Lipoprotein lipase and hepatic lipase mRNA tissue specific expression, developmental regulation, and evolution

Development of an Improved Adenovirus Vector and Its Application to the Treatment of Lifestyle-Related Diseases

The number of patients with lifestyle-related diseases such as type 2 diabetes mellitus (T2DM) and metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD), has continued to increase worldwide. Therefore, development of innovative therapeutic methods targeting lifestyle-related diseases is required. Gene therapy has attracted considerable attention as an advanced medical treatment. Safe and high-performance vectors are essential for the practical application of gene therapy. Replication-incompetent adenovirus (Ad) vectors are widely used in clinical gene therapy and basic research. Here, we developed a novel Ad vector, named Ad-E4-122aT, exhibiting higher and longer-term transgene expression and lower hepatotoxicity than conventional Ad vectors. We also elucidated the mechanisms underlying Ad vector-induced hepatotoxicity during the early phase using Ad-E4-122aT. Next, we examined the therapeutic effects of the genes of interest, namely zinc finger AN1-type domain 3 (ZFAND3), lipoprotein lipase (LPL), and lysophospholipid acyltransferase 10 (LPLAT10), on lifestyle-related diseases using Ad-E4-122aT. We showed that the overexpression of ZFAND3 in the liver improved glucose tolerance and insulin resistance. Liver-specific LPL overexpression suppressed hepatic lipid accumulation and improved glucose metabolism. LPLAT10 overexpression in the liver suppressed postprandial hyperglycemia by increasing glucose-stimulated insulin secretion. Furthermore, we also focused on foods to advance research on the pathophysiology and treatment of lifestyle-related diseases. Cranberry and calamondin, which are promising functional foods, attenuated the progression of MASLD/NAFLD. Our findings will aid the development of new therapeutic methods, including gene therapy, for lifestyle-related diseases such as T2DM and MASLD/NAFLD.

The response to fasting and refeeding reveals functional regulation of lipoprotein lipase proteoforms

Lipoprotein lipase (LPL) is responsible for the intravascular catabolism of triglyceride-rich lipoproteins and plays a central role in whole-body energy balance and lipid homeostasis. As such, LPL is subject to tissue-specific regulation in different physiological conditions, but the mechanisms of this regulation remain incompletely characterized. Previous work revealed that LPL comprises a set of proteoforms with different isoelectric points, but their regulation and functional significance have not been studied thus far. Here we studied the distribution of LPL proteoforms in different rat tissues and their regulation under physiological conditions. First, analysis by two-dimensional electrophoresis and Western blot showed different patterns of LPL proteoforms (i.e., different pI or relative abundance of LPL proteoforms) in different rat tissues under basal conditions, which could be related to the tissue-specific regulation of the enzyme. Next, the comparison of LPL proteoforms from heart and brown adipose tissue between adults and 15-day-old rat pups, two conditions with minimal regulation of LPL in these tissues, yielded virtually the same tissue-specific patterns of LPL proteoforms. In contrast, the pronounced downregulation of LPL activity observed in white adipose tissue during fasting is accompanied by a prominent reconfiguration of the LPL proteoform pattern. Furthermore, refeeding reverts this downregulation of LPL activity and restores the pattern of LPL proteoforms in this tissue. Importantly, this reversible proteoform-specific regulation during fasting and refeeding indicates that LPL proteoforms are functionally diverse. Further investigation of potential differences in the functional properties of LPL proteoforms showed that all proteoforms exhibit lipolytic activity and have similar heparin-binding affinity, although other functional aspects remain to be investigated. Overall, this study demonstrates the ubiquity, differential distribution and specific regulation of LPL proteoforms in rat tissues and underscores the need to consider the existence of LPL proteoforms for a complete understanding of LPL regulation under physiological conditions.

Lipoprotein lipase concentration in umbilical cord blood reflects neonatal birth weight

BACKGROUND

Insulin resistance (IR) is exacerbated during pregnancy via increases in insulin counterregulatory hormones. Maternal lipids are strong determinants of neonatal growth, although triglyceride-rich lipoproteins (TGRLs) cannot be transferred directly to the fetus through the placenta. The catabolism of TGRLs under physiological IR and the reduced synthesis of lipoprotein lipase (LPL) are poorly understood. We examined the association of maternal and umbilical cord blood (UCB)-LPL concentrations with maternal metabolic parameters and fetal development.

METHODS

Changes in anthropometric measures and lipid-, glucose-, and insulin-related parameters, including maternal and UCB-LPL concentrations, were examined in 69 women during pregnancy. The relationship between those parameters and neonatal birth weight was assessed.

RESULTS

Parameters reflecting glucose metabolism did not change during pregnancy, whereas those associated with lipid metabolism and IR changed markedly, particularly in the second and third trimesters. In the third trimester, the maternal LPL concentration gradually decreased, by 54%, whereas the UCB-LPL concentration was ∼2-fold higher than the maternal LPL concentration. Univariate and multivariate analyses showed that the UCB-LPL concentration was a significant determinant of neonatal birth weight, together with placental birth weight.

CONCLUSION

The LPL concentration in UCB reflects neonatal development under a decreased LPL concentration in maternal serum.

The Regulation of Triacylglycerol Metabolism and Lipoprotein Lipase Activity

Triacylglycerol (TG) metabolism is tightly regulated to maintain a pool of TG within circulating lipoproteins that can be hydrolyzed in a tissue-specific manner by lipoprotein lipase (LPL) to enable the delivery of fatty acids to adipose or oxidative tissues as needed. Elevated serum TG concentrations, which result from a deficiency of LPL activity or, more commonly, an imbalance in the regulation of tissue-specific LPL activities, have been associated with an increased risk of atherosclerotic cardiovascular disease through multiple studies. Among the most critical LPL regulators are the angiopoietin-like (ANGPTL) proteins ANGPTL3, ANGPTL4, and ANGPTL8, and a number of different apolipoproteins including apolipoprotein A5 (ApoA5), apolipoprotein C2 (ApoC2), and apolipoprotein C3 (ApoC3). These ANGPTLs and apolipoproteins work together to orchestrate LPL activity and therefore play pivotal roles in TG partitioning, hydrolysis, and utilization. This review summarizes the mechanisms of action, epidemiological findings, and genetic data most relevant to these ANGPTLs and apolipoproteins. The interplay between these important regulators of TG metabolism in both fasted and fed states is highlighted with a holistic view toward understanding key concepts and interactions. Strategies for developing safe and effective therapeutics to reduce circulating TG by selectively targeting these ANGPTLs and apolipoproteins are also discussed.

Liver-specific overexpression of lipoprotein lipase improves glucose metabolism in high-fat diet-fed mice

The liver is the main organ that regulates lipid and glucose metabolism. Ectopic lipid accumulation in the liver impairs insulin sensitivity and glucose metabolism. Lipoprotein lipase (LPL), mainly expressed in the adipose tissue and muscle, is a key enzyme that regulates lipid metabolism via the hydrolysis of triglyceride in chylomicrons and very-low-density lipoproteins. Here, we aimed to investigate whether the suppression level of hepatic lipid accumulation via overexpression of LPL in mouse liver leads to improved metabolism. To overexpress LPL in the liver, we generated an LPL-expressing adenovirus (Ad) vector using an improved Ad vector that exhibited considerably lower hepatotoxicity (Ad-LPL). C57BL/6 mice were treated with Ad vectors and simultaneously fed a high-fat diet (HFD). Lipid droplet formation in the liver decreased in Ad-LPL-treated mice relative to that in control Ad vector-treated mice. Glucose tolerance and insulin resistance were remarkably improved in Ad-LPL-treated mice compared to those in control Ad vector-treated mice. The expression levels of fatty acid oxidation-related genes, such as peroxisome proliferator-activated receptor α, carnitine palmitoyltransferase 1, and acyl-CoA oxidase 1, were 1.7–2.0-fold higher in Ad-LPL-treated mouse livers than that in control Ad-vector-treated mouse livers. Furthermore, hepatic LPL overexpression partly maintained mitochondrial content in HFD-fed mice. These results indicate that LPL overexpression in the livers of HFD-fed mice attenuates the accumulation of lipid droplets in the liver and improves glucose metabolism. These findings may enable the development of new drugs to treat metabolic syndromes such as type 2 diabetes mellitus and non-alcoholic fatty liver disease.

Characterization of lipoprotein lipase storage vesicles in 3T3-L1 adipocytes

Lipoprotein lipase (LPL) is a secreted triglyceride lipase involved in the clearance of very-low-density lipoproteins and chylomicrons from circulation. LPL is expressed primarily in adipose and muscle tissues and transported to the capillary lumen. LPL secretion is regulated by insulin in adipose tissue; however, few studies have examined the regulatory and trafficking steps involved in secretion. Here, we describe the intracellular localization and insulin-dependent trafficking of LPL in 3T3-L1 adipocytes. We compared LPL trafficking to the better characterized trafficking pathways taken by leptin and GLUT4 (also known as SLC2A4). We show that the LPL trafficking pathway shares some characteristics of these other pathways, but that LPL subcellular localization and trafficking are distinct from those of GLUT4 and leptin. LPL secretion occurs slowly in response to insulin and rapidly in response to the Ca2+ ionophore ionomycin. This regulated trafficking is dependent on Golgi protein kinase D and the ADP-ribosylation factor GTPase ARF1. Together, these data give support to a new trafficking pathway for soluble cargo that is active in adipocytes.

Regulation of lipoprotein metabolism by ANGPTL3, ANGPTL4, and ANGPTL8

Triglyceride-rich lipoproteins deliver fatty acids to tissues for oxidation and for storage. Release of fatty acids from circulating lipoprotein triglycerides is carried out by lipoprotein lipase (LPL), thus LPL serves as a critical gatekeeper of fatty acid uptake into tissues. LPL activity is regulated by a number of extracellular proteins including three members of the angiopoietin-like family of proteins. In this review, we discuss our current understanding of how, where, and when ANGPTL3, ANGPTL4, and ANGPTL8 regulate lipoprotein lipase activity, with a particular emphasis on how these proteins interact with each other to coordinate triglyceride metabolism and fat partitioning.

Advances in fatty acids nutrition in dairy cows: from gut to cells and effects on performance

High producing dairy cows generally receive in the diet up to 5-6% of fat. This is a relatively low amount of fat in the diet compared to diets in monogastrics; however, dietary fat is important for dairy cows as demonstrated by the benefits of supplementing cows with various fatty acids (FA). Several FA are highly bioactive, especially by affecting the transcriptome; thus, they have nutrigenomic effects. In the present review, we provide an up-to-date understanding of the utilization of FA by dairy cows including the main processes affecting FA in the rumen, molecular aspects of the absorption of FA by the gut, synthesis, secretion, and utilization of chylomicrons; uptake and metabolism of FA by peripheral tissues, with a main emphasis on the liver, and main transcription factors regulated by FA. Most of the advances in FA utilization by rumen microorganisms and intestinal absorption of FA in dairy cows were made before the end of the last century with little information generated afterwards. However, large advances on the molecular aspects of intestinal absorption and cellular uptake of FA were made on monogastric species in the last 20 years. We provide a model of FA utilization in dairy cows by using information generated in monogastrics and enriching it with data produced in dairy cows. We also reviewed the latest studies on the effects of dietary FA on milk yield, milk fatty acid composition, reproduction, and health in dairy cows. The reviewed data revealed a complex picture with the FA being active in each step of the way, starting from influencing rumen microbiota, regulating intestinal absorption, and affecting cellular uptake and utilization by peripheral tissues, making prediction on in vivo nutrigenomic effects of FA challenging.

Research Progress on the Involvement of ANGPTL4 and Loss-of-Function Variants in Lipid Metabolism and Coronary Heart Disease: Is the "Prime Time" of ANGPTL4-Targeted Therapy for Coronary Heart Disease Approaching?

BACKGROUND

Multiple genetic studies have confirmed the definitive link among the loss-of-function variants of angiogenin-like protein 4 (ANGPTL4), significantly decreased plasma triglyceride (TG) levels, and reduced risk of coronary heart disease (CHD). The potential therapeutic effect of ANGPTL4 on dyslipidemia and CHD has been widely studied.

OBJECTIVE

This review provides a detailed introduction to the research progress on the involvement of ANGPTL4 in lipid metabolism and atherosclerosis and evaluates the efficacy and safety of ANGPTL4 as a therapeutic target for CHD.

RELEVANT FINDINGS

By inhibiting lipoprotein lipase (LPL) activity, ANGPTL4 plays a vital role in the regulation of lipid metabolism and energy balance. However, the role of ANGPTL4 in regulating lipid metabolism is tissue-specific. ANGPTL4 acts as a locally released LPL inhibitor in the heart, skeletal muscle and small intestine, while ANGPTL4 derived from liver and adipose tissue mainly acts as an endocrine factor that regulates systemic lipid metabolism. As a multifunctional protein, ANGPTL4 also inhibits the formation of foam cells in macrophages, exerting an anti-atherogenic role. The function of ANGPTL4 in endothelial cells is still uncertain. The safety of ANGPTL4 monoclonal antibodies requires further evaluation due to their potential adverse effects.

CONCLUSION

The biological characteristics of ANGPTL4 are much more complex than those demonstrated by genetic studies. Future studies must elucidate how to effectively reduce the risk of CHD while avoiding potential atherogenic effects and other complications before the "prime time" of ANGPTL4-targeted therapy arrives.

ANGPTL4 in Metabolic and Cardiovascular Disease

Alterations in circulating lipids and ectopic lipid deposition impact on the risk of developing cardiovascular and metabolic diseases. Lipoprotein lipase (LPL) hydrolyzes fatty acids (FAs) from triglyceride (TAG)-rich lipoproteins including very low density lipoproteins (VLDLs) and chylomicrons, and regulates their distribution to peripheral tissues. Angiopoietin-like 4 (ANGPTL4) mediates the inhibition of LPL activity under different circumstances. Accumulating evidence associates ANGPTL4 directly with the risk of atherosclerosis and type 2 diabetes (T2D). This review focuses on recent findings on the role of ANGPTL4 in metabolic and cardiovascular diseases. We highlight human and murine studies that explore ANGPTL4 functions in different tissues and how these effect disease development through possible autocrine and paracrine forms of regulation.

Arabinoxylan activates lipid catabolism and alleviates liver damage in rats induced by high-fat diet

BACKGROUND

Arabinoxylan was thought to have the potential to change lipid metabolism and redox homeostasis in human and animal. However, the effect of arabinoxylan on the liver damage induced by high-fat diet needs further exploiting.

RESULTS

Six-weeks-old 30 male Sprague-Dawley Rats were assigned randomly to three groups (n = 10 per group), i.e. a control diet (CON) group, a high-fat diet (HF) group and a high-fat diet supplemented with arabinoxylan (6% AX, HF-AX) group. Results showed that final body weight and liver weight were similar in CON group and HF-AX group, but higher in the HF group. In serum, the HF-AX group showed lower triglyceride concentrations than did the HF group. In liver, higher lipoprotein lipase, hepatic lipase, total lipase, and acyl-CoA oxidase activities and lower triglyceride and cholesterol level were observed in the HF-AX group than in the HF group. For the redox homeostasis, arabinoxylan supplemented in HF increased T-SOD activity and GSH-PX activity and reduced MDA + 4-HNE level in liver and/or compared with those in the HF group. Lipid droplets and liver cell damage were observed in the HF group compared with the CON and HF-AX groups.

CONCLUSION

Arabinoxylan could improve lipid metabolic disorder and alleviate liver damage in rats induced by high-fat diet via activating lipid catabolism and suppressing lipid peroxidation. © 2017 Society of Chemical Industry.

Chylomicrons: Advances in biology, pathology, laboratory testing, and therapeutics

The adequate absorption of lipids is essential for all mammalian species due to their inability to synthesize some essential fatty acids and fat-soluble vitamins. Chylomicrons (CMs) are large, triglyceride-rich lipoproteins that are produced in intestinal enterocytes in response to fat ingestion, which function to transport the ingested lipids to different tissues. In addition to the contribution of CMs to postprandial lipemia, their remnants, the degradation products following lipolysis by lipoprotein lipase, are linked to cardiovascular disease. In this review, we will focus on the structure-function and metabolism of CMs. Second, we will analyze the impact of gene defects reported to affect CM metabolism and, also, the role of CMs in other pathologies, such as atherothrombotic cardiovascular disease and diabetes mellitus. Third, we will provide an overview of the laboratory tests currently used to study CM disorders, and, finally, we will highlight current treatments in diseases affecting CMs.

Fish oil diet in pregnancy and lactation reduces pup weight and modifies newborn hepatic metabolic adaptations in rats

PURPOSE

To determine the effects of a diet containing fish oil (FD) during pregnancy and lactation in rats on the metabolic adaptations made by the offspring during early extrauterine life and to compare it to an olive oil diet (OD).

METHODS

Rats were mated and randomly allocated to OD or FD containing 10 % of the corresponding oil. During lactation, litters were adjusted to eight pups per dam. Fetuses of 20 days and pups of 0, 1, 10, 20 and 30 days of age were studied.

RESULTS

Body weight and length were lower in pups of the FD group from birth. The diet, milk, pups' plasma and liver of FD group had higher proportions of n-3 LCPUFA, but the content of arachidonic acid (ARA) was lower. Plasma glucose was higher, but unesterified fatty acids, triacylglycerols (TAG), 3-hydroxybutyrate and liver TAG in 1-day-old pups were lower in the FD group, and differences in some of these variables were also found in pups up to 30 days old. Liver lipoprotein lipase activity and mRNA expression, and the expression of carnitine palmitoyl transferase I, acyl-CoA oxidase and 3-hydroxy 3-methyl glutaryl-CoA synthase increased more at birth in pups of the FD group, but the expression of sterol regulatory element binding protein-1c and Δ6-desaturase mRNA was lower in the FD group.

CONCLUSIONS

Maternal intake of high n-3 LCPUFA retards postnatal development, which could be the result of impaired ARA synthesis, and affects hepatic metabolic adaptations to extrauterine life.

Hepatocyte β-Klotho regulates lipid homeostasis but not body weight in mice

β-Klotho (β-Kl), a transmembrane protein expressed in the liver, pancreas, adipose tissues, and brain, is essential for feedback suppression of hepatic bile acid synthesis. Because bile acid is a key regulator of lipid and energy metabolism, we hypothesized potential and tissue-specific roles of β-Kl in regulating plasma lipid levels and body weight. By crossing β-kl(-/-) mice with newly developed hepatocyte-specific β-kl transgenic (Tg) mice, we generated mice expressing β-kl solely in hepatocytes (β-kl(-/-)/Tg). Gene expression, metabolomic, and in vivo flux analyses consistently revealed that plasma level of cholesterol, which is over-excreted into feces as bile acids in β-kl(-/-), is maintained in β-kl(-/-) mice by enhanced de novo cholesterogenesis. No compensatory increase in lipogenesis was observed, despite markedly decreased plasma triglyceride. Along with enhanced bile acid synthesis, these lipid dysregulations in β-kl(-/-) were completely reversed in β-kl(-/-)/Tg mice. In contrast, reduced body weight and resistance to diet-induced obesity in β-kl(-/-) mice were not reversed by hepatocyte-specific restoration of β-Kl expression. We conclude that β-Kl in hepatocytes is necessary and sufficient for lipid homeostasis, whereas nonhepatic β-Kl regulates energy metabolism. We further demonstrate that in a condition with excessive cholesterol disposal, a robust compensatory mechanism maintains cholesterol levels but not triglyceride levels in mice.

The modulating effect of Persea americana fruit extract on the level of expression of fatty acid synthase complex, lipoprotein lipase, fibroblast growth factor-21 and leptin--A biochemical study in rats subjected to experimental hyperlipidemia and obesity

BACKGROUND

Obesity is a multifactorial disorder which is closely associated with hyperlipidemia. Avocados are edible fruits traditionally consumed for various health benefits including body weight reduction.

HYPOTHESIS/PURPOSE

To determine the hypolipidemic and anti-obesity effect of hydro-alcoholic fruit extract of avocado (HFEA) in rats fed with high fat diet (HFD).

STUDY DESIGN

Male Sprague Dawley rats were divided into four groups. Groups 1 and 2 rats were fed with normal diet. Groups 3 and 4 rats were fed with HFD for 14 weeks. In addition, Groups 2 and 4 rats were co-administered with 100 mg/kg body weight of HFEA from 3rd week onwards.

METHODS

The HFEA was subjected to HPLC to quantify the major phytonutrients. Body mass index (BMI), adiposity index (ADI), total fat pad mass (TFP), blood lipid levels were determined in all the groups of rats. The mRNA expression of fatty acid synthase (FASN), lipoprotein lipase (LPL), fibroblast growth factor 21 (FGF21) and leptin was also assessed.

RESULTS

HFEA was found to contain flavonoids: rutin-141.79, quercetin-5.25, luteolin-165, phenolic compounds: gallic acid-198.57, ellagic acid-238.22, vanillic acid-4.79 and phytosterols: betasitosterol-70, stigmasterol-12.5 (mg/100 g). HFEA reduced BMI, ADI, TFP, blood cholesterol, triglycerides, and LDL in rats fed with HFD. Serum leptin was found reduced in HFEA co-administered rats. The mRNA expression of FASN, LPL, and leptin in subcutaneous and visceral adipose tissue was found to be significantly reduced in HFEA co-administered rats. The gene expression of fibroblast growth factor-21 (FGF21) was found to be significantly increased in HFEA treated rats when compared to HFD control rats.

CONCLUSION

The hypolipidemic effect of HFEA may be partly due to its modulating effect on endogenous fat synthesis and adiponectin formation through the transcription factor FGF21. The results also show that avocado fruit extract has profound influence on leptin activity, which controls satiety and hunger to regulate the food intake.

Mono(2-ethylhexyl) phthalate accelerates early folliculogenesis and inhibits steroidogenesis in cultured mouse whole ovaries and antral follicles

Humans are ubiquitously exposed to di(2-ethylhexyl) phthalate (DEHP), which is an environmental toxicant present in common consumer products. DEHP potentially targets the ovary through its metabolite mono(2-ethylhexyl) phthalate (MEHP). However, the direct effects of MEHP on ovarian folliculogenesis and steroidogenesis, two processes essential for reproductive and nonreproductive health, are unknown. The present study tested the hypotheses that MEHP directly accelerates early folliculogenesis via overactivation of phosphatidylinositol 3-kinase (PI3K) signaling, a pathway that regulates primordial follicle quiescence and activation, and inhibits the synthesis of steroid hormones by decreasing steroidogenic enzyme levels. Neonatal ovaries from CD-1 mice were cultured for 6 days with vehicle control, DEHP, or MEHP (0.2-20 μg/ml) to assess the direct effects on folliculogenesis and PI3K signaling. Further, antral follicles from adult CD-1 mice were cultured with vehicle control or MEHP (0.1-10 μg/ml) for 24-96 h to establish the temporal effects of MEHP on steroid hormones and steroidogenic enzymes. In the neonatal ovaries, MEHP, but not DEHP, decreased phosphatase and tensin homolog levels and increased phosphorylated protein kinase B levels, leading to a decrease in the percentage of germ cells and an increase in the percentage of primary follicles. In the antral follicles, MEHP decreased the mRNA levels of 17alpha-hydroxylase-17,20-desmolase, 17beta-hydroxysteroid dehydrogenase, and aromatase leading to a decrease in testosterone, estrone, and estradiol levels. Collectively, MEHP mediates the effect of DEHP on accelerated folliculogenesis via overactivating PI3K signaling and inhibits steroidogenesis by decreasing steroidogenic enzyme levels.

Study of Protein Biomarkers of Diabetes Mellitus Type 2 and Therapy with Vitamin B1

In the present research work, the levels of protein biomarkers specific to diabetes mellitus type 2 in the Pakistani population using proteomic technology have been identified and characterized and effect of high dose thiamine has been seen on the levels of these marker proteins. Diabetic patients and normal healthy controls were recruited from the Sheikh Zayed Hospital, Lahore, Pakistan. Total biochemical assays and proteins were estimated by modern proteomic techniques. Some proteins were up- and downregulated in diabetic samples as compared to control and decreased after thiamine therapy, while other protein markers did not show a significant change after the thiamine therapy. The effect of high dose thiamine on the levels of these identified protein biomarkers in the human urine has also been observed. Assessment of the levels of these biomarkers will be helpful in not only early diagnosis but also prognosis of diabetes mellitus type 2.

Embryonic viability, lipase deficiency, hypertriglyceridemia and neonatal lethality in a novel LMF1-deficient mouse model

Background

Lipase Maturation Factor 1 (LMF1) is an ER-chaperone involved in the post-translational maturation and catalytic activation of vascular lipases including lipoprotein lipase (LPL), hepatic lipase (HL) and endothelial lipase (EL). Mutations in LMF1 are associated with lipase deficiency and severe hypertriglyceridemia indicating the critical role of LMF1 in plasma lipid homeostasis. The currently available mouse model of LMF1 deficiency is based on a naturally occurring truncating mutation, combined lipase deficiency (cld), which may represent a hypomorphic allele. Thus, development of LMF1-null mice is needed to explore the phenotypic consequences of complete LMF1 deficiency.

Findings

In situ hybridization and qPCR analysis in the normal mouse embryo revealed ubiquitous and high-level LMF1 expression. To investigate if LMF1 was required for embryonic viability, a novel mouse model based on a null-allele of LMF1 was generated and characterized. LMF1-/- progeny were born at Mendelian ratios and exhibited combined lipase deficiency, hypertriglyceridemia and neonatal lethality.

Conclusion

Our results raise the possibility of a previously unrecognized role for LMF1 in embryonic development, but indicate that LMF1 is dispensable for the viability of mouse embryo. The novel mouse model developed in this study will be useful to investigate the full phenotypic spectrum of LMF1 deficiency.

Cardiac lipotoxicity: molecular pathways and therapeutic implications

Diabetes and obesity are both associated with lipotoxic cardiomyopathy exclusive of coronary artery disease and hypertension. Lipotoxicities have become a public health concern and are responsible for a significant portion of clinical cardiac disease. These abnormalities may be the result of a toxic metabolic shift to more fatty acid and less glucose oxidation with concomitant accumulation of toxic lipids. Lipids can directly alter cellular structures and activate downstream pathways leading to toxicity. Recent data have implicated fatty acids and fatty acyl coenzyme A, diacylglycerol, and ceramide in cellular lipotoxicity, which may be caused by apoptosis, defective insulin signaling, endoplasmic reticulum stress, activation of protein kinase C, MAPK activation, or modulation of PPARs.

Lipoprotein lipase (LPL) is associated with neurite pathology and its levels are markedly reduced in the dentate gyrus of Alzheimer's disease brains

Lipoprotein lipase (LPL) is involved in regulation of fatty acid metabolism, and facilitates cellular uptake of lipoproteins, lipids and lipid-soluble vitamins. We evaluated LPL distribution in healthy and Alzheimer’s disease (AD) brain tissue and its relative levels in cerebrospinal fluid. LPL immunostaining is widely present in different neuronal subgroups, microglia, astrocytes and oligodendroglia throughout cerebrum, cerebellum and spinal cord. LPL immunoreactivity is also present in leptomeninges, small blood vessels, choroid plexus and ependymal cells, Schwann cells associated with cranial nerves, and in anterior and posterior pituitary. In vitro studies have shown presence of secreted LPL in conditioned media of human cortical neuronal cell line (HCN2) and neuroblastoma cells (SK-N-SH), but not in media of cultured primary human astrocytes. LPL was present in cytoplasmic and nuclear fractions of neuronal cells and astrocytes in vitro. LPL immunoreactivity strongly associates with AD-related pathology, staining diffuse plaques, dystrophic and swollen neurites, possible Hirano bodies and activated glial cells. We observed no staining associated with neurofibrillary tangles or granulovacuolar degeneration. Granule cells of the dentate gyrus and the associated synaptic network showed significantly reduced staining in AD compared to control tissue. LPL was also reduced in AD CSF samples relative to those in controls.

A role for hepatic leptin signaling in lipid metabolism via altered very low density lipoprotein composition and liver lipase activity in mice

Obesity is highly associated with dyslipidemia and cardiovascular disease. However, the mechanism behind this association is not completely understood. The hormone leptin may be a molecular link between obesity and dysregulation of lipid metabolism. Leptin can affect lipid metabolism independent of its well-known effects on food intake and energy expenditure, but exactly how this occurs is ill-defined. We hypothesized that since leptin receptors are found on the liver and the liver plays an integral role in regulating lipid metabolism, leptin may affect lipid metabolism by acting directly on the liver. To test this hypothesis, we generated mice with a hepatocyte-specific loss of leptin signaling. We previously showed that these mice have increased insulin sensitivity and elevated levels of liver triglycerides compared with controls. Here, we show that mice lacking hepatic leptin signaling have decreased levels of plasma apolipoprotein B yet increased levels of very low density lipoprotein (VLDL) triglycerides, suggesting alterations in triglyceride incorporation into VLDL or abnormal lipoprotein remodeling in the plasma. Indeed, lipoprotein profiles revealed larger apolipoprotein B-containing lipoprotein particles in mice with ablated liver leptin signaling. Loss of leptin signaling in the liver was also associated with a substantial increase in lipoprotein lipase activity in the liver, which may have contributed to increased lipid droplets in the liver.

CONCLUSION

Lack of hepatic leptin signaling results in increased lipid accumulation in the liver and larger, more triglyceride-rich VLDL particles. Collectively, these data reveal an interesting role for hepatic leptin signaling in modulating triglyceride metabolism.

Prognostic value of LIPC in non-small cell lung carcinoma

Non-small cell lung carcinoma (NSCLC) is the most common form of lung cancer and is associated with a high mortality rate worldwide. The majority of individuals bearing NSCLC are treated with surgery plus adjuvant cisplatin, an initially effective therapeutic regimen that, however, is unable to prevent relapse within 5 years after tumor resection in an elevated proportion of patients. The factors that predict the clinical course of NSCLC and its sensitivity to therapy remain largely obscure. One notable exception is provided by pyridoxal kinase (PDXK), the enzyme that generates the bioactive form of vitamin B6. PDXK has recently been shown to be required for optimal cisplatin responses in vitro and in vivo and to constitute a bona fide prognostic marker in the NSCLC setting. Together with PDXK, 84 additional factors were identified that influence the response of NSCLC cells to cisplatin, in vitro including the hepatic lipase LIPC. Here, we report that the intratumoral levels of LIPC, as assessed by immunohistochemistry in two independent cohorts of NSCLC patients, positively correlate with disease outcome. In one out of two cohorts studied, the overall survival of NSCLC patients bearing LIPChigh lesions was unaffected, if not slightly worsened, by cisplatin-based adjuvant therapy. Conversely, the overall survival of patients with LIPClow lesions was prolonged by post-operative cisplatin. Pending validation in appropriate clinical series, these results suggest that LIPClow NSCLC patients would be those who mainly benefit from adjuvant cisplatin therapy. Thus, the expression levels of LIPC appear to have an independent prognostic value (and perhaps a predictive potential) in the setting of NSCLC. If these findings were confirmed by additional studies, LIPC expression levels might allow not only for NSCLC patient stratification, but also for the implementation of personalized therapeutic approaches.

Atorvastatin and pitavastatin enhance lipoprotein lipase production in L6 skeletal muscle cells through activation of adenosine monophosphate-activated protein kinase

Pravastatin and atorvastatin increase the serum level of lipoprotein lipase (LPL) mass in vivo but do not increase LPL activity in 3T3-L1 preadipocytes in vitro. LPL is mainly produced by adipose tissue and skeletal muscle cells. Metformin enhances LPL in skeletal muscle through adenosine monophosphate-activated protein kinase (AMPK) activation but not in adipocytes. This study aimed to examine the effect of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) on LPL production and to investigate the mechanism by which statins enhance skeletal muscle cell LPL production. L6 skeletal muscle cells were incubated with pravastatin, simvastatin, atorvastatin or pitavastatin. LPL activity, protein levels and mRNA expression were measured. Atorvastatin and pitavastatin significantly increased LPL activity, protein levels and mRNA expression in L6 skeletal muscle cells at 1 μmol/L, but neither statin had an effect at 10 μmol/L. We measured AMPK to clarify the mechanism by which statins increase LPL production in skeletal muscle cells. At 1 μmol/L, both atorvastatin and pitavastatin enhanced AMPK activity, but this enhancement was abolished when AMPK signaling was blocked by compound C. The increased expressions of LPL protein and mRNA by atorvastatin and pitavastatin were reduced by compound C. In addition, mevalonic acid abolished atorvastatin- and pitavastatin-induced AMPK activation and LPL expression. These results suggest that atorvastatin and pitavastatin increase LPL activity, protein levels and LPL mRNA expression by activating AMPK in skeletal muscle cells.

Lipoprotein lipase as a candidate target for cancer prevention/therapy

Epidemiological studies have shown that serum triglyceride (TG) levels are linked with risk of development of cancer, including colorectal and pancreatic cancers, and their precancerous lesions. Thus, it is assumed that serum TG plays an important role in carcinogenesis, and the key enzyme lipoprotein lipase (LPL), which catalyzes the hydrolysis of plasma TG, may therefore be involved. Dysregulation of LPL has been reported to contribute to many human diseases, such as atherosclerosis, chylomicronaemia, obesity, and type 2 diabetes. Recently, it has been reported that LPL gene deficiency, such as due to chromosome 8p22 loss, LPL gene polymorphism, and epigenetic changes in its promoter region gene, increases cancer risk, especially in the prostate. In animal experiments, high serum TG levels seem to promote sporadic/carcinogen-induced genesis of colorectal and pancreatic cancers. Interestingly, tumor suppressive effects of LPL inducers, such as PPAR ligands, NO-1886, and indomethacin, have been demonstrated in animal models. Moreover, recent evidence that LPL plays important roles in inflammation and obesity implies that it is an appropriate general target for chemopreventive and chemotherapeutic agents.

Effect of starvation on activities and mRNA expression of lipoprotein lipase and hormone-sensitive lipase in tilapia (Oreochromis niloticus x O. areus)

A 4-week study was conducted to determine the effect of starvation on activities and mRNA expression of lipoprotein lipase (LPL) and hormone-sensitive lipase (HSL) in hybrid tilapia (Oreochromis niloticus x O. areus). The tissue samples were sampled once a week. Results showed that body weight (BW) and hepatosomatic index (HSI) were decreased significantly (P < 0.05) during starvation. The percentages of crude fat and crude protein in the whole body and the fat content in muscle decreased significantly (P < 0.05), while the rate of moisture and crude ash increased significantly (P < 0.05). The response of LPL, HSL activities and mRNA expression in tissues was tissue dependent. The activities of LPL and HSL in muscle at day 7 were elevated by 2.5 times (P < 0.05) and 11.8 times (P < 0.05) of the value at day 0, respectively, and both then decreased to pre-starvation levels at day 14 and finally stabilized at a certain level afterward. LPL and HSL mRNA abundance in muscle remained relatively stable between 0 and 14 day; then, a significant increase was seen after 14 days. In the liver, LPL activity maintained a significantly increasing trend during starvation, while HSL activity rose dramatically at day 7 of starvation by 2.35 times (P < 0.05) and finally stabilized at a certain level. The mRNA abundance of liver LPL increased significantly during the whole process of starvation (P < 0.05), whereas the mRNA abundance of liver HSL decreased significantly at day 7 of starvation, elevating significantly afterward (P < 0.05).

Quantitative trait locus mapping and identification of Zhx2 as a novel regulator of plasma lipid metabolism

BACKGROUND

We previously mapped a quantitative trait locus on chromosome 15 in mice contributing to high-density lipoprotein cholesterol and triglyceride levels and now report the identification of the underlying gene.

METHODS AND RESULTS

We first fine-mapped the locus by studying a series of congenic strains derived from the parental strains BALB/cJ and MRL/MpJ. Analysis of gene expression and sequencing followed by transgenic complementation led to the identification of zinc fingers and homeoboxes 2 (Zhx2), a transcription factor previously implicated in the developmental regulation of alpha-fetoprotein. Reduced expression of the protein in BALB/cJ mice resulted in altered hepatic transcript levels for several genes involved in lipoprotein metabolism. Most notably, the Zhx2 mutation resulted in a failure to suppress expression of lipoprotein lipase, a gene normally silenced in the adult liver, and this was normalized in BALB/cJ mice carrying the Zhx2 transgene.

CONCLUSIONS

We identified the gene underlying the chromosome 15 quantitative trait locus, and our results show that Zhx2 functions as a novel developmental regulator of key genes influencing lipoprotein metabolism.

Increased de novo lipogenesis in liver contributes to the augmented fat deposition in dexamethasone exposed broiler chickens (Gallus gallus domesticus)

Effect of dexamethasone (DEX, a synthetic glucocorticoid) on lipid metabolism in broiler chickens (Gallus gallus domesticus) was investigated. Male Arbor Acres chickens (1 wk old, n=30) were injected with DEX or saline for 1 wk, and a pair-fed group was included. DEX administration resulted in enhanced lipid deposition in adipose tissues. Plasma insulin increased about 3.3 fold in DEX injected chickens as against the control and hepatic triglyceride was higher as compared with the pair-fed chickens. In DEX injected chickens, the hepatic activities of malic enzyme (ME) and fatty acid synthetase (FAS) were significantly increased, while the mRNA levels of acetyl CoA carboxylase (ACC), ME, and FAS were significantly up-regulated, compared with the control. Although the mRNA levels of lipoprotein lipase (LPL), peroxisome proliferator-activated receptor-gamma (PPARgamma) and adipose triglyceride lipase (ATGL) genes in adipose tissue were not affected by DEX injection, ME activity and mRNA levels in abdominal fat pad of chickens treated with DEX are higher than those of control chickens. The results indicated that the increased hepatic de novo lipogenesis and in turn, the increased circulating lipid flux contributes to the augmented fat deposition in adipose tissues and liver in DEX-challenged chickens. The results suggest that glucocorticoids together with the induced hyperinsulinemia should be responsible for the up-regulated hepatic lipogenesis.

Genetic screening of the lipoprotein lipase gene for mutations in Chinese subjects with or without hypertriglyceridemia

OBJECTIVE

To investigate the association between the mutations in lipoprotein lipase gene and hypertriglyceridemia (HTG).

METHODS

The lipoprotein lipase (LPL) gene was screened for mutations in 386 Chinese subjects with (108 cases in the HTG group) or without HTG (278 cases in the control group), by single-strand conformation polymorphism (SSCP) analysis and DNA sequencing.

RESULTS

One novel silent mutation L103L, one missense mutation P207L, three splicing mutations Int3/3'-ass/C(-6) --> T, and the common S447X polymorphism has been identified in the whole coding region and exon-intron junctions of the LPL gene were examined. Heterozygous P207L found in the HTG group was the first case reported in Asia and subsequently another P207L heterozygote was found in the proband's family, all of which suggested that P207L was one of the causes of familial combined hyperlipidemia, but was not so prevalent as that in French Canadian. Int3/3'-ass/C(-6) --> T was found in both groups in the present study although it was regarded as a pathogenic variant to HTG earlier on. Moreover about the beneficial polymorphism S447X, there was also some supportive evidence that the levels of triglycerides (TG) in S447X carriers were significantly lower than noncarriers in the subjects without HTG.

CONCLUSIONS

The association between the LPL variants and HTG is quite complicated and versatile, genotyping of LPL in a larger-scale screening should be necessary and justifiable.

High-density lipoproteins, inflammation and oxidative stress

Plasma levels of HDL (high-density lipoprotein)-cholesterol are strongly and inversely correlated with atherosclerotic cardiovascular disease. Both clinical and epidemiological studies have reported an inverse and independent association between serum HDL-cholesterol levels and CHD (coronary heart disease) risk. The cardioprotective effects of HDLs have been attributed to several mechanisms, including their involvement in the reverse cholesterol transport pathway. HDLs also have antioxidant, anti-inflammatory and antithrombotic properties and promote endothelial repair, all of which are likely to contribute to their ability to prevent CHD. The first part of this review summarizes what is known about the origins and metabolism of HDL. We then focus on the anti-inflammatory and antioxidant properties of HDL and discuss why these characteristics are cardioprotective.

Expression of carboxylesterase and lipase genes in rat liver cell-types

Approximately 80% of the body vitamin A is stored in liver stellate cells with in the lipid droplets as retinyl esters. In low vitamin A status or after liver injury, stellate cells are depleted of the stored retinyl esters by their hydrolysis to retinol. However, the identity of retinyl ester hydrolase(s) expressed in stellate cells is unknown. The expression of carboxylesterase and lipase genes in purified liver cell-types was investigated by real-time PCR. We found that six carboxylesterase and hepatic lipase genes were expressed in hepatocytes. Adipose triglyceride lipase was expressed in Kupffer cells, stellate cells and endothelial cells. Lipoprotein lipase expression was detected in Kupffer cells and stellate cells. As a function of stellate cell activation, expression of adipose triglyceride lipase decreased by twofold and lipoprotein lipase increased by 32-fold suggesting that it may play a role in retinol ester hydrolysis during stellate cell activation.

Determination of lipoprotein lipase activity in post heparin plasma of streptozotocin-induced diabetic rats by high-performance liquid chromatography with fluorescence detection

The activity of lipoprotein lipase (LPL), an enzyme responsible for lipoprotein metabolism, would vary in diseases and metabolic disorders. For determination of LPL activity, a highly sensitive high performance liquid chromatography (HPLC) method using a fluorescent reagent, 4-nitro-7-piperazino-2,1,3-benzoxadiazole (NBD-PZ) was applied to determinate the oleic acid (OA) generated from triolein by LPL activity without multiple solvents extraction step. We studied the optimal conditions of the reaction including the effect of emulsifiers, deproteinizing solvents, and the concentration of bovine serum albumin (BSA). Ten millimolar concentrations of triolein, 5% of BSA, 1% of Gum arabic (GA), and acetonitrile showed the optimum conditions for measuring the LPL activity. The accuracy values for the determination of LPL activity in 10 microL of rat post heparin plasma were 108.73 approximately 114.36%, and the intra- and inter-day precision values were within 1.28% and 2.91%, respectively. The limit of detection was about 4.53 nM (signal-to-noise ratio 3). The proposed method was applied to determination of LPL activity in post heparin plasma of normal and streptozotocininduced diabetic rats associated with 52.3% reduction. The established assay system could be used for determining LPL activity in different physiological and pathological conditions to clarify the relationship between LPL activity and diabetes mellitus.

Comparative genomics and experimental promoter analysis reveal functional liver-specific elements in mammalian hepatic lipase genes

BACKGROUND

Mammalian hepatic lipase (HL) genes are transcribed almost exclusively in hepatocytes. The basis for this liver-restricted expression is not completely understood. We hypothesized that the responsible cis-acting elements are conserved among mammalian HL genes. To identify these elements, we made a genomic comparison of 30 kb of 5'-flanking region of the rat, mouse, rhesus monkey, and human HL genes. The in silico data were verified by promoter-reporter assays in transfected hepatoma HepG2 and non-hepatoma HeLa cells using serial 5'-deletions of the rat HL (-2287/+9) and human HL (-685/+13) promoter region.

RESULTS

Highly conserved elements were present at the proximal promoter region, and at 14 and 22 kb upstream of the transcriptional start site. Both of these upstream elements increased transcriptional activity of the human HL (-685/+13) promoter region 2-3 fold. Within the proximal HL promoter region, conserved clusters of transcription factor binding sites (TFBS) were identified at -240/-200 (module A), -80/-40 (module B), and -25/+5 (module C) by the rVista software. In HepG2 cells, modules B and C, but not module A, were important for basal transcription. Module B contains putative binding sites for hepatocyte nuclear factors HNF1alpha. In the presence of module B, transcription from the minimal HL promoter was increased 1.5-2 fold in HepG2 cells, but inhibited 2-4 fold in HeLa cells.

CONCLUSION

Our data demonstrate that searching for conserved non-coding sequences by comparative genomics is a valuable tool in identifying candidate enhancer elements. With this approach, we found two putative enhancer elements in the far upstream region of the HL gene. In addition, we obtained evidence that the -80/-40 region of the HL gene is responsible for enhanced HL promoter activity in hepatoma cells, and for silencing HL promoter activity in non-liver cells.

Dietary n-3 fatty acids affect mRNA level of brown adipose tissue uncoupling protein 1, and white adipose tissue leptin and glucose transporter 4 in the rat

We examined the effect of dietary fats rich in n-3 polyunsaturated fatty acids (PUFA) on mRNA levels in white and brown adipose tissues in rats. Four groups of rats were fed on a low-fat diet (20 g safflower oil/kg) or a high-fat diet (200 g/kg) containing safflower oil, which is rich in n-6 PUFA (linoleic acid), or perilla (α-linolenic acid) or fish oil (eicosapentaenoic and docosahexaenoic acids), both of which are rich in n-3 PUFA, for 21 d. Energy intake was higher in rats fed on a high-safflower-oil diet than in those fed on low-fat or high-fish-oil diet, but no other significant differences were detected among the groups. Perirenal white adipose tissue weight was higher and epididymal white adipose tissue weight tended to be higher in rats fed on a high-safflower-oil diet than in those fed on a low-fat diet. However, high-fat diets rich in n-3 PUFA, compared to a low-fat diet, did not increase the white adipose tissue mass. High-fat diets relative to a low-fat diet increased brown adipose tissue uncoupling protein 1 mRNA level. The increases were greater with fats rich in n-3 PUFA than with n-6 PUFA. A high-safflower-oil diet, compared to a low-fat diet, doubled the leptin mRNA level in white adipose tissue. However, high-fat diets rich in n-3 PUFA failed to increase it. Compared to a low-fat diet, high-fat diets down-regulated the glucose transporter 4 mRNA level in white adipose tissue. However, the decreases were attenuated with high-fat diets rich in n-3 PUFA. It is suggested that the alterations in gene expression in adipose tissue contribute to the physiological activities of n-3 PUFA in preventing body fat accumulation and in regulating glucose metabolism in rats.

The ASP receptor C5L2 is regulated by metabolic hormones associated with insulin resistance

Acylation-stimulating protein (ASP) and interaction with its receptor C5L2 influences adipocyte metabolism. We examined insulin resistance and differentiation-mediated regulation of C5L2 and the mechanistic impact on both C5L2 cell-surface protein and ligand binding to the receptor. C5L2 mRNA increased 8.7-fold with differentiation in 3T3-L1 cells (p < 0.0001) by day 9. In preadipocytes, insulin and dexamethasone increased C5L2 mRNA (1 μmol/L insulin resulted in a 2.6-fold increase, p < 0.01; 10 nmol/L dexamethasone resulted in a 17.9-fold increase, p < 0.01) and C5L2 cell-surface protein (100 nmol insulin resulted in a 2.7-fold increase, p < 0.001; 10 nmol/L dexamethasone resulted in a 2.8-fold increase, p < 0.001). In adipocytes, 100 nmol/L insulin increased C5L2 mRNA and ASP binding (respectively, 1.3-fold, p < 0.01; and 2.4-fold, p < 0.05). Dexamethasone decreased ligand binding (–60%, p < 0.02) without changing mRNA. Tumor necrosis factor alpha decreased C5L2 mRNA (–88% in preadipocytes and –38% in adipocytes, p < 0.001), C5L2 cell-surface protein (–53% in preadipocytes, p < 0.0001), and ASP binding (–60% and –49% in, respectively, preadipocytes and adipoctyes, p < 0.05). Conversely, 1 μmol/L and 10 nmol/L rosiglitazone increased, respectively, C5L2 mRNA (9.3-fold, p < 0.0001) and ASP binding (2.4-fold, p < 0.05). Thus, C5L2 mRNA increases with differentiation, insulin, and thiazolidinedione treatment, and decreases with tumor necrosis factor alpha, all of which results in functional changes in ASP–C5L2 response and may have implications for human metabolism.

Cloning, expression, and promoter analysis of hepatic lipase derived from human hyperplastic adrenals

Human adrenals contain hepatic lipase (HL) activity, which is thought to facilitate the uptake of plasma cholesterol used in steroidogenesis. We show here that full-length HL mRNA is expressed in hyperplastic adrenals of patients with Cushing's disease. In addition, a splice variant that lacks exon-3 was detected in the human adrenals and hepatoma (HepG2) cells, but not in liver. In CAT-reporter assays using human NCI-H295R adrenocortical cells, the HL(-685/+13) promoter region was transcriptionally active, and its activity was enhanced twofold by cAMP. In rat adrenals, the HL gene is exclusively transcribed from an alternative promoter within intron-2, resulting in a variant mRNA that lacks exons 1 and 2. By reverse-transcription PCR, we found no evidence for expression of such a variant mRNA in human adrenals, liver, or HepG2 cells. The presence of both full length mRNA and enzyme activity in human adrenals suggests that part of the HL activity is locally synthesized.

Relationship between lipoprotein lipase and peroxisome proliferator-activated receptor-α expression in rat liver during development

The present study was addressed to determine whether the high expression of peroxisome proliferator-activated receptor-alpha (PPAR-alpha) in rat liver during the perinatal stage plays a role in the induction of liver lipoprotein lipase (LPL) expression and activity. Parallel increases in liver mRNA PPAR-alpha and LPL activity were found in newborn rats, and after a slight decline, values remained elevated until weaning. Anticipated weaning for 3 days caused a decline in those two variables as well as in the mRNA LPL level, and a similar change was also found in liver triacylglycerol concentration. Force-feeding with Intralipid in 10-day-old rats or animals kept fasted for 5 h showed high mRNA-PPARalpha and -LPL levels as well as LPL activity with low plasma insulin and high FFA levels, whereas glucose and a combination of glucose and Intralipid produced low mRNA-PPARalpha and -LPL levels as well as LPL activity. Under these latter conditions, plasma insulin and FFA levels were high in those rats receiving the combination of glucose and Intralipid, whereas plasma FFA levels were low in those force-fed with glucose. It is proposed that the hormonal and nutritional induction of liver PPAR-alpha expression around birth and its maintained elevated level throughout suckling is responsible for the induction of liver LPL-expression and activity during suckling.

Concomitant suppression of hyperlipidemia and intestinal polyp formation by increasing lipoprotein lipase activity in Apc-deficient mice

Epidemiologically, a high-fat diet is associated with the risk of colon cancer. In addition, serum levels of triglycerides (TGs) and cholesterol have been demonstrated to be positively associated with colon carcinogenesis. We recently found that an age-dependent hyperlipidemic state (high serum TG levels) exists in Apc-deficient mice, an animal model for human familial adenomatous polyposis. The mRNA levels of lipoprotein lipase (LPL), which catalyzes TG hydrolysis, were shown to be downregulated in the liver and intestines of mice. Moreover, treatment with a peroxisome proliferator-activated receptor (PPAR) alpha agonist, bezafibrate, or a PPARgamma agonist, pioglitazone, suppressed both hyperlipidemia and intestinal polyp formation in the mice, with induction of LPL mRNA. PPARalpha and PPARgamma agonists are reported to exert anti-proliferative and pro-apoptotic effects in cancer cells. One compound that also increases LPL expression levels but does not possess PPAR agnostic activity is NO-1886. When given at 400 or 800 ppm in the diet, it suppresses both hyperlipidemia and intestinal polyp formation in Apc-deficient mice, with elevation of LPL mRNA. In conclusion, a decrease in serum lipid levels by increasing LPL activity may contribute to a reduction in intestinal polyp formation with Apc deficiency. PPARalpha and PPARgamma agonists, as well as NO-1886, could be useful as chemopreventive agents for colon cancer.

Attenuated corticosterone response to chronic ACTH stimulation in hepatic lipase-deficient mice: evidence for a role for hepatic lipase in adrenal physiology

Hepatic lipase (HL), a liver-expressed lipolytic enzyme, hydrolyzes triglycerides and phospholipids in lipoproteins and promotes cholesterol delivery through receptor-mediated whole particle and selective cholesterol uptake. HL activity also occurs in the adrenal glands, which utilize lipoprotein cholesterol to synthesize glucocorticoids in response to pituitary ACTH. It is likely that the role of adrenal HL is to facilitate delivery of exogenous cholesterol for glucocorticoid synthesis. On this basis, we hypothesized that HL deficiency would blunt the glucocorticoid response to ACTH. Furthermore, because exogenous cholesterol also is derived from the LDL receptor (LDLR) pathway, we hypothesized that LDLR deficiency would blunt the response to ACTH. To test these hypotheses, we compared the corticosterone response to eight daily ACTH injections in HL-deficient (hl-/-), LDLR-deficient (Ldlr-/-), and HL- and LDLR-doubly deficient (Ldlr-/- hl-/-) mice with that in wild-type (WT) mice. Plasma corticosterone levels were measured on days 2, 5, and 8. Differences in plasma corticosterone levels between genotypes were analyzed by Kruskal-Wallis one-way ANOVA on ranks and pairwise multiple comparisons by Dunn's test. Our results demonstrate a trend toward reductions in plasma corticosterone levels on day 2 and significant reductions on day 5 and day 8 in the knockout models. Thus, on day 5, plasma corticosterone levels were reduced by 57, 70, and 73% (all P < 0.05) and on day 8 by 76, 59, and 63% (all P < 0.05) in hl-/-, Ldlr-/-, and Ldlr-/- hl-/- mice, respectively. These results demonstrate that HL deficiency, like LDLR deficiency, blunts the adrenal response to chronic ACTH stimulation and suggest a novel role for HL in adrenal physiology.

Transient induction of a variant hepatic lipase messenger RNA by corticotropic hormone in rat adrenals

Hepatic lipase (HL) is present not only in liver, but also in steroidogenic organs, where it is thought to mediate cellular uptake of plasma cholesterol. In rat adrenals and ovaries, the HL gene is transcribed into a variant messenger RNA (mRNA) that lacks exons 1 and 2. Treatment of male Wistar rats with corticotropin resulted in a transient 9-fold increase in the variant HL mRNA in the adrenals, which was paralleled by synthesis of 47- to 49-kilodalton HL-related proteins. In contrast, a delayed, but sustained, 6-fold increase in adrenal HL activity was observed. This difference in time course suggests that the HL activity does not reflect HL-like proteins expressed from the variant mRNA. By Northern blotting, the variant HL mRNA was 2.6 kilobase. By screening a rat genomic library, the 5' end of the variant HL mRNA was located in intron 2 immediately upstream of exon 3. Primer extension analysis mapped the 5' end at nucleotide 465 upstream of exon 3. In promoter-reporter assays, the intron 2 region (-233/+350 with respect to the putative start site) showed no apparent basal activity in HepG2 hepatoma and NCI-H295R adrenocortical cells. The putative promoter in intron 2 was up-regulated in NCI-H295R human adrenocortical cells by treatment with 8-bromo-cyclic adenosine monophosphate. We conclude that intron 2 of the rat HL gene has an alternative promoter with low activity in adrenals, ovaries, and liver. In rat adrenals, this promoter is transiently activated by corticotropin.

Serum lipoprotein lipase concentration and risk for future coronary artery disease: the EPIC-Norfolk prospective population study

BACKGROUND

Lipoprotein lipase (LPL) is associated with coronary artery disease (CAD) risk, but prospective population data are lacking. This is mainly because of the need for cumbersome heparin injections, which are necessary for LPL measurements. Recent retrospective studies, however, indicate that LPL concentration can be reliably measured in serum that enabled evaluation of the prospective association between LPL and future CAD.

METHODS AND RESULTS

LPL concentration was determined in serum samples of men and women in the EPIC-Norfolk population cohort who developed fatal or nonfatal CAD during 7 years of follow-up. For each case (n=1006), 2 controls, matched for age, sex, and enrollment time, were identified. Serum LPL concentration was lower in cases compared with controls (median and interquartile range: 61 [43-85] versus 66 [46-92] ng/mL; P<0.0001). Those in the highest LPL concentration quartile had a 34% lower risk for future CAD compared with those in the lowest quartile (odds ratio [OR] 0.66; confidence interval [CI], 0.53 to 0.83; P<0.0001). This effect remained significant after adjustment for blood pressure, diabetes, smoking, body mass index, and low-density lipoprotein (LDL) cholesterol (OR, 0.77; CI, 0.60-0.99; P=0.02). As expected from LPL biology, additional adjustments for either high-density lipoprotein cholesterol (HDL-C) or triglyceride (TG) levels rendered loss of statistical significance. Of interest, serum LPL concentration was positively linear correlated with HDL and LDL size.

CONCLUSIONS

Reduced levels of serum LPL are associated with an increased risk for future CAD. The data suggest that high LPL concentrations may be atheroprotective through decreasing TG levels and increasing HDL-C levels.

Molecular characterization of gilthead sea bream (Sparus aurata) lipoprotein lipase. Transcriptional regulation by season and nutritional condition in skeletal muscle and fat storage tissues

Lipoprotein lipase (LPL) of gilthead sea bream (Sparus aurata) was cloned and sequenced using a RT-PCR approach completed by 3' and 5'RACE assays. The nucleotide sequence covered 1669 bp with an open reading frame of 525 amino acids, including a putative signal peptide of 23 amino acids long. Sequence alignment and phylogenetic analysis revealed a high degree of conservation among most fish and higher vertebrates, retaining the consensus sequence the polypeptide "lid", the catalytic triad and eight cysteine residues at the N-terminal region. A tissue-specific regulation of LPL was also found on the basis of changes in season and nutritional condition as a result of different dietary protein sources. First, the expression of LPL in mesenteric adipose tissue was several times higher than in liver and skeletal muscle. Secondly, the spring up-regulation of LPL expression in the mesenteric adipose tissue was coincident with a pronounced increase of whole body fat content. Thirdly, the highest expression of LPL in the skeletal muscle was found in summer, which may serve to cover the increased energy demands for muscle growth and protein accretion. Further, in fish fed plant-protein-based diets, hepatic LPL expression was up-regulated whereas an opposite trend was found in the mesenteric adipose tissue, which may contribute to drive dietary lipids towards liver fat storage. Finally, it is of interest that changes in circulating triglyceride (TG) levels support the key role of LPL in the clearance of TG-rich lipoproteins. This study is the first report in fish of a co-regulated expression of LPL in oxidative and fat storage tissues under different physiological conditions.

Concurrent suppression of hyperlipidemia and intestinal polyp formation by NO-1886, increasing lipoprotein lipase activity in Min mice

We have previously reported a hyperlipidemic state in two strains of Apc-deficient mice, Min and Apc(1309), associated with low expression levels of lipoprotein lipase (LPL) in the liver and small intestine, and enforced induction of LPL mRNA by peroxisome proliferator-activated receptor (PPAR)alpha and PPARgamma agonists clearly suppressed hyperlipidemia and intestinal polyp formation in these mice. Meanwhile, a compound, NO-1886, has been shown to increase LPL mRNA and protein levels but not to possess PPARalpha and PPARgamma agonistic activity. In this study, therefore, the effects of NO-1886 on hyperlipidemia and intestinal polyp formation were investigated in Min mice. Administration of 400 and 800 ppm NO-1886 in the diet for 13 weeks from 7 weeks of age caused a reduction of serum triglycerides to 39% and 31% of the untreated value, respectively, and the values for very low-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol were improved almost to the wild-type level with a corresponding elevation of the LPL mRNA. Moreover, total numbers of intestinal polyps in the groups receiving NO-1886 at 400 and 800 ppm were decreased to 48% and 42% of the control value, respectively. We also found that NO-1886 suppressed cyclooxygenase-2 transcriptional promoter activity in a reporter gene assay and reduced cyclooxygenase-2 mRNA levels in the small intestine of Min mice. These results indicate that suppression of serum lipid levels by increasing LPL activity may contribute to a reduction of intestinal polyp formation with Apc-deficiency, and NO-1886 and its derivatives could be useful as chemopreventive agents for colon cancer.

Peroxisome Proliferator-Activated Receptor Agonists Modulate Heart Function in Transgenic Mice with Lipotoxic Cardiomyopathy

hLpL(GPI) transgenic mice that overexpress human lipoprotein lipase (hLpL) with a glycosylphosphatidylinositol anchor on cardiomyocytes develop lipotoxic cardiomyopathy associated with increased cardiac uptake of plasma lipids. We hypothesized that peroxisome proliferator-activated receptor (PPAR)alpha, PPARgamma, or a PPARalpha/gamma agonist would alter cardiac function by modulating lipid uptake by the heart. hLpL(GPI) mice were administered rosiglitazone (10 mg/kg/day), fenofibrate (100 mg/kg/day), or DRF2655, an alkoxy propanoic acid analog (10 mg/kg/day), for 16 days. Rosiglitazone reduced plasma triglyceride (TG) from 107.63 +/- 6.98 to 77.61 +/- 3.98 mg/dl, whereas fenofibrate had no effect. DRF2655 reduced TG to 33.17 +/- 4.12 mg/dl. Rosiglitazone and DRF2655 decreased heart TG and total cholesterol; fenofibrate had no effect. Molecular markers for cardiac dysfunction, atrial natriuretic factor, brain natriuretic peptide, and tumor necrosis factor-alpha were decreased with rosiglitazone and increased with fenofibrate. Echocardiographic measurements showed reduced fractional shortening and increased left ventricular systolic dimension with fenofibrate. No changes in these parameters were observed with rosiglitazone or DRF2655 treatment. Muscle-specific carnitine palmitoyltransferase-1 and fatty acid transporter protein-1 gene expression were increased with fenofibrate and DRF2655 treatment; no change in expression of these genes was noted with rosiglitazone treatment. Rosiglitazone and DRF2655 reduced TG uptake by the heart, and fenofibrate treatment increased fatty acid uptake. Thus, in a lipotoxic cardiomyopathy mouse model, a PPARgamma agonist reduced cardiac lipid and markers of cardiomyopathy, whereas an agonist of PPARalpha did not improve cardiac lipids and worsened heart function. These changes were paralleled by alterations in heart lipid uptake. Overall, PPAR activators exhibit differential effects in this model of lipotoxic dilated cardiomyopathy.

Expression of the endothelial lipase gene in murine embryos and reproductive organs

Endothelial lipase (EL) is a recently discovered member of the triglyceride-lipase family that is involved in plasma HDL metabolism. In this study, we investigated the putative role of EL in mouse reproduction by studying EL gene expression in mouse embryos and adult reproductive organs. PCR analysis revealed that EL mRNA is expressed in mouse embryos on embryonic day 8.5 (E8.5) to E11.5, but not later in development. In situ hybridization studies on E10.5 whole embryos and embryonic sections showed expression of EL mRNA in multiple tissues, although of varying intensity. High expression was found in the neuroepithelium of the brain and the neural tube, the mesenchymal cells between organs, the optic lens and cup, and the otocyst. In adult mice, EL mRNA expression was high in ovaries from pregnant mice but low in ovaries from nonpregnant mice. EL mRNA was also highly expressed in placenta and testes. In situ hybridization studies demonstrated intense EL mRNA staining of lutein cells in corpora lutei in ovaries, of spermatocytes in the late pachytene and diplotene stages in testes, and of principal cells in epididymis. These results suggest that EL, in addition to its effects on plasma lipoprotein metabolism, plays a role in murine reproduction.