Abstract 5442: MicroRNAs may mediate multigenerational epigenetic inheritance of mammary cancer risk caused by maternal exposure to high-fat diet during pregnancy
Authors: de Assis Sonia , Laja Ulusola , Warri Anni , Cruz M. Idalia , Jin Lu , Kim Dominic , Hilakivi-Clarke Leena 
Published: August 2012

Maternal dietary exposure to high-fat (HF) during pregnancy increases mammary cancer risk in daughters and granddaughters. It also causes persistent changes in mammary gland morphology in these two HF generations. Our results further show that an increase in mammary cancer risk can be transmitted to HF granddaughters either through the female or male germlines. Disease traits resulting from environmental in utero exposures can be transmitted through multiple generations by epigenetic means. Here, we investigated whether misregulation of expression of specific miRNAs may be involved in mediating the effects of maternal HF exposure during pregnancy on mammary cancer risk in multiple generations of offspring. Pregnant Sprague-Dawley rats were fed isocaloric control or HF diets (fat source: corn oil) throughout pregnancy. The effects on mammary cancer risk in daughters and granddaughters were examined and reported earlier. Total RNA was obtained from mammary glands on postnatal day (PND) 50 from control and HF daughters (F1 generation) and granddaughters (F2 generation). MicroRNA levels were measured using Applied Biosystems TaqManR Array Rodent MicroRNA Card Set v2.0. mRNA expression levels were assessed using q-PCR. Maternal HF exposure during pregnancy increased carcinogen-induced mammary tumorigenesis in both daughters and granddaughters (p=0.049 and p=0.028, respectively). Higher mammary tumor incidence was also observed in the F2 generation even if only one parent had been exposed to HF diet in utero. Fifty one miRNAs were significantly down-regulated on PND50 in mammary glands of HF daughters compared to controls. From these, five miRNAs were also down-regulated in mammary tissue of HF granddaughters compared to controls: let-7c, miR-7a, miR-17, miR-299 and miR-770. Down-regulation of miR-7a and miR-770 was transmitted only through the male germline; i.e., they were expressed at a significantly lower level in F2 daughters of in utero HF exposed fathers, but not HF mothers. Mammary mRNA levels of the polycomb gene, EZH2, a target of let-7c, were up-regulated in both HF daughters and granddaughters compared to controls (p=0.014). Our findings indicate that maternal exposure to HF diet during pregnancy causes a persistent suppression of some miRNAs in the offspring's mammary gland that is transmitted to next generation. The down-regulation of some of these miRNAs was transmitted through the male germline. Moreover, up-regulation of EZH2 transcript, a target gene for let-7c, in mammary tissue of HF daughters and granddaughters, confirms the functional consequence of suppression of this miRNA. Additional studies are needed to elucidate the consequences of suppression of other miRNAs uncovered in this study, and whether they are causally related to increased mammary cancer risk.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5442. doi:1538-7445.AM2012-5442