Investigating the complex interplay between genotype and high-fat-diet feeding in the lactating mammary gland using the Tph1 and Ldlr knockout models

Authors: CHENG, ADRIENNE - University Of Wisconsin; Li, Wenli; WALKER, TERESA - University Of Wisconsin; SILVER, CAYLEE - University Of Wisconsin; ARDENDT, LISA - University Of Wisconsin; HERNANDEZ, LAURA - University Of Wisconsin

Submitted to: American Journal of Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2020
Publication Date: 3/1/2021
Citation: Cheng, A., Li, W., Walker, T., Silver, C., Ardendt, L., Hernandez, L. 2021. Investigating the complex interplay between genotype and high-fat-diet feeding in the lactating mammary gland using the Tph1 and Ldlr knockout models. American Journal of Physiology. 320(3):E438-E452. https://doi.org/10.1152/ajpendo.00456.2020.
DOI: https://doi.org/10.1152/ajpendo.00456.2020

Interpretive Summary: Women who are obese have difficulty initiating and sustaining lactation. Currently, the impact of genetics and diet on breastfeeding outcomes is severely understudied. Here we explore the effect of diet and genotype on early and peak lactation in the mouse mammary gland. The low-density lipoprotein receptor knock-out (Ldlr-KO) transgenic mouse has been established as an obesity and hypercholesterolemia model. Additionally, the tryptophan hydroxylase 1 knock-out (Tph1-KO) mouse has recently been identified as a potential anti-obesogenic model. We created a novel transgenic mouse line by combining the Ldlr and Tph1 mouse lines (double knockout; DKO) to study the interaction between the two genotypes. Specifically, we aimed to investigate if the addition of Tph1-KO could ameliorate the negative effects of obesity in Ldlr-KO mice. Mouse mammary gland tissues were collected at early (lactation day 3/L3) and peak lactations (lactation day 11/L11). Mice were randomly fed either a high-fat diet or a low-fat diet. Whole transcriptome sequencing was used to investigate the global gene expression profiles and the underlying biological pathway enrichment of differentially expressed genes amongst different diets and genotypes. Our results indicated that diet played a larger role at L3, while genotype played a more significant role at L11. Thus, the impact of diet and genotype on lactation differ depending on stage of lactation, illustrating the complexities of understanding the intersection of these three parameters.

Technical Abstract: Obesity is a prevailing problem across the globe. Women who are obese have dif'culty initiating and sustaining lactation. However, the impact of genetics and diet on breastfeeding outcomes is understudied. Here we explore the effect of diet and genotype on lactation. We utilized the low-density lipoprotein receptor (Ldlr-KO) transgenic mouse model as an obesity and hypercholesterolemia model. Additionally, we used the tryptophan hydroxylase 1 (Tph1-KO) mouse, recently identi'ed as a potential anti-obesogenic model, to investigate if addition of Tph1-KO could ameliorate negative effects of obesity in Ldlr-KO mice. We created a novel transgenic mouse line by combining the Ldlr and Tph1 [double knockout (DKO)] mice to study the interaction between the two genotypes. Female mice were fed a low-fat diet (LFD; 10% fat) or high-fat diet (HFD; 60% fat) from 3 wk of age through early [lactation day 3 (L3)] or peak lactation [lactation day 11 (L11)]. After 4 wk of consuming either LFD or HFD, female mice were bred. On L2 and L10, dams were milked to investigate the effect of diet and genotype on milk composition. Dams were euthanized on L3 or L11. There was no impact of diet or genotype on milk protein or triglycerides (TGs) on L2; however, by L10, Ldlr-KO and DKO dams had increased TG levels in milk. RNA-sequencing of L11 mammary glands demonstrated Ldlr-KO dams fed HFD displayed enrichment of genes involved in immune system pathways. Interestingly, the DKO may alter vesicle budding and biogenesis during lactation. We also quanti'ed macrophages by immunostaining for F4/80 cells at L3 and L11. Diet played a signi'cant role on L3 (P = 0.013), but genotype played a role at L11 (P < 0.0001) on numbers of F4/80 cells. Thus the impact of diet and genotype on lactation differs depending on stage of lactation, illustrating complexities of understanding the intersection of these parameters.