SLC7A5 is critical for Paneth cell integrity and function

The intestine is the critical organ not only for processing and resorbing nutrients from ingested food but also for defending the organism from external stresses such as pathogens. These functions are mainly carried out by the epithelium which is constantly being self-renewed throughout adult life. Intestinal epithelial homeostasis is maintained through well-controlled cell proliferation of the stem cells and transient amplifying cells and the apoptotic degeneration of epithelial cells, mostly at or near the tip of the villi. Many genes and pathways have been found to influence intestinal epithelial cell proliferation. Among them is the mTORC1 signaling pathway, whose activation is known to increase cell proliferation. Here, we report the first intestinal epithelial specific knockout (IEC-KO) of an amino acid transporter capable of activating mTORC1. We show that the transporter, slc7a5, is highly expressed in the intestinal crypt and slc7a5 IEC-KO leads to expected reduction in mTORC1 signal in the crypt or even in intestinal organoids in vitro. Surprisingly, slc7a5 IEC-KO leads to increased proliferation of both transit amplifying cells and crypt base stem cells but a reduction in the secretory cells, particularly mature Paneth cells in the crypt base. Our scRNA-seq and electron microscopic analyses reveals that slc7a5 IEC-KO causes dedifferentiation of the Paneth cells, leading to drastically reduced secretory granules and lysozyme expression without affecting the overall Paneth cell number. We further show that slc7a5 IEC-KO mice are prone to induced colitis due to this loss of Paneth cell differentiation. We propose a model where slc7a5 regulates secretory cell differentiation to affect stem cell niche and/or inflammatory response to regulate cell proliferation in the crypts.