Mucosal protection by phosphatidylcholine

The colonic mucus serves a first barrier towards invasion of commensal bacteria in stools to prevent inflammation. One essential component of intestinal mucus is phosphatidylcholine (PC) which represents more than 90% of the phospholipids in mucus indicative for a selective transport of PC into this compartment. It is arranged in lamellar structures as surfactant-like particles which provide a hydrophobic surface on top of the hydrated mucus gel to prevent the invasion of bacteria from intestinal lumen. In ulcerative colitis (UC), the mucus PC content is reduced by 70%, irrespective of the state of inflammation. Thus, it could represent an intrinsic primary pathogenetic condition predisposing to bacterial invasion and the precipitation of inflammation. Since PC was shown to be mainly secreted by the ileal mucosa from where it is assumed to move distally to the colon, the PC content along the colonic wall towards the rectum gradually thins, with the least PC content in the rectum. This explains the start of the clinical manifestation of UC in the rectum and the expansion from there to the upper parts of the colon. In three clinical trials, when missing mucus PC in UC was supplemented by an oral, delayed release PC preparation, the inflammation improved and even resolved after a 3-month treatment course. The data indicate the essential role of the mucus PC content for protection against inflammation in colon. Copyright (C) 2012 S. Karger AG, Base

Group VIA phospholipase A2 deficiency in mice chronically fed with high-fat-diet attenuates hepatic steatosis by correcting a defect of phospholipid remodeling

A defect of hepatic remodeling of phospholipids (PL) is seen in non-alcoholic fatty liver disease and steatohepatitis (NASH) indicating pivotal role of PL metabolism in this disease. The deletion of group VIA calcium independent phospholipase A2 (iPla2 beta) protects ob/ob mice from hepatic steatosis (BBAIip 1861, 2016, 440-461), however its role in high-fat diet (HFD)-induced NASH is still elusive. Here, wild-type and iPla2 beta-null mice were subjected to chronic feeding with HFD for 6 months. We showed that protection was observed in iPla2 beta-null mice with an attenuation of diet-induced body and liver-weight gains, liver enzymes, serum free fatty acids as well as hepatic TG and steatosis scores. iPla2 beta deficiency under HFD attenuated the levels of 1-stearoyl lysophosphatidylcholine (LPC), lysophosphatidylethanolamine (LPE), and lysophosphatidylinositol (LPI) as well as elevation of hepatic arachidonate, arachidonate-containing cholesterol esters and prostaglandin E-2. More importantly, this deficiency rescued a defect in PL remodeling and attenuated the ratio of saturated and unsaturated PL. The protection by iPla2 beta deficiency was not observed during short-term HFD feeding of 3 or 5 weeks which showed no PL remodeling defect. In addition to PC/PE, this deficiency reversed the suppression of PC/PI and PE/PI among monounsaturated PL. However, this deficiency did not modulate hepatic PL contents and PL ratios in ER fractions, ER stress, fibrosis, and inflammation markers. Hence, iPla2 beta inactivation protected mice against hepatic steatosis and obesity during chronic dietary NASH by correcting PL remodeling defect and PI composition relative to PC and PE

Constitutive oxidants from hepatocytes of male iPLA2β-null mice increases the externalization of phosphatidylethanolamine on plasma membrane

We have found that group VIA calcium-independent phospholipase A2 (iPLA2 beta) has specificity for hydrolysis of phosphatidylethanolamine (PE) in mouse livers. Phospholipids (PLs) are transported to plasma membrane and some PLs including PE are externalized to maintain membrane PL asymmetry. Here we demonstrated that hepatocytes of iPLA2 beta-null (KO) mice showed an increase in PE containing palmitate and oleate. We aimed to examine whether externalization of PE on the outer leaflets could be affected by iPLA2 beta deficiency and its modulation by reactive oxygen species (ROS) or apoptosis. As duramycin has high affinity to PE, we used duramycin conjugated with biotin (DLB) and streptavidin 488 as a probe for detection of externalized PE. Compared to WT, naive KO hepatocytes showed an increase in both PE externalization and ROS generation. These events were observed in male but not in female KO mice. Hydrogen peroxide or menadione treatment enhanced PE externalization to the same extent for both male/female WT and KO hepatocytes. By indirect immunofluorescence, DLB-streptavidin staining was observed as small punctuated spots on the cell surface of menadione-treated KO hepatocytes. Unlike the reported PS externalization, CD95/FasL treatment did not lead to any increase in PE externalization, and iPLA2 beta deficiency-dependent PE externalization was also not correlated with apoptosis. Thus, constitutive (but not induced) ROS generation in iPLA2 beta-deficient hepatocytes leads to PE externalization observed only in male mice. Such PE externalization may imply detrimental effects regarding further oxidation of PE fatty acids and the binding with pathogens on the outer leaflets of hepatocyte plasma membrane

iPla2β deficiency in mice fed with MCD diet does not correct the defect of phospholipid remodeling but attenuates hepatocellular injury via an inhibition of lipid uptake genes

Group VIA calcium-independent phospholipase A2 (iPla2 beta) is among modifier genes of non-alcoholic fatty liver disease which leads to non-alcoholic steatohepatitis (NASH). Consistently, iPla2 beta deletion protects hepatic steatosis and obesity in genetic ob/ob and obese mice chronically fed with high-fat diet by replenishing the loss of hepatic phospholipids (PL). As mouse feeding with methionine- and choline-deficient (MCD) diet is a model of lean NASH, we tested whether iPla2 beta-null mice could still be protected since PL syntheses are disturbed. MCD-diet feeding of female wild-type for 5 weeks induced hepatic steatosis with a severe reduction of body and visceral fat weights concomitant with a decrease of hepatic phosphatidylcholine. These parameters were not altered in MCD-fed iPla2 beta-null mice. However, iPla2 beta deficiency attenuated MCD-induced elevation of serum transaminase activities and hepatic expression of fatty-acid translocase Cd36, fatty-acid binding protein-4, peroxisome-proliferator activated receptor gamma, and HDL-uptake scavenger receptor B type 1. The reduction of lipid uptake genes was consistent with a decrease of hepatic esterified and unesterified fatty acids and cholesterol esters. On the contrary, iPla2 beta deficiency under MCD did not have any effects on inflammasomes and proinflammatory markers but exacerbated hepatic expression of myofibroblast a-smooth muscle actin and vimentin. Thus, without any rescue of PL loss, iPla2 beta inactivation attenuated hepatocellular injury in MCD-induced NASH with a novel mechanism of lipid uptake inhibition. Taken together, we have shown that iPla2 beta mediates hepatic steatosis and lipotoxicity in hepatocytes in both obese and lean NASH, but elicits exacerbated liver fibrosis in lean NASH likely by affecting other cell types

Methionine- and Choline-Deficient Diet Enhances AdiposeLipolysis and Leptin Release in aP2-Cre Fatp4-Knockout Mice

Scope Inadequate intake of choline commonly leads to liver diseases. Methionine‐ and choline‐deficient diets (MCDD) induce fatty liver in mice which is partly mediated by triglyceride (TG) lipolysis in white adipose tissues (WATs). Because Fatp4 knockdown has been shown to increase adipocyte lipolysis in vitro, here, the effects of MCDD on WAT lipolysis in aP2‐Cre Fatp4‐knockout (Fatp4A−/−) mice are determined. Methods and Results Isolated WATs of Fatp4A−/− mice exposed to MCD medium show an increase in lipolysis, and the strongest effect is noted on glycerol release from subcutaneous fat. Fatp4A−/− mice fed with MCDD for 4 weeks show an increase in serum glycerol, TG, and leptin levels associated with the activation of hormone‐sensitive lipase in subcutaneous fat. Chow‐fed Fatp4A−/− mice also show an increase in serum leptin and very‐low‐density lipoproteins as well as liver phosphatidylcholine and sphingomyelin levels. Both chow‐ and MCDD‐fed Fatp4A−/− mice show a decrease in serum ketone and WAT sphingomyelin levels which supports a metabolic shift to TG for subsequent WAT lipolysis Conclusions Adipose Fatp4 deficiency leads to TG lipolysis and leptin release, which are exaggerated by MCDD. The data imply hyperlipidemia risk by a low dietary choline intake and gene mutations that increase adipose TG levels