No abstract

The vasculature in the spleen and peripheral lymph nodes (pLNs) is considerably different, which affects both homing of lymphocytes and antigenic access to these peripheral lymphoid organs. In this paper, we demonstrate that in mice lacking the homeodomain transcription factor Nkx2-3, the spleen develops a pLN-like mRNA expression signature, coupled with the appearance of high endothelial venules (HEVs) that mediate L-selectin–dependent homing of lymphocytes into the mutant spleen. These ectopic HEV-like vessels undergo postnatal maturation and progressively replace MAdCAM-1 by pLN addressin together with the display of CCL21 arrest chemokine in a process that is reminiscent of HEV formation in pLNs. Similarly to pLNs, development of HEV-like vessels in the Nkx2-3–deficient spleen depends on lymphotoxin-β receptor-mediated signaling. The replacement of splenic vessels with a pLN-patterned vasculature impairs the recirculation of adoptively transferred lymphocytes and reduces the uptake of blood-borne pathogens. The Nkx2-3 mutation in BALB/c background causes a particularly disturbed splenic architecture, characterized by the near complete lack of the red pulp, without affecting lymph nodes. Thus, our observations reveal that the organ-specific patterning of splenic vasculature is critically regulated by Nkx2-3, thereby profoundly affecting the lymphocyte homing mechanism and blood filtering capacity of the spleen in a tissue-specific manner.

Reactive oxygen species (ROS) and nitrogen species have an indispensable role in regulating cell signalling pathways, including transcriptional control via hypoxia inducible factor-1α (HIF-1α). Hyperbaric oxygenation treatment (HBO2) increases tissue oxygen content and leads to enhanced ROS production. In the present study DSS-induced colitis has been employed in BALB/c mice as an experimental model of gut mucosa inflammation to investigate the effects of HBO2 on HIF-1α, antioxidative enzyme, and proinflammatory cytokine genes during the colonic inflammation. Here we report that HBO2 significantly reduces severity of DSS-induced colitis, as evidenced by the clinical features, histological assessment, impaired immune cell expansion and mobilization, and reversal of IL-1β, IL-2, and IL-6 gene expression. Gene expression and antioxidative enzyme activity were changed by the HBO2 and the inflammatory microenvironment in the gut mucosa. Strong correlation of HIF-1α mRNA level to GPx1, SOD1, and IL-6 mRNA expression suggests involvement of HIF-1α in transcriptional regulation of these genes during colonic inflammation and HBO2. This is further confirmed by a strong correlation of HIF-1α with known target genes VEGF and PGK1. Results demonstrate that HBO2 has an anti-inflammatory effect in DSS-induced colitis in mice, and this effect is at least partly dependent on expression of HIF-1α and antioxidative genes.

Understanding the molecular mechanisms inducing and regulating epithelial-to-mesenchymal transition (EMT) upon chronic intestinal inflammation is critical for understanding the exact pathomechanism of inflammatory bowel disease (IBD). The aim of this study was to determine the expression profile of TAM family receptors in an inflamed colon. For this, we used a rat model of experimental colitis and also collected samples from colons of IBD patients. Samples were taken from both inflamed and uninflamed regions of the same colon; the total RNA was isolated, and the mRNA and microRNA expressions were monitored. We have determined that AXL is highly induced in active-inflamed colon, which is accompanied with reduced expression of AXL-regulating microRNAs. In addition, the expression of genes responsible for inducing or maintaining mesenchymal phenotype, such as SNAI1, ZEB2, VIM, MMP9, and HIF1α, were all significantly induced in the active-inflamed colon of IBD patients while the epithelial marker E-cadherin (CDH1) was downregulated. We also show that, in vitro, monocytic and colonic epithelial cells increase the expression of AXL in response to LPS or TNFα stimuli, respectively. In summary, we identified several interacting genes and microRNAs with mutually exclusive expression pattern in active-inflamed colon of IBD patients. Our results shed light onto a possible AXL- and microRNA-mediated regulation influencing epithelial-to-mesenchymal transition in IBD.

Although the homing of lymphocytes to GALT has been extensively studied, little is known about how high endothelial venules (HEVs) within Peyer’s patches (PPs) are patterned to display dominantly mucosal addressin cell adhesion molecule 1 (MAdCAM-1). In this study, we report that Nkx2-3–deficient mice show gradual loss of MAdCAM-1 in PPs postnatally and increased levels of mRNA for peripheral lymph node addressin (PNAd) backbone proteins as well as enhanced expression of MECA79 sulfated glycoepitope at the luminal aspect of HEVs, thus replacing MAdCAM-1 with PNAd. Induction of PNAd in mutant PPs requires lymphotoxin β receptor activity, and its upregulation needs the presence of mature T and B cells. Furthermore, treatment with MECA-79 anti-PNAd mAb in vivo effectively blocks lymphocyte homing to mutant PPs. Despite the replacement of MAdCAM-1 by PNAd in HEV endothelia, lymphocytes could efficiently home to PPs in mutant mice. We conclude that although Nkx2-3 activity controls the addressin balance of HEVs in GALT, the general HEV functionality is preserved independently from Nkx2-3, indicating a substantial plasticity in the specification of GALT HEV endothelium.