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A lacteal is a blunt‐ended, long, tube‐like lymphatic vessel located in the center of each intestinal villus that provides a unique route for drainage of absorbed lipids from the small intestine. However, key regulators for maintaining lacteal integrity are poorly understood. Here, we explore whether and how the gut microbiota regulates lacteal integrity. Germ depletion by antibiotic treatment triggers lacteal regression during adulthood and delays lacteal maturation during the postnatal period. In accordance with compromised lipid absorption, the button‐like junction between lymphatic endothelial cells, which is ultrastructurally open to permit free entry of dietary lipids into lacteals, is significantly reduced in lacteals of germ‐depleted mice. Lacteal defects are also found in germ‐free mice, but conventionalization of germ‐free mice leads to normalization of lacteals. Mechanistically, VEGF‐C secreted from villus macrophages upon MyD88‐dependent recognition of microbes and their products is a main factor in lacteal integrity. Collectively, we conclude that the gut microbiota is a crucial regulator for lacteal integrity by endowing its unique microenvironment and regulating villus macrophages in small intestine.

Genetic alterations that reduce the function of the immunoregulatory cytokine IL-10 contribute to colitis in mouse and man. Myeloid cells such as macrophages (MΦs) and dendritic cells (DCs) play an essential role in determining the relative abundance of IL-10 versus inflammatory cytokines in the gut. As such, using small molecules to boost IL-10 production by DCs-MΦs represents a promising approach to increase levels of this cytokine specifically in gut tissues. Toward this end, we screened a library of wellannotated kinase inhibitors for compounds that enhance production of IL-10 by murine bone-marrow-derived DCs stimulated with the yeast cell wall preparation zymosan. This approach identified a number of kinase inhibitors that robustly up-regulate IL-10 production including the Food and Drug Administration (FDA)-approved drugs dasatinib, bosutinib, and saracatinib that target ABL, SRC-family, and numerous other kinases. Correlating the kinase selectivity profiles of the active compounds with their effect on IL-10 production suggests that inhibition of salt-inducible kinases (SIKs) mediates the observed IL-10 increase. This was confirmed using the SIK-targeting inhibitor HG-9-91-01 and a series of structural analogs. The stimulatory effect of SIK inhibition on IL-10 is also associated with decreased production of the proinflammatory cytokines IL-1β, IL-6, IL-12, and TNF-α, and these coordinated effects are observed in human DCs-MΦs and anti-inflammatory CD11c + CX 3 CR1 hi cells isolated from murine gut tissue. Collectively, these studies demonstrate that SIK inhibition promotes an anti-inflammatory phenotype in activated myeloid cells marked by robust IL-10 production and establish these effects as a previously unidentified activity associated with several FDA-approved multikinase inhibitors.

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Fibroblastic reticular cells (FRCs) are immunologically specialized myofibroblasts of lymphoid organ, and FRC maturation is essential for structural and functional properties of lymph nodes (LNs). Here we show that YAP and TAZ (YAP/TAZ), the final effectors of Hippo signaling, regulate FRC commitment and maturation. Selective depletion of YAP/TAZ in FRCs impairs FRC growth and differentiation and compromises the structural organization of LNs, whereas hyperactivation of YAP/TAZ enhances myofibroblastic characteristics of FRCs and aggravates LN fibrosis. Mechanistically, the interaction between YAP/TAZ and p52 promotes chemokine expression that is required for commitment of FRC lineage prior to lymphotoxin-β receptor (LTβR) engagement, whereas LTβR activation suppresses YAP/TAZ activity for FRC maturation. Our findings thus present YAP/TAZ as critical regulators of commitment and maturation of FRCs, and hold promise for better understanding of FRC-mediated pathophysiologic processes.

Background and Aims Saccharomyces boulardii (Sb) can protect against intestinal injury and tumor formation, but how this probiotic yeast controls protective mucosal host responses is unclear. Angiogenesis is an integral process of inflammatory responses in inflammatory bowel diseases (IBD) and required for mucosal remodeling during restitution. The aim of this study was to determine whether Sb alters VEGFR (vascular endothelial growth factor receptor) signaling, a central regulator of angiogenesis.MethodsHUVEC were used to examine the effects of Sb on signaling and on capillary tube formation (using the ECMatrix™ system). The effects of Sb on VEGF-mediated angiogenesis were examined in vivo using an adenovirus expressing VEGF-A(164) in the ears of adult nude mice (NuNu). The effects of Sb on blood vessel volume branching and density in DSS-induced colitis was quantified using VESsel GENeration (VESGEN) software.Results1) Sb treatment attenuated weight-loss (p<0.01) and histological damage (p<0.01) in DSS colitis. VESGEN analysis of angiogenesis showed significantly increased blood vessel density and volume in DSS-treated mice compared to control. Sb treatment significantly reduced the neo-vascularization associated with acute DSS colitis and accelerated mucosal recovery restoration of the lamina propria capillary network to a normal morphology. 2) Sb inhibited VEGF-induced angiogenesis in vivo in the mouse ear model. 3) Sb also significantly inhibited angiogenesis in vitro in the capillary tube assay in a dose-dependent manner (p<0.01). 4) In HUVEC, Sb reduced basal VEGFR-2 phosphorylation, VEGFR-2 phosphorylation in response to VEGF as well as activation of the downstream kinases PLCγ and Erk1/2.ConclusionsOur findings indicate that the probiotic yeast S boulardii can modulate angiogenesis to limit intestinal inflammation and promote mucosal tissue repair by regulating VEGFR signaling.

The lymphatic vasculature has been regarded as a passive conduit for interstitial fluid and responsible for the absorption of macromolecules such as proteins or lipids and transport of nutrients from food. However, emerging data show that the lymphatic vasculature system plays an important role in immune modulation. One of its major roles is to coordinate antigen transport and immune-cell trafficking from peripheral tissues to secondary lymphoid organs, lymph nodes. This perspective was recently updated with the notion that the interaction between lymphatic endothelial cells and leukocytes controls the immune-cell migration and immune responses by regulating lymphatic flow and various secreted molecules such as chemokines and cytokines. In this review, we introduce the lymphatic vasculature networks and genetic transgenic models for research on the lymphatic vasculature system. Next, we discuss the contribution of lymphatic endothelial cells to the control of immune-cell trafficking and to maintenance of peripheral tolerance. Finally, the physiological roles and features of the lymphatic vasculature system are further discussed regarding inflammation-induced lymphangiogenesis in a pathological condition, especially in mucosal tissues such as the gastrointestinal tract and respiratory tract.