(ISTAP and expert group co-chairs) EXPERT WORKING GROUP Kimberly LeBlanc, Canada (co-chair of working group) Karen Campbell, Canada (co-chair of working group

Sphingosine kinase 1 (SK1) phosphorylates sphingosine to generate sphingosine 1-phosphate (S1P). Because both substrate and product of the enzyme are potentially important signaling molecules, the regulation of SK1 is of considerable interest. We report that SK1, which is ordinarily a cytosolic enzyme, translocates in vivo and in vitro to membrane compartments enriched in phosphatidic acid (PA), the lipid product of phospholipase D. This translocation depends on direct interaction of SK1 with PA, because recombinant purified enzyme shows strong affinity for pure PA coupled to Affi-Gel. The SK1-PA interaction maps to the C terminus of SK1 and is independent of catalytic activity or of the diacylglycerol kinaselike domain of the enzyme. Thus SK1 constitutes a novel, physiologically relevant PA effector.The potential function of PA 1 in signal transduction is not well established, and there is even debate about whether PA itself (or a downstream metabolite) is a signaling lipid (1). Whereas many cellular control pathways exhibit a stimulusdependent elevation of PLD activity (arguing for a direct role of the lipid product of PLD-PA in these pathways (2)), historically, the search for classic protein effectors of PA has failed to yield many clear-cut examples where a specific response to elevated PA levels could be demonstrated directly.Recent data from a number of laboratories are beginning to define some potential PA targets. These include kinases (e.g. Raf-1 (3, 4) and mammalian target of rapamycin (5)), phosphatases (e.g. protein-tyrosine phosphatase SHP-1 (6) and protein phosphatase-1 (7)), enzymes involved in lipid turnover (e.g. phosphatidylinositol-4-phosphate 5-kinase (8, 9) and phospholipase C (10)), as well as other enzymes (e.g. phosphodiesterase PDE4D3 (11, 12)). There are additional examples of proteins regulated by PA in combination with other lipids (e.g. protein kinase C⑀ (13) and p47phox (14)). With the possible exception of Raf-1 and PKC⑀, regulation of the other proteins by PA has not been shown to result directly in membrane translocation in vivo. Raf-1 accumulates in endosomal membranes as a consequence of PA formation (4), whereas PKC⑀ translocates to the plasma membrane in response to coordinated production of PA and diacylglycerol (13).By phosphorylating sphingosine to generate S1P, SK1 regulates the levels of two important bioactive lipids and affects a number of cellular functions, including for example calcium mobilization, growth control, and cytoskeletal rearrangements among others (for a recent review see Ref. 15). We became interested in the possibility that SK1 may constitute a novel PA effector based on three types of evidence. SK1 activity is stimulated by acidic phospholipids, including PA (16), it is found up-regulated in immune cells following PLD activation (reviewed in Ref. 17), and the SK1 protein is activated by PKC (a PLD activator) and translocates to membranes following stimulation with phorbol esters (18).In this work we show that SK1 is a PA effector and responds to PA f...

Background Aronia melanocarpa is a rich source of (poly)phenols. Previous research has demonstrated that these berries may provide cardiovascular health benefits in high-risk populations. However, very few studies have investigated the effects of daily consumption of dietary achievable amounts of the berries in healthy subjects. Objectives The aim of this study was to investigate the effects of aronia berries on vascular function and gut microbiota composition in a healthy population. Methods A double-blind, placebo-controlled, parallel designed study was conducted in 66 healthy men randomly allocated to consume a (poly)phenol-rich extract (116 mg, 75 g berries), a whole fruit powder (12 mg, 10 g berries), or placebo (maltodextrin) for 12 wk. Flow-mediated dilation (FMD), arterial stiffness, blood pressure, heart rate, and serum biochemistry were assessed. Plasma (poly)phenol metabolites were analyzed by LC-MS. Gut microbiota composition was determined via 16S rRNA sequencing in stool samples. Results Consumption of aronia whole fruit and extract powder for 12 wk led to a significant increase in FMD over control of 0.9% ± 0.4% (95% CI: 0.13%, 1.72%) and 1.2% ± 0.4% (95% CI: 0.36%, 1.97%), respectively. Acute improvements in FMD were also observed 2 h after consumption of aronia extract on day 1 (1.1% ± 0.3%, P = 0.003) and 12 wk later (1.5% ± 0.4%, P = 0.0001). Circulating plasma phenolic metabolites increased upon consumption of the aronia treatments. Although no changes were found in gut microbiota diversity, consumption of aronia extract increased the growth of Anaerostipes (+10.6%, P = 0.01), whereas aronia whole fruit showed significant increases in Bacteroides (+193%, P = 0.01). Correlation analysis identified significant associations between changes in FMD, aronia-derived phenolic metabolites, and specific gut microbial genera. Conclusions In healthy men, consumption of aronia berry (poly)phenols improved endothelial function and modulated gut microbiota composition, indicating that regular aronia consumption has the potential to maintain cardiovascular health in individuals at low risk of cardiovascular disease. This trial was registered at CLINICALTRIALs.gov as NCT03041961.

Phosphatidic acid (PA) is postulated to have both structural and signaling functions during membrane dynamics in animal cells. In this study, we show that before a critical time period during rhabdomere biogenesis in Drosophila melanogaster photoreceptors, elevated levels of PA disrupt membrane transport to the apical domain. Lipidomic analysis shows that this effect is associated with an increase in the abundance of a single, relatively minor molecular species of PA. These transport defects are dependent on the activation state of Arf1. Transport defects via PA generated by phospholipase D require the activity of type I phosphatidylinositol (PI) 4 phosphate 5 kinase, are phenocopied by knockdown of PI 4 kinase, and are associated with normal endoplasmic reticulum to Golgi transport. We propose that PA levels are critical for apical membrane transport events required for rhabdomere biogenesis.

Phospholipase D (PLD) hydrolyses phosphatidylcholine into phosphatidic acid (PA) and choline. Our work aims to understand the properties of PLD1, and to identify downstream targets of PA. In one set of projects, we have focused on membrane-targeting mechanisms and have proposed a hierarchy of signals that allows PLD1 to localize to intracellular membranes. These signals involve a functional pleckstrin homology (PH) domain and its fatty acylation on two adjacent cysteine residues. A nearby Phox homology (PX) domain may modulate the function of the fatty acylated PH domain. This complex array of signals is probably necessitated by the targeting of PLD1 to multiple endocytic and secretory membranes under basal and signal-dependent conditions. In another set of projects, we have used chemically synthesized PA coupled to a solid support in order to identify proteins that interact with this phospholipid. Several proteins have emerged from this screen as potential targets. Some (e.g. ADP-ribosylation factor, coatomer β subunit) are involved in trafficking and their PA affinity can be understood in terms of their regulated cycling on and off membranes during rounds of transport. Others (sphingosine 1-phosphate kinase and PtdIns4P 5-kinase) are implicated in pathways that also involve PLD activation. Others still are novel proteins (brain-specific neurochondrin) whose affinity for PA may contribute to an understanding of their cellular function.

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ObjectiveThe short isoform of thymic stromal lymphopoietin (TSLP), a cytokine constitutively expressed by epithelial cells, is crucial in preserving immune tolerance in the gut. TSLP deficiency has been implicated in sustaining intestinal damage in Crohn's disease. We explored mucosal TSLP expression and function in refractory and uncomplicated coeliac disease (CD), a T-cell-mediated enteropathy induced by gluten in genetically susceptible individuals.DesignTSLP isoforms—long and short—and receptors—TSLPR and interleukin (IL)-7Rα—were assessed by immunofluorescence, immunoblotting and qRT-PCR in the duodenum of untreated, treated, potential and refractory patients with CD. The ability of the serine protease furin or CD biopsy supernatants to cleave TSLP was evaluated by immunoblotting. The production of interferon (IFN)-γ and IL-8 by untreated CD biopsies cultured ex vivo with TSLP isoforms was also assessed.ResultsMucosal TSLP, but not TSLPR and IL-7Rα, was reduced in untreated CD and refractory CD in comparison to treated CD, potential CD and controls. Transcripts of both TSLP isoforms were decreased in active CD mucosa. Furin, which was overexpressed in active CD biopsies, was able to cleave TSLP in vitro. Accordingly, refractory and untreated CD supernatants showed higher TSLP-degrading capacity in comparison to treated CD and control supernatants. In our ex vivo model, both TSLP isoforms significantly downregulated IFN-γ and IL-8 production by untreated CD biopsies.ConclusionsReduced mucosal TSLP expression may contribute to intestinal damage in refractory and untreated CD. Further studies are needed to verify whether restoring TSLP might be therapeutically useful especially in refractory patients with CD.