Mice Exposed To Early Life Stress Display Sex-Specific Upregulation Of Leptin Gene Expression In Adipose Tissue

Epidemiological studies have established early life stress (ELS) as an independent risk factor for increased BMI and cardio‐metabolic disease later in life. We have previously shown that a mouse model of ELS, Maternal Separation and Early Weaning (MSEW), increases adiposity in weanlings and exacerbates high fat diet (HFD)‐induced fat expansion in a sex‐specific manner. Therefore, the aim of this study was to investigate the sex‐specific effects of MSEW on adipocyte‐derived production of important hormones for body weight homeostasis, such as leptin and adiponectin. MSEW was performed by separating the pups from the dam for 4 to 8 hours during postnatal days (PD) 2 to 16, and weaned on PD 17. Control mice remained undisturbed and were weaned on PD 21. Following, eight‐week‐old mice were then fed on either a low fat diet (LFD, n=6) or HFD (10 or 60 % Kcal from fat, n=6) for 12 weeks. Each litter was represented by one mice of each sex randomly assigned to each diet. Body composition trajectory was assessed by EchoMRI. At the end of the experiment, mice were sacrificed for adipose tissue collection. Leptin and adiponectin gene expression was performed in gonadal white adipose tissue (gWAT) and subcutaneous WAT (scWAT). After 12 weeks of HFD, male MSEW mice showed increased BW compared with controls (47.9 ± 1.1 vs. 40.2 ± 2.6 g, p<0.05) as well body adiposity (36.7 + 1.1 vs. 22.2 ± 4.1 % body fat, respectively). In female MSEW mice fed a HFD, but not in males, the gene expression of leptin in gWAT was significantly upregulated compared with controls (5.0 ± 0.5 vs. 3.6 ± 0.5, p<0.05), but not in scWAT (2.1 ± 0.6 vs. 1.5 ± 0.5, p<0.05). Despite sex‐specific changes in adiponectin gene expression in response to HFD, there was not a significant effect due to MSEW. To begin to address the mechanism by which MSEW increases leptin expression in a sex‐specific manner, we analyzed the site‐specific methylation of the leptin promoter in gWAT from mice fed a HFD (n=4). The methylation landscape in the leptin promoter was different between male and female mice. However, we found that CpG sites 3 and 15 were significantly hypomethylated only in fat from female MSEW mice comparted to controls (site 3: 21±1 vs. 52±1 %5mC, p<0.05; site 15: 84±1 vs. 100 %5mC, p<0.05). Both sites in the leptin promoter are strong areas for transcription factor binding. In addition, DNMT3A was upregulated in MSEW mice (p<0.05). Taken together, our current working hypothesis is focused on elucidating whether exposure to MSEW may promote the binding of specific transcription factors that upregulate leptin gene expression in a depot and sex‐specific manner.