Post-weaning gut microbiota colonization in germ-free mice results in crinophagy-like granule abnormalities and apoptosis in Paneth cells.

The gut microbiota plays a critical role in maintaining host homeostasis by supporting intestinal epithelial cell function. Paneth cells, located at the base of small intestinal crypts, regulate the gut microbiota through secretion of granules containing antimicrobial substances. Previous studies have reported quantitative and functional impairments of Paneth cells in germ-free (GF) mice lacking the gut microbiota. However, it remains unclear whether the acquired gut microbiota colonization following microbiota deficiency can restore these impairments. In this study, we investigated the effects of post-weaning gut microbiota colonization on the cellular properties of Paneth cells in GF mice. Three-week-old GF mice were co-housed with conventional (CV) mice for 12 weeks to establish an ex-germ-free (ExGF) model in which a microbiota was colonized in adulthood. Although ExGF mice restored the gut microbiota diversity to levels comparable to that of CV mice, the reduction in Paneth cell numbers observed in GF mice was not fully restored. Furthermore, Paneth cells in ExGF mice exhibited increased numbers of abnormal crinophagy-like secretory granules and elevated apoptosis. These findings indicate that gut microbiota colonization following microbiota deficiency does not fully restore Paneth cell properties and is associated with abnormal morphological changes and apoptosis. These results suggest that Paneth cells that develop in the absence of early-life microbial stimulation may respond differently to subsequent microbial colonization, providing novel insight into host-microbiota interactions during intestinal colonization.