The Zinc Transporter ZnT2 is Necessary for Stabilization of Granule Contents in Intestinal Paneth Cell Granules

Abstract

Paneth cells (PC) are secretory cells in small intestinal crypts that play a critical role in self‐protection against luminal pathogens. Defects in PC function are associated with necrotizing enterocolitis and Crohn's disease. PCs release granules containing a host of antimicrobial peptides and a large amount of zinc (Zn). Zn prevents degradation of α ‐defensins and stabilizes lysozyme in its monomeric active conformation. How Zn accumulates in PC granules is not understood. We used wild‐type (WT) and ZnT2‐null (KO) mice to determine the role of ZnT2 in PC function. ZnT2 was expressed in crypts and localized to PC granules by immunofluorescence and sucrose gradient fractionation. Studies using the fluorescent Zn reporter ZP1 indicated that KO mice were unable to accumulate Zn into granules. While no morphologic abnormalities were observed in the intestines of KO mice, a significantly greater number of PCs were degranulated compared with PCs in WT mice (p<0.01), and PCs in KO mice had profound defects in sub‐cellular organization. In response to saline perfusion, ileal segments from KO mice retained less overall (p<0.01), and significantly more dimerized (less active) lysozyme (p<0.05), but released more lysozyme into the lumen (p<0.05). These data indicate that ZnT2 imports Zn into PC granules, and the inability to do so destabilizes granules and Zn‐requiring granule proteins and leads to defects in coordinated granule secretion, which may put an individual at risk for infection and inflammatory illness.