Dietary cholesterol reverses resistance to diet-induced weight gain in mice lacking Niemann-Pick C1-Like 1

Niemann-Pick C1-Like 1 (NPC1L1) mediates intestinal cholesterol absorption. NPC1L1 knockout (L1-KO) mice were recently shown to be resistant to high-fat diet (HFD)-induced obesity in one study, which was contrary to several other studies. Careful comparison of dietary compositions in these studies implies a potential role of dietary cholesterol in regulating weight gain. To examine this potential, wild-type (WT) and L1-KO mice were fed one of three sets of diets for various durations: (1) a HFD without added cholesterol for 5 weeks; (2) a high-carbohydrate diet with or without added cholesterol for 5 weeks; or (3) a synthetic HFD with or without added cholesterol for 18 weeks. We found that L1-KO mice were protected against diet-induced weight gain only on a diet without added cholesterol but not on a diet containing 0.16% or 0.2% (w/w) cholesterol, an amount similar to a typical Western diet, regardless of the major energy source of the diet. Food intake and intestinal fat absorption were similar between the two genotypes. Intestinal cholesterol absorption was blocked, and fecal cholesterol excretion increased in L1-KO mice. Under all diets, L1-KO mice were protected from hepatosteatosis. In conclusion, increasing dietary cholesterol restores diet-induced weight gain in mice deficient in NPC1L1-dependent cholesterol absorption.     

A retrospective evaluation of the role of T cells in the development of malaria vaccine

Due to the fact that the life cycle of malaria parasites is complex, undergoing both an extracellular and intracellular phases in its host, the human immune system has to mobilize both the humoral and cellular arms of immune responses to fight against this parasitic infection. Whereas humoral immunity is directed toward the extracellular stages which include sporozoites and merozoites, cell-mediated immunity (CMI), in which T cells play a major role, targets hepatic stages - liver stages - of the parasites. In this review, the role of T cells in protective immunity against liver stages of the malaria infection is being re-evaluated. Furthermore, this review intends to address how to translate the findings regarding the role of T cells obtained in experimental systems to actual development of malaria vaccine for humans.     

Identification and characterization of associated with lipid droplet protein 1: A novel membrane-associated protein that resides on hepatic lipid droplets

Alcoholic and nonalcoholic liver steatosis and steatohepatitis are characterized by the massive accumulation of lipid droplets (LDs) in the cytosol of hepatocytes. Although LDs are ubiquitous and dynamic organelles found in the cells of a wide range of organisms, little is known about the mechanisms and sites of LD biogenesis. To examine the participation of these organelles in the pathophysiological disorders of steatotic livers, we used a combination of mass spectrometry (matrix-assisted laser desorption ionization-time of flight and LC-MS electrospray) and Western blot analysis to study the composition of LDs purified from rat liver after a partial hepatectomy. Fifty proteins were identified. Adipose differentiation-related protein was the most abundant, but other proteins such as calreticulin, TIP47, Sar1, Rab GTPases, Rho and actin were also found. In addition, we identified protein associated with lipid droplets I ALDI (tentatively named Associated with LD protein 1), a novel protein widely expressed in liver and kidney corresponding to the product of 0610006F02Rik (GI:27229118). Our results show that, upon lipid loading of the cells, ALDI translocates from the endoplasmic reticulum into nascent LDs and indicate that ALDI may be targeted to the initial lipid deposits that eventually form these droplets. Moreover, we used ALDI expression studies to view other processes related to these droplets, such as LD biogenesis, and to analyze LD dynamics. In conclusion, here we report the composition of hepatic LDs and describe a novel bona fide LD-associated protein that may provide new insights into the mechanisms and sites of LD biogenesis.     

Association of the -112A>C polymorphism of the uncoupling protein 1 gene with insulin resistance in Japanese individuals with type 2 diabetes

The -112A>C polymorphism (rs10011540) of the gene for uncoupling protein 1 (UCP1) has been associated with type 2 diabetes mellitus in Japanese individuals. The aim of the present study was to investigate the effects of this polymorphism, as well as the well-known -3826A>G polymorphism (rs1800592), on clinical characteristics of type 2 diabetes. We determined the genotypes of the two polymorphisms in 93 Japanese patients with type 2 diabetes. Intramyocellular lipid content and hepatic lipid content (HLC) were measured by magnetic resonance spectroscopy. No significant differences in age, sex, BMI, or HbA1c level were detected between type 2 diabetic patients with the -112C allele and those without it. However, homeostasis model assessment for insulin resistance (p=0.0089) and HLC (p=0.012) was significantly greater in patients with the -112C allele. We did not detect an association of the -3826A>G polymorphism (rs1800592) of UCP1 gene with any measured parameters. These results suggest that insulin resistance caused by the -112C allele influences the susceptibility to type 2 diabetes.     

Targeted overexpression of inducible 6-phosphofructo-2-kinase in adipose tissue increases fat deposition but protects against diet-induced insulin resistance and inflammatory responses

Increasing evidence demonstrates the dissociation of fat deposition, the inflammatory response, and insulin resistance in the development of obesity-related metabolic diseases. As a regulatory enzyme of glycolysis, inducible 6-phosphofructo-2-kinase (iPFK2, encoded by PFKFB3) protects against diet-induced adipose tissue inflammatory response and systemic insulin resistance independently of adiposity. Using aP2-PFKFB3 transgenic (Tg) mice, we explored the ability of targeted adipocyte PFKFB3/iPFK2 overexpression to modulate diet-induced inflammatory responses and insulin resistance arising from fat deposition in both adipose and liver tissues. Compared with wild-type littermates (controls) on a high fat diet (HFD), Tg mice exhibited increased adiposity, decreased adipose inflammatory response, and improved insulin sensitivity. In a parallel pattern, HFD-fed Tg mice showed increased hepatic steatosis, decreased liver inflammatory response, and improved liver insulin sensitivity compared with controls. In both adipose and liver tissues, increased fat deposition was associated with lipid profile alterations characterized by an increase in palmitoleate. Additionally, plasma lipid profiles also displayed an increase in palmitoleate in HFD-Tg mice compared with controls. In cultured 3T3-L1 adipocytes, overexpression of PFKFB3/iPFK2 recapitulated metabolic and inflammatory changes observed in adipose tissue of Tg mice. Upon treatment with conditioned medium from iPFK2-overexpressing adipocytes, mouse primary hepatocytes displayed metabolic and inflammatory responses that were similar to those observed in livers of Tg mice. Together, these data demonstrate a unique role for PFKFB3/iPFK2 in adipocytes with regard to diet-induced inflammatory responses in both adipose and liver tissues.     

Severe hepatocellular disease in mice lacking one or both CaaX prenyltransferases

Protein farnesyltransferase (FTase) and protein geranylgeranyltransferase-I (GGTase-I) add 15- or 20-carbon lipids, respectively, to proteins that terminate with a CaaX motif. These posttranslational modifications of proteins with lipids promote protein interactions with membrane surfaces in cells, but the in vivo importance of the CaaX prenyltransferases and the protein lipidation reactions they catalyze remain incompletely defined. One study concluded that a deficiency of FTase was inconsequential in adult mice and led to little or no tissue pathology. To assess the physiologic importance of the CaaX prenyltransferases, we used conditional knockout alleles and an albumin-Cre transgene to produce mice lacking FTase, GGTase-I, or both enzymes in hepatocytes. The hepatocyte-specific FTase knockout mice survived but exhibited hepatocellular disease and elevated transaminases. Mice lacking GGTase-I not only had elevated transaminases but also had dilated bile cannaliculi, hyperbilirubinemia, hepatosplenomegaly, and reduced survival. Of note, GGTase-I-deficient hepatocytes had a rounded shape and markedly reduced numbers of actin stress fibers. Hepatocyte-specific FTase/GGTase-I double-knockout mice closely resembled mice lacking GGTase-I alone, but the disease was slightly more severe. Our studies refute the notion that FTase is dispensable and demonstrate that GGTase-I is crucial for the vitality of hepatocytes.     

AMP-activated protein kinase: an emerging drug target to regulate imbalances in lipid and carbohydrate metabolism to treat cardio-metabolic diseases: Thematic Review Series: New Lipid and Lipoprotein Targets for the Treatment of Cardiometabolic Diseases

The adenosine monophosphate-activated protein kinase (AMPK) is a metabolic sensor of energy metabolism at the cellular as well as whole-body level. It is activated by low energy status that triggers a switch from ATP-consuming anabolic pathways to ATP-producing catabolic pathways. AMPK is involved in a wide range of biological activities that normalizes lipid, glucose, and energy imbalances. These pathways are dysregulated in patients with metabolic syndrome (MetS), which represents a clustering of major cardiovascular risk factors including diabetes, lipid abnormalities, and energy imbalances. Clearly, there is an unmet medical need to find a molecule to treat alarming number of patients with MetS. AMPK, with multifaceted activities in various tissues, has emerged as an attractive drug target to manage lipid and glucose abnormalities and maintain energy homeostasis. A number of AMPK activators have been tested in preclinical models, but many of them have yet to reach to the clinic. This review focuses on the structure-function and role of AMPK in lipid, carbohydrate, and energy metabolism. The mode of action of AMPK activators, mechanism of anti-inflammatory activities, and preclinical and clinical findings as well as future prospects of AMPK as a drug target in treating cardio-metabolic disease are discussed.     

Lipidomic analysis of lipid droplets from murine hepatocytes reveals distinct signatures for nutritional stress

Liver steatosis can be induced by fasting or high-fat diet. We investigated by lipidomic analysis whether such metabolic states are reflected in the lipidome of hepatocyte lipid droplets (LDs) from mice fed normal chow diet (FED), fasted (FAS), or fed a high-fat diet (HFD). LC-MS/MS at levels of lipid species profiles and of lipid molecular species uncovered a FAS phenotype of LD enriched in triacylglycerol (TG) molecular species with very long-chain (VLC)-PUFA residues and an HFD phenotype with less unsaturated TG species in addition to characteristic lipid marker species. Nutritional stress did not result in dramatic structural alterations in diacylglycerol (DG) and phospholipid (PL) classes. Moreover, molecular species of bulk TG and of DG indicated concomitant de novo TG synthesis and lipase-catalyzed degradation to be active in LDs. DG species with VLC-PUFA residues would be preferred precursors for phosphatidylcholine (PC) species, the others for TG molecular species. In addition, molecular species of PL classes fitted the hepatocyte Kennedy and phosphatidylethanolamine methyltransferase pathways. We demonstrate that lipidomic analysis of LDs enables phenotyping of nutritional stress. TG species are best suited for such phenotyping, whereas structural analysis of TG, DG, and PL molecular species provides metabolic insights.