The colonic stem cell niche, located at the base of colonic crypts, drives the most rapidly self-renewing tissue in the body, the colonic epithelium. Gradients of extrinsic and intrinsic signals coordinate the proliferation of the niche, which is responsible for the rapid regeneration necessary for intestinal homeostasis. It is believed that disruptions of these signals along the crypt-axis lead to widespread proliferation and disordered epithelium, the hallmarks of colorectal cancer (CRC). Of great interest in intestinal biology is how these gradients regulate the differentiation and cellular location of the cells within the cryp. Identifying the morphogenetic factor concentration regulating the microenvironment is of utmost importance in combatting CRC. Because Wnt-signaling is hypothesized to maintain stem cells as well as cancer cells, the ability to positivity or negatively modulate the Wnt-pathway may be of therapeutic relevance. Nonetheless, lack of appropriate in vitro intestinal models systems has limited the ability to test this hypothesis. To fully understand how tissues form and function, assays need to address how cells behave as a part of whole organ systems, within dynamic, heterogeneous microenvironments. Advances in culture techniques now enable long-term ex vivo expansion of organoids derived from colonic crypts, termed colonoids, which possess stem cells and all appropriate differentiated lineages. Despite the potential of these culture systems, the differentiated cell types exist randomly distributed within the colonoids, likely due to the absence of protein gradients present in vivo. Standard tissue culture dishes, which have been the gold-standard for culture of intestinal crypts, are incompatible with gradient generation. While microfluidic devices have been described for a number of assays on gut physiology, there have been no efforts aimed at recapitulating the biochemical signaling within the intestine, which biologists argue is the key orchestrator of the intestine's remarkable regenerative potential. This microdevice proposed in this research will be an innovative approach to assess the impact of biological gradients on colonic stem cell behavior. This microengineered technology will be developed to introduce tightly controlled gradients of relevant morphogenetic factors to primary colonic cells to elucidate contributions of individual factors on colonic stem cell expansion. This tool will also act as an enabling technology to introduce Wnt-3a gradients to crypt microenvironment obtained from CRC murine model. Fluorescent measurements will be utilized as functional biological readouts to understand how microenvironmental cues affect normal and Wnt-driven CRC epithelium differently.
This work will design, develop, validate and utilize a microengineered device to assess the impact of linear factor gradients on the maintenance of the intestinal stem cell niche. The novel device will be used to elucidate threshold factor concentrations for stem-cell maintenance and will explore how a specific signaling pathway is implicated differently in healthy and disease state epithelium.