The benefits of human breast milk as a food for infants is frequently touted, but why it is so beneficial is not well understood.
Part of the answer may begin with short, single-stranded RNA molecules microRNAs--that fine-tune the activity of genes and their associated proteins to regulate metabolism and the immune system, said a consortium of researchers at Baylor College of Medicine, Agricultural Research Service/U.S. Department of Agriculture Children’s Nutrition Research Center at BCM and Texas Children’s Hospital and the University of Houston in a report that appears online in the open-access journal PLOS ONE.
"We wanted to know if the microRNAs in breast milk were the same as those found in the rest of the body or were they novel to breast milk," said Dr. Kjersti Aagaard, associate professor of obstetrics and gynecology at BCM and corresponding author of the report. "We began our work with the premise that these microRNAs survive the stomachs and intestinal tracts of the infant. We thought this might be one of the ways that mothers regulate what genes are turned on and off in infants who do not yet have a mature immune or metabolic system."
Zeroing in on fat layer
In older humans with a mature microbiome, the bacteria in the gut makes it possible to metabolize fats and sugars and make vitamins. Infants, however, lack those bacterial helpers. To study breast milk, Aagaard and her colleagues collaborated with Dr. Morey Haymond, professor of pediatrics - nutrition at BCM, and Dr. Preethi H. Gunaratne, an associate professor of biology and biochemistry at the University of Houston and assistant professor of pathology at BCM, to determine the genetic sequence of the microRNAs found in breast milk. After much study, they zeroed in on the fat layer of the milk.
Using a special technique, they isolated the microRNAs in the breast milk and then used a combination of genetic sequencing techniques combined with computing expertise to identify them. Some were the same as found in the rest of the body, but a few found in low abundance had never been discovered before.
To find out how diet affected these microRNAs, they fed breast-feeding mothers a variety of diets: high fat, high carbohydrate, high galactose (a sugar found in dairy products) and high glucose or sugar. The microRNAs responded only to the high fat diet, said Aagaard.
"The breast milk of the moms on a high fat diet had an increase in several of the microRNAs," said Aagaard.
She and her colleagues believe the breast milk may be altered through these microRNAs to enable infants to deal with the high fat diet eaten by their mothers that the babies are not yet able to accommodate, she said.
Role of microRNAs becoming clearer
"The whole role of microRNAs in affecting metabolic change in a variety of tissues is becoming clearer," said Haymond, who is also director of the metabolic research unit at the CNRC and program director of the Clinical Scientist Training Program at BCM. "The fact that we have identified these unique microRNAs in breast milk means that, perhaps, through evolution, they are specific to particular roles in the gut or metabolism of the newborn."
Haymond credited the nursing mothers who took part in this research and other projects that are directed at understanding the make-up of breast milk and how women produce it.
Others who took part in this work include Erika M. Munch, R. Alan Harris, Mahmoud Mohammad, Sasha M. Pejerrey, Lori Showalter, Min Hu, Cynthia D. Shope and Patricia D. Maningat, all of BCM and Ashley L. Benham of the University of Houston.
Funding for this work came from the National Institutes of Health (1R01DK089201-01A1), the NIH new innovator pioneer award and the U.S. Food and Drug Administration.