Lactation explanation

MIT researchers have performed a large-scale, high-resolution study that shows how mammary gland cells change over time in nursing mothers, a task that has been difficult because the tissue can’t be biopsied during lactation. The findings could eventually yield new ways to boost milk production or improve the composition of infant formula, perhaps optimizing it for different stages of infancy.

To gather the necessary information noninvasively, the researchers isolated breast cells from the milk itself and analyzed them using single-­cell RNA sequencing, which can determine which genes are being expressed in a cell at a given moment. After studying 50 milk samples provided by 15 mothers between three days and nearly two years after childbirth, the researchers were able to identify a variety of changes in gene expression, some linked to factors such as hormone levels, illness of the mother or baby, the mother starting birth control, and the baby starting day care.

“We showed that milk does change over the entire course of lactation, even after years of milk production,” says senior author and former postdoc Brittany Goods, PhD ’17, an assistant professor of engineering at Dartmouth.

The most-abundant cells they found were lactocytes, which expressed many genes for proteins found in breast milk as well as transporters needed to secrete proteins, micronutrients, fat, and other components. As time went on, the researchers found, the proportion of lactocytes involved in milk production went down, while the proportion involved in structural support of the mammary gland went up. At the same time, genes involved in responding to the hormone prolactin became more active in the milk-­producing lactocytes but dropped off in structural ones. These changes may be related to the changing nutritional needs of infants as they grow.

The study “paves the way for mapping out and better understanding some of the pathways that these cells use to accomplish the tremendous amount of work that they do,” Goods says.

“It not only gives us a way to understand lactation, but it also gives us a set of data and tools to be able to engineer better solutions to improve the quality of life of mothers.”