RNA Sequencing of the Human Milk Fat Layer Transcriptome Reveals Distinct Gene Expression Profiles at Three Stages of Lactation

Abstract

Aware of the important benefits of human milk, most U.S. women initiate breastfeeding but difficulties with milk supply lead some to quit earlier than intended. Yet, the contribution of maternal physiology to lactation difficulties remains poorly understood. Human milk fat globules, by enveloping cell contents during their secretion into milk, are a rich source of mammary cell RNA. Here, we pair this non-invasive mRNA source with RNA-sequencing to probe the milk fat layer transcriptome during three stages of lactation: colostral, transitional, and mature milk production. The resulting transcriptomes paint an exquisite portrait of human lactation. The resulting transcriptional profiles cluster not by postpartum day, but by milk Na:K ratio, indicating that women sampled during similar postpartum time frames could be at markedly different stages of gene expression. Each stage of lactation is characterized by a dynamic range (105-fold) in transcript abundances not previously observed with microarray technology. We discovered that transcripts for isoferritins and cathepsins are strikingly abundant during colostrum production, highlighting the potential importance of these proteins for neonatal health. Two transcripts, encoding β-casein (CSN2) and α-lactalbumin (LALBA), make up 45% of the total pool of mRNA in mature lactation. Genes significantly expressed across all stages of lactation are associated with making, modifying, transporting, and packaging milk proteins. Stage-specific transcripts are associated with immune defense during the colostral stage, up-regulation of the machinery needed for milk protein synthesis during the transitional stage, and the production of lipids during mature lactation. We observed strong modulation of key genes involved in lactose synthesis and insulin signaling. In particular, protein tyrosine phosphatase, receptor type, F (PTPRF) may serve as a biomarker linking insulin resistance with insufficient milk supply. This study provides the methodology and reference data set to enable future targeted research on the physiological contributors of sub-optimal lactation in humans.

Prevalence and Risk Factors for Early, Undesired Weaning Attributed to Lactation Dysfunction

“…or obese. 13,14,18 Overweight BMI has also been associated with differences in prolactin response to suckling, 17 and insulin resistance is associated with both low milk supply and differences in the milk fat layer transcriptome, 19 suggesting that biological as well as sociocultural factors may affect breastfeeding success among overweight women. We also found higher rates of perceived lactation dysfunction among women with postpartum-depression symptoms.…”

“…[13][14][15][16] Obesity and insulin resistance are associated with differences in prolactin levels, 17 onset of lactogensis, 18 and the human milk fat layer transcriptome. 19 In addition, in animal models, obesity is associated with poor milk production. 20 With respect to depression and lactation, women with symptoms of depression and anxiety had lower oxytocin levels during feeding in a recent study, 21 and several other neuroendocrine mechanisms may link maternal mood disorders with breastfeeding difficulties.…”

Biosynthesis of milk fat, protein, and lactose: roles of transcriptional and posttranscriptional regulation

“…In fact, insulin upregulates the expression of yϩ transport system for cationic AA, such as Lys and Arg, in mouse mammary cells (200). In a recent study carried out by RNA sequencing of milk fat layer during colostrogenesis, transition, and mature milk in two groups of women based on lactation capability, it was proposed that protein tyrosine phosphatase receptor type F (PTPRF) might be responsible for mammary insulin resistance, resulting in decreased milk yield and poor lactation (121). The study did not consider if the expression of PTPRF had any relationship with milk protein synthesis.…”

“…The use of large transcriptomic analysis (i.e., microarray or RNA sequencing) by which to study the adaptation of mammary gland to lactation and/or change in milk production under specific conditions has been carried out in mouse (4,54,122,123,143,189,191,217,236,256), rat (3,47,187), bovine (31,36,56,75,96,144,183,209,218,233,239), sheep (209), goat (71,163,164), human (121,139,147), pig (204), kangaroo (120), and seal (144). It is beyond the scope of the current review to present a thorough discussion of the results from those studies.…”

Plasma amylin concentration in suckling goat neonates and its relationship with C-reactive protein, selected biochemical and hormonal indicators

“…The present results provide the first evidence that amylin concentrations correlate with insulin concentrations in female goat neonates. Lemay et al (2013) reported that insulin has an important role in breast milk synthesis and that there is a link between insulin resistance and insufficient milk supply through the tyrosine phosphatase, receptor type, F (PTPRF) gene. The relationship between amylin and insulin concentrations in female goat neonates suggests that amylin may also be related to milk yield in later years.…”