Nutritionally Driven Sporadic Intestinal Tumors: Impact on Stem Cells

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Western-style diets are strongly linked to human sporadic colorectal cancer (CRC), the predominant subtype of all human CRCs. This can be recapitulated in the mouse fed a purified rodent diet (NWD1) mimicking intake of major human nutrient risk factors for CRC. Our extensive published work on this model has established that there are fundamental biochemical and molecular field effects in the histologically normal appearing mucosa of NWD1 fed mice, long before sporadic tumors develop. This includes altered epithelial cell maturation, expanded and elevated Wnt signaling throughout the mucosa, and altered energy metabolism. More recently, we reported that feeding NWD1 has profound effects on ability of Lgr5hi crypt base columnar cells to function as stem cells in intestinal homeostasis and in tumor development. Data submitted for publication (presented herein), establish that feeding NWD1 differentially programs Lgr5hi and Bmi1creERT2 marked intestinal stem cells (RNAseq analysis). In Lgr5hi cells, this significantly elevates expression of DNA damage response (DDR) genes, in particular in the mismatch repair pathway, suppresses accumulation of Lgr5hi cell somatic mutations, and alters mutational spectra and signature. Further, consistent with the shift we reported in relative utilization of carbohydrate and fat as energy sources in mice fed NWD1, there was reduced expression in Lgr5hi cells of genes encoding components of the TCA cycle and of multiple subunits for each of the 5 complexes of mitochondrial electron transport, and for Pgc1a, a master regulator of mitochondrial function and biogenesis. As a consequence, NWD1 reduced Lg5hi cell function in intestinal homeostasis and tumorigenesis, but increased ability of Bmi1 progeny to act as stem-like cells in homeostasis and tumor development. Therefore, NWD1 - highly relevant to human nutritional exposures strongly linked to population risk for CRC – had a major impact on sculpting the contribution of different intestinal stem cell populations to contribute to mucosal homeostasis and tumorigenesis. These dietary effects on adult stem cells are potentially paradigm shifting in terms of understanding risk for sporadic tumors. Our overall hypothesis is that these changes in long-lived stem cells provide new approaches for early evaluation and modulation of relative risk. Aim 1 identifies the evolution with time of epigenetic and genetic alterations by which NWD1 alters mouse intestinal/colonic adult stem cells in elevating probability for sporadic CRC, and the relative stability of such changes once established when the diet is altered. Aim 2 determines the impact of NWD1 on altered DNA damage response to promoting tumorigenesis from the different stem cell populations. Aim 3 determines the extent to which genetic inactivation of Pgc1a targeted to Lgr5 stem cells of the intestinal and colonic mucosa is sufficient to recapitulate the effects of NWD1 on alteration of Lgr5 stem cell programming and contribution of Lgr5 cells to intestinal homeostasis and tumorigenesis.