The intestine not only plays a role in fundamental processes in digestion and nutrient absorption, but it also has a role in eliminating ingested pathogenic bacteria and viruses. Paneth cells, which reside at the base of small intestinal crypts, secrete α-defensins and contribute to enteric innate immunity through potent microbicidal activities. However, the relationship between food factors and the innate immune functions of Paneth cells remains unknown. Here, we examined whether short-chain fatty acids and amino acids induce α-defensin secretion from Paneth cells in the isolated crypts of small intestine. Butyric acid and leucine elicit α-defensin secretion by Paneth cells, which kills Salmonella typhimurium. We further measured Paneth cell secretion in response to butyric acid and leucine using enteroids, a three-dimensional ex vivo culture system of small intestinal epithelial cells. Paneth cells expressed short-chain fatty acid receptors, Gpr41, Gpr43, and Gpr109a mRNAs for butyric acid, and amino acid transporter Slc7a8 mRNA for leucine. Antagonists of Gpr41 and Slc7a8 inhibited granule secretion by Paneth cells, indicating that these receptor and transporter on Paneth cells induce granule secretion. Our findings suggest that Paneth cells may contribute to intestinal homeostasis by secreting α-defensins in response to certain nutrients or metabolites.

Significance: Paneth cells produce granules containing antimicrobial peptides, such as α-defensin for host defense. Examination of the production and utilization of fucosyltransferase 2 (Fut2) by Paneth cells revealed two distinct subsets: Fut2⁺Paneth cells and Fut2⁻Paneth cells. Compared with Fut2⁻Paneth cells, Fut2⁺Paneth cells were enriched in granules containing antimicrobial peptides. IL-22 and IL-17a were found to be essential for commensal bacteria-dependent Fut2⁺Paneth cell development and function as part of gut defense.

Crohn’s disease (CD) is an intractable inflammatory bowel disease, and dysbiosis, disruption of the intestinal microbiota, is associated with CD pathophysiology. ER stress, disruption of ER homeostasis in Paneth cells of the small intestine, and α-defensin misfolding have been reported in CD patients. Because α-defensins regulate the composition of the intestinal microbiota, their misfolding may cause dysbiosis. However, whether ER stress, α-defensin misfolding, and dysbiosis contribute to the pathophysiology of CD remains unknown. Here, we show that abnormal Paneth cells with markers of ER stress appear in SAMP1/YitFc, a mouse model of CD, along with disease progression. Those mice secrete reduced-form α-defensins that lack disulfide bonds into the intestinal lumen, a condition not found in normal mice, and reduced-form α-defensins correlate with dysbiosis during disease progression. Moreover, administration of reduced-form α-defensins to wild-type mice induces the dysbiosis. These data provide novel insights into CD pathogenesis induced by dysbiosis resulting from Paneth cell α-defensin misfolding and they suggest further that Paneth cells may be potential therapeutic targets.

Live imaging visualizes the structure, dynamics, and function of cells and tissues to reveal the molecular mechanisms, and has contributed to the advancement of life science. In live imaging, it has been well known that there is a trade-off between higher-resolution analysis and cell damage caused by light illumination, i.e., phototoxicity. However, despite the risk of unknowingly distorting experimental results, phototoxicity is an unresolved issue in live imaging because overall consequences occurring inside cells due to phototoxicity remains unknown. Here, we determined the molecular process of phototoxicity-induced cell damage systematically under low- and high-dose light illumination conditions by analyzing differential gene expression using RNA-sequencing in a three-dimensional organoid of small intestinal epithelial cells, enteroid. The low-dose light illumination already induced various abnormalities in functional molecules involved in the response to reactive oxygen species generated by the excitation of fluorescent dyes, intracellular metabolism, mitosis, immune responses, etc., at mRNA expression level. Together with the behavior toward apoptosis caused by high-dose light illumination, the light dose-dependent progression of intracellular damage was revealed. About visible impairment of intestinal epithelial function, failures in both the structure-forming ability of enteroids and Paneth cell granule secretion were observed under high-dose light illumination, while the drug efflux was not disturbed despite abnormal drug efflux transporter mRNA expression. Based on the gene expression profiles, we comprehensively clarified phenomena in the cells at mRNA level that cannot be recognized both morphologically and functionally during live imaging, further providing a new insight into the risk of phototoxicity. This study warns from the aspect of mRNA expression that awareness of phototoxic artifacts is needed when analyzing cellular function and the mechanism in live imaging.

Background: Bifidobacterium colonization of the intestine is believed to have beneficial effects on our health from infancy throughout life. However, how particular members of the genus Bifidobacterium colonize the neonatal intestine and whether early-life bifidobacterial colonization affects establishment of Bifidobacterium-rich microbiota in later life remain unanswered. α-Defensin secreted from small intestinal Paneth cells elicits selective bactericidal activities that efficiently kill pathogens while hardly affecting commensals including Bifidobacterium in vitro, thus contributing to intestinal microbiota regulation. Methods: One hundred forty-eight fecal samples were serially obtained from 33 children from postnatal 3–5 days to 3 years old, conducting a longitudinal cohort study of mothers and children living in Iwamizawa city, Hokkaido, Japan (SMILE Iwamizawa study). Microbiota composition and secretory level of α-defensin, human defensin 5 (HD5), were assessed to investigate the relationship between HD5 and Bifidobacterium colonization. Results: We show that HD5 is associated with colonization of Bifidobacterium in early life from pre-weaning to weaning periods. Furthermore, high relative abundance of Bifidobacterium in the weaning period, which positively correlates with HD5 secretion, is associated with the establishment of Bifidobacterium-rich microbiota at 3 years old, when the intestinal microbiota matures. Conclusions: This study suggests the importance of the weaning period in establishing long-lasting homeostasis interwoven with the host innate immunity and Bifidobacterium in the intestinal microbiota.

Intestinal epithelial cells separate subepithelial tissues from luminal environment formed with food, incoming pathogens, and resident intestinal microbiota, etc., and elicit various intestinal function. Enteroid, a three-dimensional culture system of small intestinal epithelial cells, has been widely used for analyzing the intestinal function, further a transgenic enteroid was developed to investigate the molecular mechanisms. However, conventional transgenic enteroid production method, which transfer gene into single stem cells, has limitations including low efficiency and time-consuming. Here we show that by gene transfer into small intestinal isolated crypts maintaining stem cell niche, a transgenic enteroid was obtained quickly and efficiently. Isolated crypts were transfected by lentiviral vector without separating into single cells, and transgenic enteroid composed of all lineages of intestinal epithelial cells was generated at day 7 with yield of 56%, maintaining the intestinal function in drug transport and innate immunity. Our efficient and simple transgenic enteroid generation method enables high-throughput investigation of intestinal epithelial cells and contributes to understanding intestinal function.