Paternal obesity and epigenetic inheritance of breast cancer: The role of systemic effects and transmission to the second generation

Background While genetics explains some familial breast cancer cases, we showed that environmentally-induced epigenetic inheritance of breast cancer can also occur in rodent models. We previously reported that paternal consumption of a high-fat diet and ensuing obesity increased breast cancer susceptibility in the offspring (F1). Nevertheless, it is still unclear whether paternal-induced programming of breast cancer in daughters is associated with systemic alterations or mammary epithelium-specific factors. It also remains to be determined whether the ancestrally programmed breast cancer predisposition in F1 progeny can be transmitted to subsequent generations. Methods Male mice (F0) were fed either a control (CO) diet or an obesity-inducing diet (OID) for seven weeks and then mated with female mice (F0) reared on a CO diet. The resulting offspring (F1), also exclusively fed CO diet, were either used for mammary gland and tumor transplantation surgeries or to generate the F2 generation. To induce the mammary tumors, female mice were treated with 7,12 dimethylbenz[a]anthracene (DMBA). Total RNA extracted from F0 or F1 males sperm was used for small RNA-Seq analysis. Results Mammary glands from F1 CO female offspring exhibited enhanced development when transplanted into OID females [OID(CO-MG)], as shown by higher mammary gland area, epithelial branching and elongation, compared to CO females that received a CO mammary gland [CO(CO-MG)]. Similarly, mammary tumors from F1 CO female offspring transplanted into OID females [OID(CO.T)] displayed improved growth with a higher proliferation/apoptosis rate. We also found that granddaughters (F2) from the OID grand-paternal germline showed accelerated tumor growth compared to COxCO granddaughters (F2). Transmission of breast cancer predisposition to the F2 generation through OID male germline was associated with alterations in specific sperm tRNA fragments (tRF) in both F0 and F1 males. Conclusions Our findings indicate that systemic metabolic and mammary stromal alterations are the most significant contributors to paternal programming of mammary gland development and cancer predisposition in female offspring rather than mammary epithelium confined factors. Our data also show breast cancer predisposition in OID daughters can be transmitted to subsequent generations and could explain some familial cancers, if confirmed in humans. ### Competing Interest Statement The authors have declared no competing interest.