Project Summary ADAM17 loss of function (LOF) is the cause of a pediatric enteropathy termed Neonatal Inflammatory Skin and Bowel Disease 1 (NISBD1), which is associated with intestinal inflammation and diarrhea. While little is known about NISBD1, two patient biopsies revealed abnormal intestinal crypt/villus morphology. The crypt/villus structure is the fundamental repeating intestinal unit lined by an epithelium that contains crypt restricted intestinal stem cells (ISCs). ISCs give rise to differentiated cells and are integral to maintaining epithelial function. ISCs are supported by specialized epithelial cells and underlying mesenchymal cells that provide ISC niche signals, including EGF-like ligands. ADAM17 is a ubiquitously expressed protease that cleaves and sheds proteins from the cell membrane. Its substrates include EGF-like ligands, suggesting a role for ADAM17 in the ISC niche. Recent work has revealed that ErbB3 ligand neuregulin 1 (NRG1) promotes human ISC maturation and differentiation. Human fetal intestinal tissue sections reveal mesenchyme restricted expression of NRG1 and epithelium restricted expression of its receptor ErbB3. This suggests a pattern of ADAM17 mediated mesenchyme to epithelium signaling crosstalk. I will test the hypothesis that ADAM17 mediates cellular crosstalk, regulating human intestinal epithelial development. First, I am establishing a matched isogenic set of NISBD1 patient iPSC lines with one CRISPR corrected to be ADAM17 proficient. I will differentiate both lines into human intestinal organoids containing organized epithelium and mesenchyme. Then, I will interrogate the ADAM17 LOF phenotype using cellular, transcriptomic, and functional analyses. Next, I will investigate ADAM17 mediated cellular crosstalk in a targeted approach by studying NRG1-ErbB3 signaling. To identify additional candidate ADAM17 substrates, I will take an unbiased mass spectrometry and proteomics approach to determine all human intestinal ADAM17 substrates, i.e. the sheddome. This analysis will establish datasets for future targeted investigation of ADAM17 substrates in the human ISC niche. In summary, I will perform an innovative patient specific disease modeling study using iPSC-derived organoids to characterize NISBD1 and study the role of ADAM17 in the developing human intestine.