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ARS Home Pacific West Area Davis, California Western Human Nutrition Research Center Obesity and Metabolism Research Research





- Bennett, Brian

Research Project: **Location:
                            Obesity and Metabolism Research** Project Number: 2032-51530-025-044-I
                        
                        Project Type: Interagency Reimbursable Agreement Start Date: Apr 1, 2020
                        
                        End Date: Mar 31, 2025 **Objective:**
                        
                        Recent studies have highlighted the role of the intestinal microbiome or microbiota in the susceptibility to a number of diseases including metabolic syndrome. The microbiota is composed of millions of bacteria that can have profound effects on nutrient availability while at the same time producing a number of disease related metabolites, such as our previous studies of trimethylamine (TMA) and trimethylamine N-oxide (TMAO). Many questions remain regarding the contribution of the microbiome to the metabolic syndrome; for example we do not know which bacteria in the gut are regulating metabolic syndrome susceptibility and how diet interacts with these bacteria. Moreover the increasing prevalence of early onset diabetes and childhood obesity suggest that maternal factors may be modulating disease risk. We suggest that discovery of which bacteria, and their gene expression, interact with altered dietary intake are critical to refine our dietary recommendations. 

Our preliminary studies suggest that maternal diet may be interacting with the microbiota to affect metabolic syndrome. In the proposed work, we capitalize upon our expertise in mouse genetics to further understand the impact of maternal diet on metabolic syndrome susceptibility in offspring. These studies allow us to leverage the well-controlled studies in mice using the most advanced mouse genetic resources available called the Collaborative Cross. Using a simple breeding scheme we will test the effects of diet on maternal microbiota, the transmission of microbiota to offspring and the effects of these transmitted microbiota on Metabolic Syndrome. Specific bacterial genes are identified through RNA-Seq analysis and tested in vivo using adoptive transfer experiments.
Our specific objectives at this time are as follows:

Objective 1: Determine the trans-generational genetic regulation of effects of perturbed maternal diet on microbiota composition and susceptibility to metabolic syndrome. Both genetics and environmental factors, such as diet, have profound effects on disease susceptibility. We hypothesize that the effects of maternal diet on the microbiota are in part affected by maternal genetics and test this using a diallel design. 
Objective 2: Identify perturbations in microbiota gene expression in response to altered maternal diet and their relationship to metabolic syndrome. We hypothesize that transgenerational effects are mediated, in part, by altered microbial gene expression. **Approach:**
                        
                        Preliminary data suggests that maternal diet can mediate metabolic syndrome risk. Understanding the relationships between maternal diet, microbiota perturbations and MetSyn risk can help our understanding of this rapidly developing epidemic. As this phenotype is not effectively testable in humans, we propose to use mouse studies to accomplish our aim. To identify potential genetic interactions, we are using CC-RIX mice because this question cannot be answered using a single inbred strain of mice such as the commonly used C57BL/6J mouse. 

Study Design: This study will consist of reciprocal crosses of Collaborative Cross mouse strains. Collaborative Cross strains will be selected for this study based on several parameters including adiposity, breeding performance and genetic diversity. Reciprocal crosses of these strains will be performed where males from 1 CC line are mated with females from line 2. This cross is repeated with the sex reversed as compared with the original cross, and tests the role of maternal genotype on the inheritance of specific molecular and clinical traits. It is important to note that the progeny of reciprocal crosses of 2 specific CC lines are essentially genetically identical at the autosomes. They vary genetically only in their Y chromosomes (in males) and mitochondrial DNA. Thus, this is an ideal design to study non-genetic maternal effects on the offspring. Studies such as these are not feasible in humans.
Objective 2 will first identify bacterial genes highly associated with increased MetSyn susceptibility by RNA-seq. Both the taxa associated with MetSyn (from Objective 1) and the candidate genes identified by RNA-seq are then tested using several methods. The overall goal of these studies is to first validate microbial candidates and their gene expression.

We will next perform Microbial Transplants to test transmission of the maternal diet effect. The next experiment we propose is designed to test if the maternal microbiota affects MetSyn risk using adoptive transfer experiments (MT), as previously described. Two CC-RIX mouse strains divergent for MetSyn risk [hereafter referred to as strain 1 (susceptible) and 2 (resistant)] will be selected based on the analyses in Aim 1. We use two strains divergent for MetSyn risk to more effectively test both potentially protective and deleterious microbiota. We anticipate that the protective effects of maternal microbiota will be more easily observed in a susceptible CC-RIX strain, and conversely, deleterious effects may be more apparent in a CC-RIX strain that is resistant to MetSyn.


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