New research suggests that microscopic projections of cells called villi in the small intestine increase in size during pregnancy and breastfeeding. Examples of these villi are shown in the image above. (Image credit: © IMBA/Onji_Kulcsar)
During pregnancy, breasts enlarge, resting heart rate increases, and organs shift to make room for the developing fetus. Now, scientists have added another aspect to the list: the intestines get significantly bigger.
The lining of the small intestine, known as the epithelium, changes its structure and doubles in size during both pregnancy and breastfeeding, according to a new study in mice and 3D human tissue models.
During these critical stages of reproduction, mothers must consume more nutrients to support their baby’s growth and development. The team behind the study hypothesizes that these gut changes may also help mothers absorb more nutrients from food, allowing them to pass on even more to their baby. However, this hypothesis has not yet been confirmed.
The scientists outlined their new findings in a paper published December 4 in the journal Nature.
“Our team has discovered a remarkable new way in which mothers' bodies adapt to ensure the health of their babies,” said study co-author Josef Penninger, scientific director of the Helmholtz Centre for Infection Research in Germany.
The team made the discovery while studying the role of a signaling molecule known as RANK, which is present in many tissues throughout the body. The molecule had previously been shown to regulate the formation of mammary glands, which are responsible for milk production. Hormones associated with reproduction, such as progesterone, also increase RANK production in these glands, suggesting that the molecule helps orchestrate the changes in the body associated with pregnancy.
In addition to mammary tissue, RANK is also found in intestinal epithelium, but very little has been known about its function in this area.
In the new study, Penninger and his colleagues used stem cells to create small 3D replicas of both human and mouse small intestines. These “organoids” were engineered using specialized chemicals. The cells inside the mini-intestines were then exposed to RANK, which caused a series of structural changes.
Specifically, tiny, finger-like projections protruding from epithelial cells suddenly lengthened and flattened. These projections, known as villi, increase the surface area of the intestine, thereby improving the absorption of nutrients through the tissue.
The team found that similar changes occurred in pregnant and lactating mice. However, without RANK, these changes did not occur. In separate experiments where they genetically modified mice so that they did not produce RANK, the gut remained unchanged.
Moreover, milk produced by RANK-deficient mice was less nutrient-dense than milk from RANK-producing mice, and the mice produced underweight offspring.
Taken together, these results suggest that the intestinal epithelium changes during the reproductive process to maximize nutrient absorption by the developing baby, the team of researchers suggested.
“These new studies provide the first molecular and structural explanation for how and why the gut changes to meet maternal increased nutrient needs,” Penninger said.
The team next plans to investigate whether similar tissue remodeling occurs in humans, and whether factors other than RANK regulate this process.
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