Smad7 interrupts TGF-β signaling in intestinal macrophages and promotes inflammatory activation of these cells during necrotizing enterocolitis

Functional macrophages and gastrointestinal disorders

Macrophages (MΦ) differentiate from blood monocytes and participate in innate and adaptive immunity. Because of their abilities to recognize pathogens and activate bactericidal activities, MΦ are always discovered at the site of immune defense. MΦ in the intestine are unique, such that in the healthy intestine, they possess complex mechanisms to protect the gut from inflammation. In these complex mechanisms, they produce anti-inflammatory cytokines, such as interleukin-10 and transforming growth factor-β, and inhibit the inflammatory pathways mediated by Toll-like receptors. It has been demonstrated that resident MΦ play a crucial role in maintaining intestinal homeostasis, and they can be recognized by their unique markers. Nonetheless, in the inflamed intestine, the function of MΦ will change because of environmental variation, which may be one of the mechanisms of inflammatory bowel disease (IBD). We provide further explanation about these mechanisms in our review. In addition, we review recent discoveries that MΦ may be involved in the development of gastrointestinal tumors. We will highlight the possible therapeutic targets for the management of IBD and gastrointestinal tumors, and we also discuss why more details are needed to fully understand all other effects of intestinal MΦ.

Neonatal intestinal dysbiosis in necrotizing enterocolitis

Necrotizing Enterocolitis (NEC) is one of the most devastating gastrointestinal diseases in neonates, particularly among preterm infants in whom surgical NEC is the leading cause of morbidity. NEC pathophysiology occurs in the hyper-reactive milieu of the premature gut after bacterial colonization. The resultant activation of the TLR4 pathway appears to be a strongly contributing factor. Advancements in metagenomics may yield new clarity to the relationship between the neonatal intestinal microbiome and the development of NEC. After a century without effective directed treatments, microbiome manipulation offers a promising therapeutic target for the prevention and treatment of this devastating disease.

Selenium and Selenoproteins in Gut Inflammation-A Review

Inflammatory bowel disease (IBD), characterized by severe flares and remissions, is a debilitating condition. While the etiology is unknown, many immune cells, such as macrophages, T cells and innate lymphoid cells, are implicated in the pathogenesis of the disease. Previous studies have shown the ability of micronutrient selenium (Se) and selenoproteins to impact inflammatory signaling pathways implicated in the pathogenesis of the disease. In particular, two transcription factors, nuclear factor-κB (NF-κB), and peroxisome proliferator activated receptor (PPAR)γ, which are involved in the activation of immune cells, and are also implicated in various stages of inflammation and resolution, respectively, are impacted by Se status. Available therapies for IBD produce detrimental side effects, resulting in the need for alternative therapies. Here, we review the current understanding of the role of NF-κB and PPARγ in the activation of immune cells during IBD, and how Se and selenoproteins modulate effective resolution of inflammation to be considered as a promising alternative to treat IBD.

Neonatal mice with necrotizing enterocolitis-like injury develop thrombocytopenia despite increased megakaryopoiesis

BACKGROUND

Thrombocytopenia is frequently encountered in infants with necrotizing enterocolitis (NEC). To develop a preclinical model of NEC-related thrombocytopenia, we measured serial platelet counts in 10-d-old (P10) mouse pups with trinitrobenzene sulfonic acid (TNBS)-induced NEC-like injury. We also measured platelet volume indices, immature platelet fraction (IPF), and megakaryocyte number/ploidy in these animals.

METHODS

Platelet counts, platelet volume indices, and IPF were measured in control (N = 65) and TNBS-treated pups (N = 104) using an automated hematology analyzer. Bone marrow megakaryocyte number, ploidy and CD41 expression were measured by flow cytometry. These findings were confirmed in a small cohort of P3 mice with NEC-like injury.

RESULTS

Murine pups with TNBS-mediated NEC-like injury developed thrombocytopenia at 15-24 h after exposure to TNBS. Intestinal injury was associated with increased platelet volume indices (mean platelet volume, platelet-to-large cell ratio, and platelet distribution width), and IPF, indicating increased thrombopoiesis. These mice also showed increased megakaryocyte number, ploidy, and CD41 expression, indicating increased megakaryocyte differentiation.

CONCLUSION

Similar to human NEC, murine NEC-like injury was also associated with decreased platelet counts. There was evidence of increased megakaryocyte differentiation and thrombopoiesis, which favors peripheral consumption of platelets as the likely mechanism of thrombocytopenia in these animals, over decreased platelet production.

Pathogenesis of NEC: Role of the innate and adaptive immune response

Necrotizing enterocolitis (NEC) is a devastating disease in premature infants with high case fatality and significant morbidity among survivors. Immaturity of intestinal host defenses predisposes the premature infant gut to injury. An abnormal bacterial colonization pattern with a deficiency of commensal bacteria may lead to a further breakdown of these host defense mechanisms, predisposing the infant to NEC. Here, we review the role of the innate and adaptive immune system in the pathophysiology of NEC.

The Role of Mucosal Immunity in the Pathogenesis of Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is the most devastating gastrointestinal disease of prematurity. Although the precise cause is not well understood, the main risk factors thought to contribute to NEC include prematurity, formula feeding, and bacterial colonization. Recent evidence suggests that NEC develops as a consequence of intestinal hyper-responsiveness to microbial ligands upon bacterial colonization in the preterm infant, initiating a cascade of aberrant signaling events, and a robust pro-inflammatory mucosal immune response. We now have a greater understanding of important mechanisms of disease pathogenesis, such as the role of cytokines, immunoglobulins, and immune cells in NEC. In this review, we will provide an overview of the mucosal immunity of the intestine and the relationship between components of the mucosal immune system involved in the pathogenesis of NEC, while highlighting recent advances in the field that have promise as potential therapeutic targets. First, we will describe the cellular components of the intestinal epithelium and mucosal immune system and their relationship to NEC. We will then discuss the relationship between the gut microbiota and cell signaling that underpins disease pathogenesis. We will conclude our discussion by highlighting notable therapeutic advancements in NEC that target the intestinal mucosal immunity.

Trinitrobenzene sulfonic acid-induced intestinal injury in neonatal mice activates transcriptional networks similar to those seen in human necrotizing enterocolitis

BACKGROUND

We have shown previously that enteral administration of 2, 4, 6-trinitrobenzene sulfonic acid in 10-d-old C57BL/6 pups produces an acute necrotizing enterocolitis with histopathological and inflammatory changes similar to human necrotizing enterocolitis (NEC). To determine whether murine neonatal 2, 4, 6-trinitrobenzene sulfonic acid (TNBS)-mediated intestinal injury could be used as a NEC model, we compared gene expression profiles of TNBS-mediated intestinal injury and NEC.

METHODS

Whole-genome microarray analysis was performed on proximal colon from control and TNBS-treated pups (n = 8/group). For comparison, we downloaded human microarray data of NEC (n = 5) and surgical control (n = 4) from a public database. Data were analyzed using the software programs Partek Genomics Suite and Ingenuity Pathway Analysis.

RESULTS

We detected extensive changes in gene expression in murine TNBS-mediated intestinal injury and human NEC. Using fold-change cut-offs of ±1.5, we identified 4,440 differentially-expressed genes (DEGs) in murine TNBS-mediated injury and 1,377 in NEC. Murine TNBS-mediated injury and NEC produced similar changes in expression of orthologous genes (r = 0.611, P < 0.001), and also activated nearly-identical biological processes and pathways. Lipopolysaccharide was top predicted upstream regulator in both the murine and human datasets.

CONCLUSION

Murine neonatal TNBS-mediated enterocolitis and human NEC activate nearly-identical biological processes, signaling pathways, and transcriptional networks.

Necrotizing enterocolitis: new insights into pathogenesis and mechanisms

Necrotizing enterocolitis (NEC) is the most frequent and lethal disease of the gastrointestinal tract of preterm infants. At present, NEC is thought to develop in the premature host in the setting of bacterial colonization, often after administration of non-breast milk feeds, and disease onset is thought to be due in part to a baseline increased reactivity of the premature intestinal mucosa to microbial ligands as compared with the full-term intestinal mucosa. The increased reactivity leads to mucosal destruction and impaired mesenteric perfusion and partly reflects an increased expression of the bacterial receptor Toll-like receptor 4 (TLR4) in the premature gut, as well as other factors that predispose the intestine to a hyper-reactive state in response to colonizing microorganisms. The increased expression of TLR4 in the premature gut reflects a surprising role for this molecule in the regulation of normal intestinal development through its effects on the Notch signalling pathway. This Review will examine the current approach to the diagnosis and treatment of NEC, provide an overview of our current knowledge regarding its molecular underpinnings and highlight advances made within the past decade towards the development of specific preventive and treatment strategies for this devastating disease.