Aims: To describe tDRs in human milk EVs and their associations with maternal body mass index, age, dietary indices, breastfeeding frequency, season and time of milk collection in a Latina population.
Materials & methods: We sequenced small RNAs from EVs from 109 mature human milk samples collected at 1 month after delivery in the Southern California Mother's Milk Study. We grouped tDRs using hierarchical clustering and clusters were compared across tDR characteristics. We analyzed associations of tDRs with intrinsic maternal variables (body mass index, age), maternal nutrition (caloric intake, Healthy Eating Index, Dietary Inflammatory Index), and variables related to feeding and milk collection (breastfeeding frequency, season and time of milk collection) using negative binomial models.
Results: We identified 338 tDRs expressed in 90% or more of milk EV samples, of which 113 were identified in all samples. tDR-1:26-Gly-CCC-1-M4 accounted for most reads (79%). Pathway analysis revealed a wide array of biological processes and disease mechanisms across the four tDR clusters. tDRs were associated with season of collection, time of collection, breastfeeding frequency, and the dietary inflammatory index.
Conclusions: tDRs are abundant in milk EVs and may be sensitive to maternal diet, seasonality, time of day, and breastfeeding frequency.
Keywords: Biomarkers; epigenetics; human milk; nutrition; tRNA.
Human milk contains important nutrients and molecules that help to protect the infant from disease and ensure proper development. Small pieces of RNA that originate from transfer RNA molecules are enriched in human milk, particularly in compartments that exist outside of the cell and can be easily move from cell to cell. These small RNAs – referred to as tRNA-derived RNAs (or tDRs) – have gene silencing functions which may implicate them in health and development. Additionally, small RNAs like tDRs can survive digestion by the infant’s stomach when encapsulated in these extracellular compartments, meaning that they can be fully transferred from mom to baby. However, tDRs have not yet been characterized in human milk. In this study, we measured tDRs in mature milk samples from a cohort of mothers. We characterized these tDRs and tested their associations with several maternal characteristics, dietary variables, and variables related to milk collection and breastfeeding. We found that tDRs were readily identifiable and were associated with several tested variables, including maternal diet, seasonality, time of day, and breastfeeding frequency.