Natural compound methyl protodioscin protects against intestinal inflammation through modulation of intestinal immune responses.

Dioscoreaceae, a kind of yam plant, has been recommended for treatment of chronic inflammatory conditions. However, the mechanisms are poorly defined. Methyl protodioscin (MPD) is one of the main bioactive components in Dioscoreaceae. Here, we aim to determine the mechanisms by which MPD ameliorates intestinal inflammation. Surgical intestinal specimens were collected from inflammatory bowel diseases (IBD) patients to perform organ culture. Experimental colitis was induced in mice by dextran sulfate sodium (DSS) or Citrobacter rodentium, and was then treated with MPD. NF-κB activation, expression of mucosal pro-inflammatory cytokines, disease severity, and epithelial proliferation/apoptosis were determined. Mouse crypts and Caco-2 monolayers were cultured to observe the effect of MPD upon intestinal epithelial differentiation and barrier function. We found that MPD increased the percentage of survival from high-dose DSS-(4%) treated mice, and accelerated mucosal healing and epithelial proliferation in low-dose DSS-(2.5%) treated mice characterized by marked reduction in NF-κB activation, pro-inflammatory cytokines expression and bacterial translocation. Consistently, MPD protected colonic mucosa from C. rodentium-induced colonic inflammation and bacterial colonization. In vitro studies showed that MPD significantly increased crypt formation and restored intestinal barrier dysfunction induced by pro-inflammatory cytokines. In conclusion, MPD ameliorates the intestinal mucosal inflammation by modulating the intestinal immunity to enhance intestinal barrier differentiation. MPD could be an alternative for treating chronic intestinal inflammatory diseases.

Immunosuppressive CD71+ erythroid cells compromise neonatal host defence against infection.

Newborn infants are highly susceptible to infection. This defect in host defence has generally been ascribed to the immaturity of neonatal immune cells; however, the degree of hyporesponsiveness is highly variable and depends on the stimulation conditions. These discordant responses illustrate the need for a more unified explanation for why immunity is compromised in neonates. Here we show that physiologically enriched CD71(+) erythroid cells in neonatal mice and human cord blood have distinctive immunosuppressive properties. The production of innate immune protective cytokines by adult cells is diminished after transfer to neonatal mice or after co-culture with neonatal splenocytes. Neonatal CD71(+) cells express the enzyme arginase-2, and arginase activity is essential for the immunosuppressive properties of these cells because molecular inhibition of this enzyme or supplementation with L-arginine overrides immunosuppression. In addition, the ablation of CD71(+) cells in neonatal mice, or the decline in number of these cells as postnatal development progresses parallels the loss of suppression, and restored resistance to the perinatal pathogens Listeria monocytogenes and Escherichia coli. However, CD71(+) cell-mediated susceptibility to infection is counterbalanced by CD71(+) cell-mediated protection against aberrant immune cell activation in the intestine, where colonization with commensal microorganisms occurs swiftly after parturition. Conversely, circumventing such colonization by using antimicrobials or gnotobiotic germ-free mice overrides these protective benefits. Thus, CD71(+) cells quench the excessive inflammation induced by abrupt colonization with commensal microorganisms after parturition. This finding challenges the idea that the susceptibility of neonates to infection reflects immune-cell-intrinsic defects and instead highlights processes that are developmentally more essential and inadvertently mitigate innate immune protection. We anticipate that these results will spark renewed investigation into the need for immunosuppression in neonates, as well as improved strategies for augmenting host defence in this vulnerable population.

Murine guanylate cyclase C regulates colonic injury and inflammation.

Guanylate cyclase C (GUCY2C or GC-C) and its ligands, guanylin (GUCA2A or Gn) and uroguanylin (GUCA2B or Ugn), are expressed in intestinal epithelial cells and regulate ion secretion, intestinal barrier function, and epithelial monolayer homeostasis via cGMP-dependent signaling pathways. The aim of this study was to determine whether GC-C and its ligands direct the course of intestinal inflammation. In this article, we show that dextran sodium sulfate (DSS)-induced clinical disease and histological damage to the colonic mucosa were significantly less severe in GC-C(-/-) mice and moderately reduced in Gn(-/-) animals. Relative to wild-type controls, GC-C(-/-) and Gn(-/-) mice had reduced apoptosis and increased proliferation of intestinal epithelial cells during DSS colitis. Basal and DSS-induced production of resistin-like molecule ß (RELMß) was substantially diminished in GC-C(-/-) mice. RELMß is thought to stimulate cytokine production in macrophages in this disease model and, consistent with this, TNF-α and IFN-γ production was minimal in GC-C(-/-) animals. RELMß and cytokine levels were similar to wild-type in Gn(-/-) mice, however. Colonic instillation of recombinant RELMß by enema into GC-C(-/-) mice restores sensitivity to DSS-mediated mucosal injury. These findings demonstrate a novel role for GC-C signaling in facilitating mucosal wounding and inflammation, and further suggest that this may be mediated, in part, through control of RELMß production.

Molecular cloning and promoter analysis of downregulated in adenoma (DRA).

Downregulated in adenoma (DRA), also referred to as SLC26A3, is an intestinal anion transporter essential for intestinal chloride absorption. Mutations in DRA result in congenital chloride diarrhea. DRA expression has been shown to be induced by differentiation and to be modulated by cytokines. However, mechanisms of DRA gene transcription and its tissue-specific targeting have not yet been investigated. In this study, we cloned a 3,765-bp promoter fragment of human DRA gene and characterized its activity in human colonic LS174T and Caco-2 human colon cell lines. Primer extension identified a single transcriptional initiation site that was identical in both colon cancer cell lines and normal colon. Although hepatic nuclear factor HNF-4 is involved in the basal activity of DRA promoter, sodium butyrate induces its activity in LS174T cells via the binding of Yin Yang 1 (YY1) and GATA transcription factors to their respective cis-elements in promoter region. We also demonstrated a reduction in DRA promoter activity in Caco-2 cells by IFN-gamma, suggesting that regulation of DRA promoter by IFN-gamma may contribute to the pathophysiology of intestinal inflammation. Furthermore, we showed that the DRA promoter fragment is sufficient to drive human growth hormone transgene expression specifically in villus epithelial cells of the small intestine and in differentiated upper crypt and surface epithelial cells of the colon. Our studies provide evidence for the involvement of HNF-4, YY1, and GATA transcription factors in DRA expression in intestinal differentiated epithelial cells.