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Naked mole-rats are extraordinarily long-lived rodents that offer unique opportunities to study the molecular origins of age-related neurodegenerative diseases. Remarkably, they do not accumulate amyloid plaques, even though their brains contain high concentrations of amyloid beta (Aβ) peptide from a young age. Therefore, they represent a particularly favourable organism to study the mechanisms of resistance against Aβ neurotoxicity. Here we examine the composition, phase behaviour, and Aβ interactions of naked mole-rat brain lipids. Relative to mouse, naked mole-rat brain lipids are rich in cholesterol and contain sphingomyelin in lower amounts and of shorter chain lengths. Proteins associated with the metabolism of ceramides, sphingomyelins and sphingosine-1-phosphate receptor 1 were also found to be decreased in naked mole-rat brain lysates. Correspondingly, we find that naked mole-rat brain lipid membranes exhibit a high degree of phase separation, with the liquid ordered phase extending to 80% of the supported lipid bilayer. These observations are consistent with the 'membrane pacemaker' hypothesis of ageing, according to which long-living species have lipid membranes particularly resistant to oxidative damage. We also found that exposure to Aβ disrupts naked mole-rat brain lipid membranes significantly, breaking the membrane into pieces while mouse brain derived lipids remain largely intact upon Aβ exposure.

Introduction Intestinal epithelial barrier (IEB) integrity plays a central role in the pathogenesis of inflammatory bowel disease (IBD). There is a growing interest in dietary compounds that can strengthen IEB. First, candidate strains of dairy propionic bacteria such as Propionibacterium freudenreichii are able to reduce inflammation and improve barrier strength. Knowing that certain products of omega-6 polyunsaturated fatty acid (n-6 PUFA) metabolism also reinforce IEB, and that bacteria can modulate the bioavailability of host lipid compounds, this project aims to identify strains of P. freudenreichii that could protect against colitis by strengthening IEB and increasing the bioavailability of certain n-6 PUFA. MethodsA screening of thirty-three strains of P. freudenreichii was performed based on the following criteria: 1) characterization of the ability to induce production of anti-inflammatory cytokines (IL-10) by stimulation of human PBMCs 2) identification of surface proteins (S-layer protein) responsible for anti-inflammatory properties 3) measurement of their ability to increase the bioavailability of certain n-6 PUFAs, such as conjugated linoleic acids (CLAs). The ability of the selected fermented products to prevent the inflammation-induced increase in permeability of an IEB was then studied. ResultsAll strains are able to induce IL-10 production and release CLAs. Ten strains show an anti-inflammatory S-layer profile. Some fermented products significantly prevent the inflammation-induced increase in permeability, and may involve surface proteins and bioactive lipids. DiscussionThese results will allow the selection of strains with anti-inflammatory as well as pro-repair potential to be tested in vivo to reduce colitis, with or without n-6 PUFA supplementation.

International audience; L’intégrité de la barrière épithéliale intestinale (BEI) joue un rôle central dans la pathogenèse des maladies inflammatoires chroniques de l’intestin (MICI). Un intérêt grandissant est porté aux composés alimentaires capables de renforcer ou de restaurer la BEI. C’est le cas de souches de Propionibacterium freudenreichii, une bactérie propionique laitière, capable de restaurer la BEI fragilisée dans un contexte inflammatoire. Egalement, il existe une protection locale de la BEI exercée par les produits du métabolisme des acides gras polyinsaturés oméga-6 (AGPI n-6) par les cellules intestinales. Les omégas 6 sont apportés par l’alimentation, dont le lait. Les enzymes de leur métabolisme sont sous-exprimés chez les patients atteints de MICI, empêchant l’action bénéfique d’une supplémentation en AGPI n-6 chez ces patients. L’augmentation de la biodisponibilité des dérivés AGPI n-6 reste une piste intéressante. Par ailleurs, certaines souches de P. freudenreichii, sont capables de convertir l’acide linoléique, un AGPI n-6, en acide linoléique conjugué (ALC), capable de prévenir des colites induites chez des souris. Ces souches pourraient donc moduler la biodisponibilité et le métabolisme des AGPI n-6. Notre objectif vise à rechercher des effets additifs voire synergiques entre l’effet de 1) P. freudenreichii et 2) des AGPI n-6 sur la BEI. Un criblage de trente-trois souches de P. freudenreichii a été réalisé basé sur les critères suivants : 1) caractérisation de la capacité à induire la production de cytokines anti-inflammatoire (IL-10) par stimulation de PBMCs humaines 2) identification de protéines de surface (S-layer protein) responsable des propriétés anti-inflammatoire par une technique de rasage enzymatique suivis d’une identification par MS/MS 3) mesure de l’activité lipolytique dans la matière grasse laitière et de la conversion de l’acide linoléique en ALC avec une identification des lipides par GC-MS. Toutes les souches sont capables d’induire la production d’IL-10. Seulement, la puissance d’induction d’IL-10 est souche dépendante. Sur les trente-trois souches, dix présentent un profil S-layer anti-inflammatoire. Toutes les souches sont capables de lipolyser la matière grasse laitière, certaines produisent de l’acide linoléique. Toutes les souches exceptées une, sont capable de convertir l’acide linoléique en ALC. De façon similaire aux profils des cytokines, la production d’ALC est souche dépendante. Ces résultats apportent de nouvelles connaissances sur P. freudenreichii, et vont permettre sélectionner des souches qui, ayant un potentiel anti-inflammatoire ainsi que pro-réparateur, seront testées in vivo pour réduire la colite, avec ou sans supplémentation en AGPI n-6.

Mucosal CD4+ T lymphocytes display a potent opioid-mediated analgesic activity in interleukin (IL)-10 knockout mouse model of inflammatory bowel diseases (IBD). Considering that endogenous opioids may also exhibit anti-inflammatory activities in the periphery, we examined the consequences of a peripheral opioid receptor blockade by naloxone-methiodide, a general opioid receptor antagonist unable to cross the blood–brain barrier, on the development of piroxicam-accelerated colitis in IL-10-deficient (IL-10-/-) mice. Here, we show that IL-10-deficient mice treated with piroxicam exhibited significant alterations of the intestinal barrier function, including permeability, inflammation-related bioactive lipid mediators, and mucosal CD4+ T lymphocyte subsets. Opioid receptor antagonization in the periphery had virtually no effect on colitis severity but significantly worsened epithelial cell apoptosis and intestinal permeability. Thus, although the endogenous opioid tone is not sufficient to reduce the severity of colitis significantly, it substantially contributes to the protection of the physical integrity of the epithelial barrier.

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder that is characterized by chronic abdominal pain concurrent with altered bowel habit. Polyunsaturated fatty acid (PUFA) metabolites are increased in abundance in IBS and are implicated in the alteration of sensation to mechanical stimuli, which is defined as visceral hypersensitivity. We sought to quantify PUFA metabolites in patients with IBS and evaluate their role in pain. Quantification of PUFA metabolites by mass spectrometry in colonic biopsies showed an increased abundance of 5-oxoeicosatetraenoic acid (5-oxoETE) only in biopsies taken from patients with IBS with predominant constipation (IBS-C). Local administration of 5-oxoETE to mice induced somatic and visceral hypersensitivity to mechanical stimuli without causing tissue inflammation. We found that 5-oxoETE directly acted on both human and mouse sensory neurons as shown by lumbar splanchnic nerve recordings and Ca2+ imaging of dorsal root ganglion (DRG) neurons. We showed that 5-oxoETE selectively stimulated nonpeptidergic, isolectin B4 (IB4)-positive DRG neurons through a phospholipase C (PLC)- and pertussis toxin-dependent mechanism, suggesting that the effect was mediated by a G protein-coupled receptor (GPCR). The MAS-related GPCR D (Mrgprd) was found in mouse colonic DRG afferents and was identified as being implicated in the noxious effects of 5-oxoETE. Together, these data suggest that 5-oxoETE, a potential biomarker of IBS-C, induces somatic and visceral hyperalgesia without inflammation in an Mrgprd-dependent manner. Thus, 5-oxoETE may play a pivotal role in the abdominal pain associated with IBS-C.