Location: Children's Nutrition Research Center
Project Number: 3092-51000-062-003-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Apr 1, 2019
End Date: Mar 31, 2024
Objective 1: Select inbred mouse strains with phenotypic extremes in milk production will be used to: a) identify genomic variants along with intestinal and mammary-expressed genes that differentiate low and high milk production, and b) determine the extent to which genome-driven differences in milk production and mammary gene expression are directly mediated through host-dependent differences in the intestinal and/or mammary tissue microbiome. Subobjective 1A: Sequence the genomes of additional unsequenced strains from our original milk yield cohort and then use this completed lactation phenome genotype data to identify strain-specific private alleles and predict the functional consequences of these variants on genes with the potential to regulate traits defined in the lactation phenome dataset. Subobjective 1B: Combine the lactation phenome dataset with the expanded common variant data from sub objective 1A to conduct an enhanced joint-GWAS of SNP, INDEL, and SV, and to subsequently predict the functional consequences of the newly identified variants to lactation. Subobjective 1C: Using a complete 3x3 diallele cross of QSi3, QSi5, and PL/J determine the contribution of strain-dosage, heterosis, parent-of-origin, and epistasis to milk production and composition, and mammary gland development during early lactation, and identify mammary epithelial cell and intestinal eGenes on the basis of allelic imbalance. Subobjective 1D: Integrate the set of eGenes discovered in 1C with the set of private and common variants discovered 1A and1B and employ network modeling to predict and test those variant-eGene pairs that are most likely to cause the variation in the lactation phenome traits. Subobjective 1E: Analyze the fecal microbiota along with prolactin and oxytocin in samples obtained from the diallel conducted under sub-objective 1C to determine the contribution of strain-dosage, heterosis, parent-of-origin, and epistasis to the diversity and richness of the intestinal microbiota, to the abundance of specific taxa, and to neuroendocrine function in mouse strains with a genetic propensity for high or low milk yield. Objective 2: Determine the short and long-term impact of lactation on the maternal hepatic metabolome composition and hepatic signaling pathways in mice. Objective 3: Determine the impact of maternal nuclear receptor signaling on the maternal hepatic metabolome and pup viability.
Genetic background is known to influence variation in milk production however environmental factors also play a role. Advances in high-throughput DNA sequencing technologies have revolutionized the way in which the microbial world is viewed and has led to the concept that the microbiome is a major regulator of normal development and health. The microbiome is regulated by diet, but is also under the control of the host genome. In this regard, the full number of host genetic variants associated with lactation-related traits remains to be determined. Differences in milk production are driven by changes in gene expression within organs important to milk synthesis. Additionally, the intestinal microbiome is controlled by the host genome, but can directly influence gene expression within the host. We aim to understand how variations in the maternal genome interact with the microbiome to determine lactation success. Whole genome sequence data from select mouse strains will be used to identify genetic variants that are unique to high or low milk production. These newly identified variants will be functionally linked to milk production and composition, and to lactation-induced intestinal and mammary gene expression through a specific RNA Sequencing test known as allelic imbalance. Strain- and allele-dependent differences in fecal ribosomal 16s sequencing reads will associate the variants with the intestinal microbiome. Lastly, maternal microbiome seeding through neonatal cross-fostering will establish the ability of the intestinal microbiome to over-ride the effects of genetic background lactation-dependent gene expression and milk production. Additionally, although rates of breastfeeding (BF) have increased, there is much variability in BF initiation and duration rates. Lactation insufficiency, inability to produce enough breast milk to support offspring development, is estimated to be between 40-60%. The underlying mechanisms of lactation insufficiency are not well understood and require more study. The liver and small intestine undergo metabolic changes that support the production of mature milk in the mammary gland in lactating rodents, including significant increases in hepatic and intestinal bile acids. In lactating animal models, key enzymes involved in cholesterol and lipid homeostasis are altered during lactation. Bile acids promote the solubilization of cholesterol and lipid soluble nutrients, which enhance milk lipid nutrient composition. These genes are regulated by a group of transcription factors called nuclear receptors- the metabolic nuclear receptors farnesoid x receptor (FXR) and peroxisome proliferator activated receptor alpha (PPARalpha). These nuclear receptors and their target genes represent novel targets for study to address our central hypothesis that manipulation of hepatic and intestinal nuclear receptors alters lipid composition in breast milk. The overall goal of this project is to determine the role of FXR and PPARalpha in the metabolic adaptations of the maternal liver-gut axis.