Mammary cells synthesize insulin during lactation (622.3)

Abstract

The mammary gland undergoes extensive remodeling during pregnancy and lactation to mature into a milk‐secretory organ. This remodeling is accompanied by a series of alterations in gene expression that are fuelled by hormonal changes facilitating maturation of epithelial cells. Insulin, supplied by the maternal circulation, is thought to play a key role in this process. In this study, we examined whether mammary cells endogenously synthesize insulin during lactation. First, we stained rare specimens of human lactating breast tissue for insulin and found that some, but not all, mammary epithelial cells were positive for insulin. We subsequently confirmed this finding with FACS. We then detected the transcript for insulin in mammary cells accessed via freshly expressed breastmilk. Transcript levels were highly variable among the breastmilk samples tested, and were significantly higher than in mammary cells accessed from the resting breast (P<0.05). Insulin expression in breastmilk cells correlated with expression of various stem cell genes, such as ESRRB, and appeared to be associated with the stage of lactation. We have for the first time confirmed that the insulin in breastmilk is derived from both the pancreatic beta cells and mammary cells of the lactating epithelium. Furthermore, mammary‐derived insulin may provide developmental signals within the mammary gland as well as contribute to breastmilk insulin.