Diverse and active roles for adipocytes during mammary gland growth and function

Abstract

The mammary gland is unique in its requirement to develop in close association with a depot of adipose tissue that is commonly referred to as the mammary fat pad. As discussed throughout this issue, the mammary fat pad represents a complex stromal microenvironment that includes a variety of cell types. In this article we focus on adipocytes as local regulators of epithelial cell growth and their function during lactation. Several important considerations arise from such a discussion. There is a clear and close interrelationship between different stromal tissue types within the mammary fat pad and its adipocytes. Furthermore, these relationships are both stage- and species-dependent, although many questions remain unanswered regarding their roles in these different states. Several lines of evidence also suggest that adipocytes within the mammary fat pad may function differently from those in other fat depots. Finally, past and future technologies present a variety of opportunities to model these complexities in order to more precisely delineate the many potential functions of adipocytes within the mammary glands. A thorough understanding of the role for this cell type in the mammary glands could present numerous opportunities to modify both breast cancer risk and lactation performance.

Fig. 1

Diverse relationships between adipose tissue and the mammary epithelium. a and b) Photomicrographs of epithelial ducts within the #3 thoracic mammary glands from the same pubescent female Balb/C mouse at 55 d of age invested within a) unilocular, white adipose tissue and b) multilocular, brown adipose tissue. Both adipose tissue types are associated with the thoracic mammary glands in mice. Hematoxylin and eosin. c) Epithelial ducts growing within the mammary fat pad of a nulliparous female pig, invested within collagenous intralobular stroma beyond which lies unilocular white adipose tissue. d) Regressing alveoli within the mammary gland of a post-lactational sow showing interspersed, lipid-filled adipocytes. Magnification is same for all panels, scale bar in panel A is 50 um