Effects of Trimethylamine N-Oxide on Mouse Embryonic Stem Cell Properties
Barron, Catherine Mary
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Trimethylamine N-oxide (TMAO) is a metabolite derived from dietary choline, betaine, and carnitine via intestinal microbiota metabolism. In several recent studies, TMAO has been shown to directly induce inflammation and reactive oxygen species (ROS) generation in numerous cell types, resulting in cell dysfunction. However, whether TMAO will impact stem cell properties remains unknown. This project aims to explore the potential impact of TMAO on mouse embryonic stem cells (mESCs), which serve as an in vitro model of the early embryo and of other potent stem cell types. Briefly, mESCs were cultured in the absence (0mM) or presence of TMAO under two different sets of treatment conditions: long-term (21 days), low-dose (20µM, 200µM, and 1000µM) treatment or short-term (5 days), high-dose (5mM, 10mM, 15mM) treatment. Under these treatment conditions, mESC viability, proliferation, and stemness were analyzed. mESC properties were not negatively impacted under long-term, low-dose TMAO treatment; however, short-term, high-dose treatment resulted in significant reduction of mESC viability and proliferation. Additionally, mESC stemness was significantly reduced when high-dose treatment was extended to 21 days. To investigate an underlying cause for TMAO-induced loss in mESC stemness, metabolic activity of the mESCs under short-term, high-dose TMAO treatment was measured with a Seahorse XFe96 Analyzer. TMAO treatment significantly decreased the rate of glycolysis, and it increased the rate of compensatory glycolysis upon inhibition of oxidative phosphorylation (OxPHOS). It also significantly increased the rate of OxPHOS, maximal respiratory capacity, and respiratory reserve. These findings indicate that TMAO induced a metabolic switch of mESCs from high glycolytic activity to greater OxPHOS activity to promote mESC differentiation. Additionally, TMAO resulted in increased proton leak, indicating increased oxidative stress, and elucidating a potential underlying mechanism for TMAO-induced loss in mESC stemness. Altogether, these findings indicate that TMAO decreases stem cell potency potentially via modulation of metabolic activity.
General Audience Abstract
Trimethylamine N-oxide (TMAO) is a metabolite that is produced by the bacteria in the gut after the consumption of specific dietary ingredients (e.g., choline, carnitine, betaine). These ingredients are commonly found in meat and dairy products, and thus make up a large part of the average American diet. Recently, it was discovered that high TMAO levels in the bloodstream put people at an increased risk for heart disease, neurodegenerative diseases (e.g., Alzheimer's Disease), diabetes, stroke, and chronic kidney disease. At the cellular level, there is evidence that TMAO increases inflammation and the production of oxygen radicals, which causes cells to lose their function and promotes the onset of disease. TMAO has been well studied in adult cell types; however, no one has investigated whether TMAO will impact cells of the early embryo. This project aims to explore the impact of TMAO on mouse embryonic stem cells (mESCs), which are cells that represent the early stage of embryonic development and are critical for proper development of the final offspring. In addition, mESCs may also help to provide insight into how TMAO impacts other stem cell types, some of which are present throughout the entire human lifespan and play an important role in the body's ability to repair itself and maintain overall health. My project demonstrated that TMAO does not impact the overall health of mESCs under normal conditions, which signifies that TMAO generated by a pregnant mother may not directly impact the early embryonic stage of development. Further studies should be conducted to determine the potential impact of TMAO on late stages of embryonic and fetal development. Next, to simulate diseased conditions, the mESCs were treated with extremely high concentrations of TMAO in order to determine what concentration of TMAO will negatively impact these cells. It was found that at 5mM TMAO, mESCs begin to lose their basic properties and become dysfunctional. They are impaired in their viability, growth, ability to become other cell types, and in their metabolic activity. These mESC properties are shared with several types of adult stem cells, and therefore, these findings help to provide insight into how TMAO may impact stem cells found in the adult body which are exposed to a lifetime of high TMAO levels. In the future, we would like to further explore the impact of TMAO on mESCs at the molecular level as well as examine the direct impact of TMAO on other stem cell types.
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