Harnessing the Vnn1 pantetheinase pathway boosts short chain fatty acids production and mucosal protection in colitis.

OBJECTIVE: In the management of patients with IBD, there is a need to identify prognostic markers and druggable biological pathways to improve mucosal repair and probe the efficacy of tumour necrosis factor alpha biologics. Vnn1 is a pantetheinase that degrades pantetheine to pantothenate (vitamin B5, a precursor of coenzyme A (CoA) biosynthesis) and cysteamine. Vnn1 is overexpressed by inflamed colonocytes. We investigated its contribution to the tolerance of the intestinal mucosa to colitis-induced injury. DESIGN: We performed an RNA sequencing study on colon biopsy samples from patients with IBD stratified according to clinical severity and modalities of treatment. We generated the VIVA mouse transgenic model, which specifically overexpresses Vnn1 on intestinal epithelial cells and explored its susceptibility to colitis. We developed a pharmacological mimicry of Vnn1 overexpression by administration of Vnn1 derivatives. RESULTS: VNN1 overexpression on colonocytes correlates with IBD severity. VIVA mice are resistant to experimentally induced colitis. The pantetheinase activity of Vnn1 is cytoprotective in colon: it enhances CoA regeneration and metabolic adaptation of colonocytes; it favours microbiota-dependent production of short chain fatty acids and mostly butyrate, shown to regulate mucosal energetics and to be reduced in patients with IBD. This prohealing phenotype is recapitulated by treating control mice with the substrate (pantethine) or the products of pantetheinase activity prior to induction of colitis. In severe IBD, the protection conferred by the high induction of VNN1 might be compromised because its enzymatic activity may be limited by lack of available substrates. In addition, we identify the elevation of indoxyl sulfate in urine as a biomarker of Vnn1 overexpression, also detected in patients with IBD. CONCLUSION: The induction of Vnn1/VNN1 during colitis in mouse and human is a compensatory mechanism to reinforce the mucosal barrier. Therefore, enhancement of vitamin B5-driven metabolism should improve mucosal healing and might increase the efficacy of anti-inflammatory therapy.

Embryonic macrophages function during early life to determine invariant natural killer T cell levels at barrier surfaces.

It is increasingly recognized that immune development within mucosal tissues is under the control of environmental factors during early life. However, the cellular mechanisms that underlie such temporally and regionally restrictive governance of these processes are unclear. Here, we uncover an extrathymic pathway of immune development within the colon that is controlled by embryonic but not bone marrow-derived macrophages, which determines the ability of these organs to receive invariant natural killer T (iNKT) cells and allow them to establish local residency. Consequently, early-life perturbations of fetal-derived macrophages result in persistent decreases of mucosal iNKT cells and is associated with later-life susceptibility or resistance to iNKT cell-associated mucosal disorders. These studies uncover a host developmental program orchestrated by ontogenically distinct macrophages that is regulated by microbiota, and they reveal an important postnatal function of macrophages that emerge in fetal life.

Epithelial endoplasmic reticulum stress orchestrates a protective IgA response.

Immunoglobulin A (IgA) is the major secretory immunoglobulin isotype found at mucosal surfaces, where it regulates microbial commensalism and excludes luminal factors from contacting intestinal epithelial cells (IECs). IgA is induced by both T cell-dependent and -independent (TI) pathways. However, little is known about TI regulation. We report that IEC endoplasmic reticulum (ER) stress induces a polyreactive IgA response, which is protective against enteric inflammation. IEC ER stress causes TI and microbiota-independent expansion and activation of peritoneal B1b cells, which culminates in increased lamina propria and luminal IgA. Increased numbers of IgA-producing plasma cells were observed in healthy humans with defective autophagy, who are known to exhibit IEC ER stress. Upon ER stress, IECs communicate signals to the peritoneum that induce a barrier-protective TI IgA response.

Vnn1 pantetheinase limits the Warburg effect and sarcoma growth by rescuing mitochondrial activity.

Like other tumors, aggressive soft tissue sarcomas (STS) use glycolysis rather than mitochondrial oxidative phosphorylation (OXPHOS) for growth. Given the importance of the cofactor coenzyme A (CoA) in energy metabolism, we investigated the impact of Vnn1 pantetheinase-an enzyme that degrades pantetheine into pantothenate (vitamin B5, the CoA biosynthetic precursor) and cysyteamine-on tumor growth. Using two models, we show that Vnn1+ STS remain differentiated and grow slowly, and that in patients a detectable level of VNN1 expression in STS is associated with an improved prognosis. Increasing pantetheinase activity in aggressive tumors limits their growth. Using combined approaches, we demonstrate that Vnn1 permits restoration of CoA pools, thereby maintaining OXPHOS. The simultaneous production of cysteamine limits glycolysis and release of lactate, resulting in a partial inhibition of STS growth in vitro and in vivo. We propose that the Warburg effect observed in aggressive STS is reversed by induction of Vnn1 pantetheinase and the rewiring of cellular energy metabolism by its products.

Dietary and Microbial Oxazoles Induce Intestinal Inflammation by Modulating Aryl Hydrocarbon Receptor Responses.

Genome-wide association studies have identified risk loci associated with the development of inflammatory bowel disease, while epidemiological studies have emphasized that pathogenesis likely involves host interactions with environmental elements whose source and structure need to be defined. Here, we identify a class of compounds derived from dietary, microbial, and industrial sources that are characterized by the presence of a five-membered oxazole ring and induce CD1d-dependent intestinal inflammation. We observe that minimal oxazole structures modulate natural killer T cell-dependent inflammation by regulating lipid antigen presentation by CD1d on intestinal epithelial cells (IECs). CD1d-restricted production of interleukin 10 by IECs is limited through activity of the aryl hydrocarbon receptor (AhR) pathway in response to oxazole induction of tryptophan metabolites. As such, the depletion of the AhR in the intestinal epithelium abrogates oxazole-induced inflammation. In summary, we identify environmentally derived oxazoles as triggers of CD1d-dependent intestinal inflammatory responses that occur via activation of the AhR in the intestinal epithelium.

CD1d-Restricted pathways in hepatocytes control local natural killer T cell homeostasis and hepatic inflammation.

Invariant natural killer T (iNKT) cells recognize lipid antigens presented by CD1d and play a central role in regulating immunity and inflammation in peripheral tissues. However, the mechanisms which govern iNKT cell homeostasis after thymic emigration are incompletely understood. Here we demonstrate that microsomal triglyceride transfer protein (MTP), a protein involved in the transfer of lipids onto CD1d, regulates liver iNKT cell homeostasis in a manner dependent on hepatocyte CD1d. Mice with hepatocyte-specific loss of MTP exhibit defects in the function of CD1d and show increased hepatic iNKT cell numbers as a consequence of altered iNKT cell apoptosis. Similar findings were made in mice with hepatocyte-specific loss of CD1d, confirming a critical role of CD1d in this process. Moreover, increased hepatic iNKT cell abundance in the absence of MTP is associated with susceptibility to severe iNKT cell-mediated hepatitis, thus demonstrating the importance of CD1d-dependent control of liver iNKT cells in maintaining immunological homeostasis in the liver. Together, these data demonstrate an unanticipated role of parenchymal cells, as shown here for hepatocytes, in tissue-specific regulation of CD1d-restricted immunity and further suggest that alterations in lipid metabolism may affect iNKT cell homeostasis through effects on CD1d-associated lipid antigens.

Correlation between early-life regulation of the immune system by microbiota and allergy development.

Early postnatal life is a key time for development of the immune system and colonization of the host by microbiota. Recent studies have shown that specific limbs of the immune system can be regulated by microbiota in a time-restricted period during early life. Studies in mouse models have shown that perturbations of the microbiota during early life can cause immune effects that can persist into adulthood and create increased host susceptibility to certain diseases. Here we discuss the role of early-life regulation of the immune system by the microbiota and how it can be related to allergy development.

How colonization by microbiota in early life shapes the immune system.

Microbial colonization of mucosal tissues during infancy plays an instrumental role in the development and education of the host mammalian immune system. These early-life events can have long-standing consequences: facilitating tolerance to environmental exposures or contributing to the development of disease in later life, including inflammatory bowel disease, allergy, and asthma. Recent studies have begun to define a critical period during early development in which disruption of optimal host-commensal interactions can lead to persistent and in some cases irreversible defects in the development and training of specific immune subsets. Here, we discuss the role of early-life education of the immune system during this "window of opportunity," when microbial colonization has a potentially critical impact on human health and disease.

Sox17 regulates liver lipid metabolism and adaptation to fasting.

Liver is a major regulator of lipid metabolism and adaptation to fasting, a process involving PPARalpha activation. We recently showed that the Vnn1 gene is a PPARalpha target gene in liver and that release of the Vanin-1 pantetheinase in serum is a biomarker of PPARalpha activation. Here we set up a screen to identify new regulators of adaptation to fasting using the serum Vanin-1 as a marker of PPARalpha activation. Mutagenized mice were screened for low serum Vanin-1 expression. Functional interactions with PPARalpha were investigated by combining transcriptomic, biochemical and metabolic approaches. We characterized a new mutant mouse in which hepatic and serum expression of Vanin-1 is depressed. This mouse carries a mutation in the HMG domain of the Sox17 transcription factor. Mutant mice display a metabolic phenotype featuring lipid abnormalities and inefficient adaptation to fasting. Upon fasting, a fraction of the PPARα-driven transcriptional program is no longer induced and associated with impaired fatty acid oxidation. The transcriptional phenotype is partially observed in heterozygous Sox17+/- mice. In mutant mice, the fasting phenotype but not all transcriptomic signature is rescued by the administration of the PPARalpha agonist fenofibrate. These results identify a novel role for Sox17 in adult liver as a modulator of the metabolic adaptation to fasting.

PPARalpha regulates the production of serum Vanin-1 by liver.

The membrane-bound Vanin-1 pantetheinase regulates tissue adaptation to stress. We investigated Vnn1 expression and its regulation in liver. Vnn1 is expressed by centrolobular hepatocytes. Using novel tools, we identify a soluble form of Vnn1 in mouse and human serum and show the contribution of a cysteine to its catalytic activity. We show that liver contributes to Vanin-1 secretion in serum and that PPARalpha is a limiting factor in serum Vnn1 production. Functional PPRE sites are identified in the Vnn1 promoter. These results indicate that serum Vnn1 might be a reliable reporter of PPARalpha activity in liver.

Functional polymorphisms in the regulatory regions of the VNN1 gene are associated with susceptibility to inflammatory bowel diseases.

BACKGROUND: Vanin-1 is an epithelial pantetheinase, which regulates intestinal inflammation in mouse. We investigated whether human VNN1 levels could be associated to the susceptibility to inflammatory bowel diseases (IBD) and explored the participation of PPARg to these processes. METHODS: We studied VNN1 expression in colon biopsies from IBD patients. We investigated polymorphisms in the regulatory regions of the VNN1 gene and examined their genetic association with the disease. Functional relevance of these single-nucleotide polymorphisms (SNPs) was assayed, and we tested PPARg in nuclear complexes associated with specific VNN1 polymorphic sequences. In mouse, we examined Vanin-1 expression in gut and feces during dextran sulfate sodium-induced colitis and assayed the effect of PPARg on Vanin-1 regulation. RESULTS: VNN1 is expressed by enterocytes and is upregulated in IBD. Three SNPs are statistically associated to IBD. The regions containing these SNPs specifically bind nuclear complexes and are correlated with the VNN1 transcript abundance in colon in an allele-dependent manner. One rare SNP is associated to severe ulcerative colitis with strong VNN1 and dropped PPARg levels. PPARg is involved in nuclear complexes that bound to VNN1 regulatory sites. Similarly, Vanin-1 is tightly regulated in the mouse gut in normal and colitis conditions and PPARg regulates its expression. CONCLUSIONS: VNN1 is a marker for IBD. Polymorphic positions in the VNN1 locus are direct targets for nuclear factors that might regulate the level of VNN1 in colon, and this could be linked to IBD susceptibility. It is hoped that modulating locally VNN1 expression or activity can be exploited to develop future therapeutic strategies against IBD.