Absence of Receptor Guanylyl Cyclase C Enhances Ileal Damage and Reduces Cytokine and Antimicrobial Peptide Production during Oral Salmonella enterica Serovar Typhimurium Infection.

Nontyphoidal Salmonella disease contributes toward significant morbidity and mortality across the world. Host factors, including gamma interferon, tumor necrosis factor alpha, and gut microbiota, significantly influence the outcome of Salmonella pathogenesis. However, the entire repertoire of host protective mechanisms contributing to Salmonella pathogenicity is not completely appreciated. Here, we investigated the roles of receptor guanylyl cyclase C (GC-C), which is predominantly expressed in the intestine and regulates intestinal cell proliferation and fluid-ion homeostasis. Mice deficient in GC-C (Gucy2c-/-) displayed accelerated mortality compared with that for wild-type mice following infection via the oral route, even though both groups possessed comparable systemic Salmonella infection burdens. Survival following intraperitoneal infection remained similar in both groups, indicating that GC-C offered protection via a gut-mediated response. The serum cortisol level was higher in Gucy2c-/- mice than wild-type (Gucy2c+/+) mice, and an increase in infection-induced thymic atrophy with a loss of immature CD4+ CD8+ double-positive thymocytes was observed. Accelerated and enhanced damage in the ileum, including submucosal edema, epithelial cell damage, focal tufting, and distortion of the villus architecture, was seen in Gucy2c-/- mice concomitantly with a larger number of ileal tissue-associated bacteria. Transcription of key mediators of Salmonella-induced inflammation (interleukin-22/Reg3ß) was altered in Gucy2c-/- mice in comparison to that in Gucy2c+/+ mice. A reduction in fecal lactobacilli, which are protective against Salmonella infection, was observed in Gucy2c-/- mice. Gucy2c-/- mice cohoused with wild-type mice continued to show reduced amounts of lactobacilli and increased susceptibility to infection. Our study, therefore, suggests that the receptor GC-C confers a survival advantage during gut-mediated Salmonella enterica serovar Typhimurium pathogenesis, presumably by regulating Salmonella effector mechanisms and maintaining a beneficial microbiome.

How safe are magnetic nanomotors: From cells to animals.

Helical magnetic nanomotors can be actuated using an external magnetic field and have potential applications in drug delivery, colloidal manipulation, and bio-microrheology. Recently, they have been maneuvered in biological environments such as vitreous humour, dentinal tubules, peritoneal fluid, stromal matrix, and blood, which are promising developments for clinical applications. However, their biocompatibility and biodistribution are vital parameters that must be assessed before further use. An extensive quantitative evaluation has been performed for these parameters for the first time through in vitro and in vivo experiments. Investigations of cell death, proliferation, and DNA damage ascertain that the motors are non-toxic. Also, an unbiased transcriptomic analysis affirms that the motors are not genotoxic till 20 motors/ cell. Toxicity studies in mice reveal that the motors show no signs of toxicity up to a dose of 55 mg/ kg body weight. Further, the biodistribution studies show that they remain in the blood circulation after injection and at later stages possibly adhere to the walls of the blood vessel because of adsorption. However, perfusion with physiological saline decreases this adsorption/adhesion. Overall, we demonstrate the biocompatibility of nanomotors in live cellular and organismal systems, and a systemic biodistribution analysis reveals organ-specific retention of motors.

Gut-associated cGMP mediates colitis and dysbiosis in a mouse model of an activating mutation in GUCY2C.

Activating mutations in receptor guanylyl cyclase C (GC-C), the target of gastrointestinal peptide hormones guanylin and uroguanylin, and bacterial heat-stable enterotoxins cause early-onset diarrhea and chronic inflammatory bowel disease (IBD). GC-C regulates ion and fluid secretion in the gut via cGMP production and activation of cGMP-dependent protein kinase II. We characterize a novel mouse model harboring an activating mutation in Gucy2c equivalent to that seen in an affected Norwegian family. Mutant mice demonstrated elevated intestinal cGMP levels and enhanced fecal water and sodium content. Basal and linaclotide-mediated small intestinal transit was higher in mutant mice, and they were more susceptible to DSS-induced colitis. Fecal microbiome and gene expression analyses of colonic tissue revealed dysbiosis, up-regulation of IFN-stimulated genes, and misregulation of genes associated with human IBD and animal models of colitis. This novel mouse model thus provides molecular insights into the multiple roles of intestinal epithelial cell cGMP, which culminate in dysbiosis and the induction of inflammation in the gut.