBPA+control diet and TBBPA+HFHS diet. We used the cutting-edge technology of spatial transcriptomics (10X Genomics), which add a spatial localization to total transcriptome analyses. We measured the whole transcriptome activity, mapped to the relevant hypothalamic regions to identify the specific transcriptional pathways regulated in each hypothalamic nucleus. We first had to optimize this technology in order to adapt the analysis workflow to the specificity of the physiological regulations that we were looking for. This optimization step allowed us to identify different clusters which were exactly aligned with the hypothalamic nuclei identified by histology. We were thus able to identify a specific transcriptional signature for each hypothalamic nucleus. The second step was to establish a workflow to compare these transcriptional signatures between the different study groups within and between each strain. The spatial transcriptomics analysis overcomes the low-resolution of bulk RNAseq in a complex tissue-context and resolves the spatial origin of the signal as opposed to single cell RNAseq. This powerful technology allows us to identify the molecular pathways specifically affected by the different treatments in the different hypothalamic nuclei involved in the regulation of thyroid axis and metabolism. This will unravel the mechanisms by which the perinatal TBBPA exposure coupled to HFHS diet interfere with the setpoint adjustment of the thyroid axis or other hormonal pathways, and therefore alter the adult’s ability to cope with metabolic challenges.