Date of Award
8-13-2024
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Undernutrition is a serious global health challenge; it accounts for nearly half of all mortality for children under the age of 5. Worse, undernutrition is compounded by intergenerational inheritance and can be transmitted from mother to offspring. The burden of undernutrition is unequally distributed around the world, with South Asia and Sub-Saharan Africa accounting for almost 60% of the global childhood stunting. Undernutrition is detrimental to many aspects of development, including long-term deficits in neurodevelopment, and current interventions rarely ameliorate long-term cognitive and motor deficits. Therefore, other causes of undernutrition need to be elucidated in order to treat this epidemic and reduce deficits to brain development. Previous research demonstrated a causal relationship of the gut microbiota on undernutrition. However, there remain many questions about how the microbiota of healthy or undernourished children impacts brain development. Severe acute malnutrition (SAM) is a form of undernutrition that is defined as individuals who are three or more standard deviations below an age-matched healthy reference cohort. To better understand how the gut microbiota may impact neurodevelopment, we developed a pre-clinical model of gnotobiotic mice colonized with intact fecal microbiota from Bangladeshi children with healthy growth phenotypes or SAM. This represented the first time these microbiota had been gavaged into mice with the intent to study brain development. Dams were colonized with these gavage mixtures and the microbiota was passively transferred from dams to pups. Microbial community composition in the cecum and gene expression in the hindbrain and cortex were analyzed from postnatal 14 (P14) offspring. However, genes were not consistently differentially expressed between replicate experiments, therefore another model of undernutrition, in which the microbiota was previously associated with changes in gene expression in the brain, was utilized for future experiments. Environmental enteric dysfunction (EED) is a reversible, subclinical inflammatory enteropathy of the small intestine (SI) that contributes to undernutrition. Previous research identified a core group of SI bacteria present in undernourished Bangladeshi children with biopsy-confirmed EED, whose abundances correlated with their degree of stunting and gut inflammation. Two culture collections were generated from duodenal aspirates from these children: a more diverse consortium of all isolated bacteria and a subset of representative species. Colonization of germ-free mice with the larger consortium induces an inflammatory response in their offspring. The inflammatory consortia also replicates many features of the intestinal dysbiosis found in humans. To explore dysfunction beyond the small intestine, snRNA-Seq of the cerebral cortex identified many cell lineages and pathways whose expression of metabolic and signaling was perturbed. Glutamatergic neurons, as well as astrocytes and oligodendrocytes had altered gene expression. Building on this work, my thesis aimed to elucidate the mechanisms by which the small intestinal microbiota of children with EED impacts neurodevelopment when transferred from mother to offspring. Here, I present novel gnotobiotic behavioral proof-of-concept experiments to quantify how the intergenerational transmission of two bacterial consortia impacts early perinatal neurodevelopment. My experiments additionally expanded on these analyses by comparing colonization of the consortia on both a diet mimicking those of an adult living in Dhaka, Bangladesh, but also breeder chow diet. Metagenome-assembled genomes (MAGs), previously generated, and shotgun sequencing of the abundances of cecal and fecal communities from dams demonstrated a stable colonization of these two consortia over the course of years. Differential abundance analyses of dams confirmed colonization of key inflammation-associated taxa identified in previous in EED gnotobiotic models. Both diet and microbial community impacted the colonization within the cecum of both dams and offspring. These findings expand on previous literature and provide the basis for further studies exploring both diet and the microbiota on EED. To investigate the impact of the microbiota and diet on the neurodevelopment of perinatal development, I developed assays for adapting behavioral experiments within a gnotobiotic isolator. One paradigm to elucidate the effects on muscle strength, coordination, and sensory processing, modified reflex development assays to fit within the gnotobiotic isolator. Reflexes are some of the earliest, unlearned behaviors that can be measured in mice. These experiments indicate that muscle strength is decreased in mice colonized with the inflammatory community or fed the human mouse chow. Additionally, experiments were conducted to measure how social communication is affected in these models. Ultrasonic vocalizations (USVs), which are emitted by pups to communicate distress and induce retrieval by the dams, were measured within the isolator. These experiments identified increased arousal in the pups colonized with the inflammatory compared to non-inflammatory consortia colonized pups. Additionally, diet impacted call rate, with pups reared by dams fed the Adult Mirpur diet emitting more calls than those fed breeder chow diet. These findings provide preclinical evidence that both the diet and microbial community cause motor and social communication deficits. In summary, this thesis illustrates an approach for elucidating the impact of both diet and the microbiota on neurodevelopment and muscle strength in preclinical models. Further exploration utilizing these models, and continuing them into adulthood or testing different diets, may expose important understandings of how to improve neurodevelopmental outcomes of children experiencing undernutrition and EED.
Language
English (en)
Chair and Committee
Jeffrey Gordon
Committee Members
Aaron DiAntonio; Daniel Goldberg; Jason Yi; Joseph Dougherty
Recommended Citation
Byrne, Alexandra Elizabeth, "Gnotobiotic Mouse Models For Characterizing the Role of the Microbiota On Undernutrition and Early Postnatal Brain Development" (2024). Arts & Sciences Electronic Theses and Dissertations. 3285.
https://openscholarship.wustl.edu/art_sci_etds/3285