SAT-588 Role of Adipose Tissue in Reproduction, Mammary Gland Development, Function and Cancer

To investigate the role of adipose tissue in the function of the mammary gland (MG) and reproductive system, we have examined lipodystrophic (LD) mice. LD mice of both sexes are sterile, but fertility was restored in both sexes with leptin injections. In addition, leptin was only needed for initial stages of pregnancy and not for parturition. A transplant of mouse embryonic fibroblasts (MEFs) led to the formation of an ectopic fat pad which also rescued the fertility in both sexes. However, pups born to rescued LD mothers died shortly after birth. We therefore examined the mammary glands of these mothers. MGs from LD mice were rudimentary and lacked terminal end buds. Leptin-injected and MEF rescued LD mice were able to become pregnant, showed normal pregnancy-associated glandular proliferation despite a smaller glandular area, were able to produce a small amount of milk that had grossly normal content of milk proteins and neutral lipids, but could not sustain pups to weaning. In order to separate the individual requirements for 1) adipokines such as leptin, 2) estradiol, and 3) epithelial-adipocyte interactions, we performed a series of experiments with both LD and ob (leptin-deficient) mice that received either estradiol or preadipocyte transplant. The resulting fat pad did not rescue the defect in MG development in LD mice. The defect also was not rescued with estradiol pellets. Ob/ob mice, like LD mice, lack leptin and estradiol, but retain adipose tissue. Ob mice have defective MG development. However, in striking contrast to LD mice, reconstitution of a WT fat pad in ob mice rescued the defect in MG development. Estradiol treatment did not rescue MG development in ob mice. Therefore direct interaction between mammary gland epithelia and adipocytes is a requirement for full invasion and expansion of the gland during puberty, but is not required for glandular proliferation during pregnancy and milk production. Given that excess adipose tissue is a risk factor for breast cancer we wanted to determine if breast cancer was affected by the absence of adipose tissue. LD mice were bred to MMTV-PyMT mice that develop spontaneous breast cancer. Remarkably, LD PyMT+ mice had accelerated growth of primary tumors compared to WT PyMT+ mice. Using our MEF transplant model future studies will be directed to understanding whether the accelerated breast cancer growth is due to loss of adipokines or altered epithelial-stromal interactions.