Date of Award
Master of Science (MS)
Lisa J Bain
Arsenic is a natural toxicant commonly found in drinking water. Since its main route of exposure is oral, arsenic is continually in contact with the small intestine. While in vitro arsenic exposures of environmentally relevant concentrations can disrupt differentiation in cardiac and skeletal muscle, neurons, and keratinocytes, little is known of the impact of an in vivo arsenic exposure. Since the epithelium of the small intestine rapidly regenerates, we wanted to investigate whether arsenic alters the balance of renewal and differentiation. Small intestinal organoids (enteroids) were used to assess arsenic’s impact on intestinal homeostasis by exposure to 0, 1, and 5 μM iAs for 6 days. After collection, transcript and protein levels of markers identifying intestinal stem cells (ISCs) and differentiated epithelial cells were investigated. However, the arsenic-exposed and control samples showed no differences. Our lab has recently shown that an in vivo exposure of 100 ppb iAs reduced transcript levels of Lgr5, Atoh1, and Defa1. Because the in vivo and in vitro data were inconsistent and because previous studies showed that stromal cell signals are essential in regulating intestinal homeostasis, I hypothesized that arsenic may impair stromal cells and their secreted signals rather than targeting the intestinal epithelial cells directly.
Male C57BL/6 mice were exposed to 0 or 100 ppb sodium arsenite in drinking water for five weeks. The proximal 10 cm of the small intestine was then collected for further analysis. The results show that arsenic exposure altered intestinal morphology, indicated by a 37% reduction in the width of connective tissue underlying the crypt. Transcript levels of platelet derived growth factor alpha (Pdgfra), an important cellular marker of several stromal cell populations, were decreased by more than four-fold. Telocytes, a stromal cell important in cell-to-cell communication, are marked by high levels of Pdgfra. Arsenic exposure resulted in a decreased spread to telocyte projections in the villus tip. Transcripts of Bmp2 and Bmp4, signals important in promoting differentiation, were reduced by 32% and 36% in arsenic-exposed tissues, respectively. In addition, mRNA levels of Gremlin1 and Gremlin2, Bmp antagonists expressed in the stem cell niche, were reduced 50% and 60% when exposed to arsenic. These results suggest that the reduction in Pdgfra+ cells leads to a reduction in an expression of signals important in the Wnt and Bmp pathways - pathways important in maintaining the intestinal balance between stemness and differentiation.
Kellett, Michael, "Arsenic Exposure Decreases the Number and Signaling of Distinct Intestinal Stromal Cells" (2020). All Theses. 3388.