Novel Nutrient Functions and Sensing Mechanisms

Project Summary In our original proposal for the R35 grant application, we described the two major goals of the research in the field of nutrient function and sensing. One is to discover nutrient value, or the benefits, of specific bacteria-produced metabolites on human physiology, which had been predicted by the symbiotic

relationship between commensal microbes and host animals. The second goal was to uncover novel mechanisms that regulate specific physiological events in response to deficiency of specific nutrients that include fatty acids, nucleotides, and amino acids. These studies address fundamental questions that are

closely related to human health. For this "Supplement Application" that aims to acquire funding for purchasing a piece of equipment to measure oxidative respiration in animal cells, the research strategy mainly focuses on the first goal. Using innovative genetic screens in the nematode C. elegans, we have

identified unexpected beneficial roles of certain bacterial metabolites, including the siderophore enterobactin and bacterial cell wall components peptidoglycan muropeptides, on animal development and behaviors. Supported by the R35 grant and its R01 precursor grant, we have made exciting progress in understanding

the mechanisms underlying these novel functions. Both molecules enter the mitochondria of host intestinal cells, bind to ATP synthase, and promote basic mitochondrial functions. In the case of muropeptides, we have found that beneficial molecules are disaccharide muropeptides containing a short AA chain, and they

enter mitochondria of intestinal cells to repress oxidative stress. Strikingly, muropeptides execute this role by binding to multiple subunits of ATP synthase, which consequently stabilizes the complex and promotes its activity. This finding defined the first agonist of the ATP synthase. More recent studies using cultured

human intestinal epithelial cells, fibroblasts from a disease patient, and mice treated with antibiotics have clearly indicated the roles of muropeptides in promoting oxidative phosphorylation and suppressing oxidative stress in mammalian cells. In the next several years, we will continue to expand the analyses on

potent muropeptides to understand its structural property, its role in promoting oxidative phosphorylation in different mammalian tissues, and its potential effect in suppressing mitochondrial dysfunction in disease cells and mice. Such studies are of high medical significance, as mitochondrial dysfunction is well known to

be associated with a broad range of human diseases including major neurodegenerative, cardiovascular, and metabolic diseases. We also plan to explore potential roles of other metabolites and nutrient sensing mechanisms in mitochondrial homeostasis. Having a Seahorse Analyzer to examine oxidative respiration

would greatly facilitate these proposed studies on mitochondrial functions.