Phosphatidylcholine protects against steatosis in mice but not non-alcoholic steatohepatitis
ABSTRACT Several studies suggest that low levels of hepatic phosphatidylcholine (PC) play a role in the pathogenesis of non-alcoholic steatohepatitis (NASH). CTP: phosphocholine cytidylyltransferase (CT) is the key regulatory enzyme in the CDP-choline pathway for PC biosynthesis. Liver-specific elimination of CTα (LCTα(-/-)) in mice fed a chow diet decreases very-low-density lipoprotein secretion, reduces lipid efflux from liver, and causes mild steatosis. We fed LCTα(-/-) mice a high fat diet to determine if impaired PC biosynthesis played a role in development of NASH. LCTα(-/-) mice developed NASH within one week of high fat feeding. Hepatic CTα deficiency caused hepatic steatosis, a 2-fold increase in ceramide mass, and a 20% reduction in PC content. In an attempt to prevent NASH, LCTα(-/-) mice were either injected daily with CDP-choline or fed the high fat diet supplemented with betaine. In addition, LCTα(-/-) mice were injected with adenoviruses expressing CTα. CDP-choline injections and adenoviral expression of CTα increased hepatic PC, while dietary betaine supplementation normalized hepatic triacylglycerol but did not alter hepatic PC mass in LCTα(-/-) mice. Interestingly, none of the treatments normalized hepatic ceramide mass or fully prevented the development of NASH in LCTα(-/-) mice. These results show that normalizing the amount of hepatic PC is not sufficient to prevent NASH in LCTα(-/-) mice.
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ABSTRACT: Steatohepatitis (SH) is an intermediate stage of fatty liver disease and one of the most common causes of chronic liver disease worldwide that may progress to cirrhosis and liver cancer. SH encompasses alcoholic and nonalcoholic steatohepatitis, the latter being of particular concern due to its association with obesity and insulin resistance and a major cause of liver transplantation. The molecular mechanisms governing the transition from steatosis to SH are not fully understood. Here we discuss emerging data indicating that acid sphingomyelinase (ASMase), a specific mechanism of ceramide generation, is required for the activation of key pathways that regulate steatosis, fibrosis and lipotoxicity, including endoplasmic reticulum stress, autophagy and lysosomal membrane permeabilization. Moreover, ASMase modulates alterations of methionine cycle and phosphatidylcholine homeostasis, two crucial events involved in SH that regulate methylation reactions, antioxidant defense and membrane integrity. These new findings suggest that targeting ASMase in combination with restoration of methionine metabolism and phosphatidylcholine levels may be of utility in the treatment of SH.Journal of Hepatology 10/2014; 62(1). DOI:10.1016/j.jhep.2014.09.023 · 10.40 Impact Factor
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ABSTRACT: Soybean-derived PC is an essential cell membrane phospholipid that is composed of unsaturated fatty acids, including oleic acid. The present study aimed to evaluate the potential alleviation effects of soybean PC on high fat diet (HFD)-induced obesity and its related complications.Life Sciences 10/2014; DOI:10.1016/j.lfs.2014.09.027 · 2.30 Impact Factor
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ABSTRACT: During invasion, Plasmodium, the causative agent of malaria, wraps itself in a parasitophorous vacuole membrane (PVM), which constitutes a critical interface between the parasite and its host cell. Within hepatocytes, each Plasmodium sporozoite generates thousands of new parasites, creating high demand for lipids to support this replication and enlarge the PVM. Here, a global analysis of the total lipid repertoire of Plasmodium-infected hepatocytes reveals an enrichment of neutral lipids and the major membrane phospholipid, phosphatidylcholine (PC). While infection is unaffected in mice deficient in key enzymes involved in neutral lipid synthesis and lipolysis, ablation of rate-limiting enzymes in hepatic PC biosynthetic pathways significantly decreases parasite numbers. Host PC is taken up by both P. berghei and P. falciparum and is necessary for correct localization of parasite proteins to the PVM, which is essential for parasite survival. Thus, Plasmodium relies on the abundance of these lipids within hepatocytes to support infection.Cell Host & Microbe 12/2014; 16(6):778. DOI:10.1016/j.chom.2014.11.006 · 12.19 Impact Factor