SNX3 recruits to phagosomes and negatively regulates phagocytosis in dendritic cells

Phagocytes such as dendritic cells (DC) and macrophages employ phagocytosis to take up pathogenic bacteria into phagosomes, digest the bacteria and present the bacteria‐derived peptide antigens to the adaptive immunity. Hence, efficient antigen presentation depends greatly on a well‐regulated phagocytosis process. Lipids, particularly phosphoinositides, are critical components of the phagosomes. Phosphatidylinositol‐3,4,5‐triphosphate [PI(3,4,5)P₃] is formed at the phagocytic cup, and as the phagosome seals off from the plasma membrane, rapid disappearance of PI(3,4,5)P₃ is accompanied by high levels of phosphatidylinositol‐3‐phosphate (PI3P) formation. The sorting nexin (SNX) family consists of a diverse group of Phox‐homology (PX) domain‐containing cytoplasmic and membrane‐associated proteins that are potential effectors of phosphoinositides. We hypothesized that SNX3, a small sorting nexin that contains a single PI3P lipid‐binding PX domain as its only protein domain, localizes to phagosomes and regulates phagocytosis in DC. Our results show that SNX3 recruits to nascent phagosomes and silencing of SNX3 enhances phagocytic uptake of bacteria by DC. Furthermore, SNX3 competes with PI3P lipid‐binding protein, early endosome antigen‐1 (EEA1) recruiting to membranes. Our results indicate that SNX3 negatively regulates phagocytosis in DC possibly by modulating recruitment of essential PI3P lipid‐binding proteins of the phagocytic pathways, such as EEA1, to phagosomal membranes.     

The development of silk fibroin scaffolds using an indirect rapid prototyping approach: Morphological analysis and cell growth monitoring by spectral-domain optical coherence tomography

To date, naturally derived biomaterials are rarely used in advanced tissue engineering (TE) methods despite their superior biocompatibility. This is because these native materials, which consist mainly of proteins and polysaccharides, do not possess the ability to withstand harsh processing conditions. Unlike synthetic polymers, natural materials degrade and decompose rapidly in the presence of chemical solvents and high temperature, respectively. Thus, the fabrication of tissue scaffolds using natural biomaterials is often carried out using conventional techniques, where the efficiency in mass transport of nutrients and removal of waste products within the construct is compromised. The present study identified silk fibroin (SF) protein as a suitable material for the application of rapid prototyping (RP) or additive manufacturing (AM) technology. Using the indirect RP method, via the use of a mould, SF tissue scaffolds with both macro- and micro-morphological features can be produced and qualitatively examined by spectral-domain optical coherence tomography (SD-OCT). The advanced imaging technique showed the ability to differentiate the cells and SF material by producing high contrasting images, therefore suggesting the method as a feasible alternative to the histological analysis of cell growth within tissue scaffolds.     

A comparison of the clinical, demographic and psychiatric profiles among patients with erosive and non-erosive reflux disease in a multi-ethnic Asian country

AIM: To examine the clinical spectrum of gastroesophageal reflux disease (GERD) and compare erosive (ERD) with non-erosive (NERD) in terms of clinical, demographic and psychiatric profiles. METHODS: Patients with reflux symptoms were enrolled and stratified to NERD and ERD after endoscopy (LA classification). Patients with ERD presenting with dyspepsia were included. Patients on proton pump inhibitors (PPI) or H2 receptor antagonists before endoscopy were excluded. Demographic data, Helicobacter pylori(H pylori) status and presence of minor psychiatric morbidity (based on General Health Questionnaire-28) were analyzed. RESULTS: Among 690 patients screened, 533 were eligible for analysis (male to female ratio: 3:2; Chinese: 75.4%; Malay: 9.8%; Indian: 14.8%). Clinical spectrum of GERD: N: 40.5%; A: 46%; B: 9.2%; C: 2.1%; D: 0.6%; Barrett's esophagus: 1.7%. Compared to patients with NERD, patients with ERD were significantly older (45 vs 39.4 years), more likely to be male (64.4% vs 53.7%), tended to smoke (19.6% vs 9.7%), less likely to have minor psychiatric morbidity (26.4 vs 46.7%) and were more likely to respond to PPI (79.7 vs 66.8%). There was also a trend towards a higher BMI (24.5 vs 23.5). Race, alcohol consumption and H pylori status were not significant. On multivariate analysis, age and presence of minor psychiatric morbidity remained with significant differences. CONCLUSION: The majority of patients who have typical symptoms of GERD have NERD or mild erosive reflux disease. Compared to patients with erosive reflux disease, patients with NERD were younger and had a higher prevalence of minor psychiatric morbidity.     

Involvement of guanine nucleotide binding proteins in neutrophil activation and priming by GM-CSF

Pre-incubation of human neutrophils with pertussis toxin significantly inhibited the neutrophil-directed biologic actions of granulocyte- macrophage colony-stimulating factor (GM-CSF) in three separate assays: the induction of c-fos mRNA, the enhancement of both platelet- activating factor-induced mobilization of intracellular calcium, and stimulation of leukotriene synthesis by the calcium ionophore A23187. Cholera toxin did not have an effect on the latter two assays. Pre- treatment of human neutrophils with pertussis toxin did not affect the binding of GM-CSF to its surface receptor. These results provide the first evidence that a pertussis toxin substrate plays an important mediatory role in the mechanism of action of GM-CSF.