Common mutations of the lipoprotein lipase gene and their clinical significance

Understanding Hypertriglyceridemia: Integrating Genetic Insights

Hypertriglyceridemia is an exceptionally complex metabolic disorder characterized by elevated plasma triglycerides associated with an increased risk of acute pancreatitis and cardiovascular diseases such as coronary artery disease. Its phenotype expression is widely heterogeneous and heavily influenced by conditions as obesity, alcohol consumption, or metabolic syndromes. Looking into the genetic underpinnings of hypertriglyceridemia, this review focuses on the genetic variants in LPL, APOA5, APOC2, GPIHBP1 and LMF1 triglyceride-regulating genes reportedly associated with abnormal genetic transcription and the translation of proteins participating in triglyceride-rich lipoprotein metabolism. Hypertriglyceridemia resulting from such genetic abnormalities can be categorized as monogenic or polygenic. Monogenic hypertriglyceridemia, also known as familial chylomicronemia syndrome, is caused by homozygous or compound heterozygous pathogenic variants in the five canonical genes. Polygenic hypertriglyceridemia, also known as multifactorial chylomicronemia syndrome in extreme cases of hypertriglyceridemia, is caused by heterozygous pathogenic genetic variants with variable penetrance affecting the canonical genes, and a set of common non-pathogenic genetic variants (polymorphisms, using the former nomenclature) with well-established association with elevated triglyceride levels. We further address recent progress in triglyceride-lowering treatments. Understanding the genetic basis of hypertriglyceridemia opens new translational opportunities in the scope of genetic screening and the development of novel therapies.

Current Data and New Insights into the Genetic Factors of Atherogenic Dyslipidemia Associated with Metabolic Syndrome

Atherogenic dyslipidemia plays a critical role in the development of metabolic syndrome (MetS), being one of its major components, along with central obesity, insulin resistance, and hypertension. In recent years, the development of molecular genetics techniques and extended analysis at the genome or exome level has led to important progress in the identification of genetic factors (heritability) involved in lipid metabolism disorders associated with MetS. In this review, we have proposed to present the current knowledge related to the genetic etiology of atherogenic dyslipidemia, but also possible challenges for future studies. Data from the literature provided by candidate gene-based association studies or extended studies, such as genome-wide association studies (GWAS) and whole exome sequencing (WES,) have revealed that atherogenic dyslipidemia presents a marked genetic heterogeneity (monogenic or complex, multifactorial). Despite sustained efforts, many of the genetic factors still remain unidentified (missing heritability). In the future, the identification of new genes and the molecular mechanisms by which they intervene in lipid disorders will allow the development of innovative therapies that act on specific targets. In addition, the use of polygenic risk scores (PRS) or specific biomarkers to identify individuals at increased risk of atherogenic dyslipidemia and/or other components of MetS will allow effective preventive measures and personalized therapy.

Etiologic Puzzle of Coronary Artery Disease: How Important Is Genetic Component?

In the modern era, coronary artery disease (CAD) has become the most common form of heart disease and, due to the severity of its clinical manifestations and its acute complications, is a major cause of morbidity and mortality worldwide. The phenotypic variability of CAD is correlated with the complex etiology, multifactorial (caused by the interaction of genetic and environmental factors) but also monogenic. The purpose of this review is to present the genetic factors involved in the etiology of CAD and their relationship to the pathogenic mechanisms of the disease. Method: we analyzed data from the literature, starting with candidate gene-based association studies, then continuing with extensive association studies such as Genome-Wide Association Studies (GWAS) and Whole Exome Sequencing (WES). The results of these studies revealed that the number of genetic factors involved in CAD etiology is impressive. The identification of new genetic factors through GWASs offers new perspectives on understanding the complex pathophysiological mechanisms that determine CAD. In conclusion, deciphering the genetic architecture of CAD by extended genomic analysis (GWAS/WES) will establish new therapeutic targets and lead to the development of new treatments. The identification of individuals at high risk for CAD using polygenic risk scores (PRS) will allow early prophylactic measures and personalized therapy to improve their prognosis.

Genome-wide expression reveals potential biomarkers in breast cancer bone metastasis

Breast cancer metastases are most commonly found in bone, an indication of poor prognosis. Pathway-based biomarkers identification may help elucidate the cellular signature of breast cancer metastasis in bone, further characterizing the etiology and promoting new therapeutic approaches. We extracted gene expression profiles from mouse macrophages from the GEO dataset, GSE152795 using the GEO2R webtool. The differentially expressed genes (DEGs) were filtered by log2 fold-change with threshold 1.5 (FDR < 0.05). STRING database and Enrichr were used for GO-term analysis, miRNA and TF analysis associated with DEGs. Autodock Vienna was exploited to investigate interaction of anti-cancer drugs, Actinomycin-D and Adriamycin. Sensitivity and specificity of DEGs was assessed using receiver operating characteristic (ROC) analyses. A total of 61 DEGs, included 27 down-regulated and 34 up-regulated, were found to be significant in breast cancer bone metastasis. Major DEGs were associated with lipid metabolism and immunological response of tumor tissue. Crucial DEGs, Bcl3, ADGRG7, FABP4, VCAN, and IRF4 were regulated by miRNAs, miR-497, miR-574, miR-138 and TFs, CCDN1, STAT6, IRF8. Docking analysis showed that these genes possessed strong binding with the drugs. ROC analysis demonstrated Bcl3 is specific to metastasis. DEGs Bcl3, ADGRG7, FABP4, IRF4, their regulating miRNAs and TFs have strong impact on proliferation and metastasis of breast cancer in bone tissues. In conclusion, present study revealed that DEGs are directly involved in of breast tumor metastasis in bone tissues. Identified genes, miRNAs, and TFs can be possible drug targets that may be used for the therapeutics. However, further experimental validation is necessary.

Case Report: Genetic Analysis of PEG-Asparaginase Induced Severe Hypertriglyceridemia in an Adult With Acute Lymphoblastic Leukaemia

PEG-Asparaginase (also known as Pegaspargase), along with glucocorticoids (predominantly prednisolone or dexamethasone) and other chemotherapeutic agents (such as cyclophosphamide, idarubicin, vincristine, cytarabine, methotrexate and 6-mercaptopurine) is the current standard treatment for acute lymphoblastic leukaemia in both children and adults. High doses of PEG-asparaginase are associated with side effects such as hepatotoxicity, pancreatitis, venous thrombosis, hypersensitivity reactions against the drug and severe hypertriglyceridemia. We report a case of a 28-year-old male who was normolipidemic at baseline and developed severe hypertriglyceridemia (triglycerides of 1793 mg/dl) following treatment with PEG-asparaginase for acute lymphoblastic leukaemia. Thorough genetic analysis was conducted to assess whether genetic variants could suggest a predisposition to this drug-induced metabolic condition. This genetic analysis showed the presence of a rare heterozygous missense variant c.11G > A-p.(Arg4Gln) in the APOC3 gene, classified as a variant of uncertain significance, as well as its association with four common single nucleotide polymorphisms (SNPs; c.*40C > G in APOC3 and c.*158T > C; c.162-43G > A; c.-3A > G in APOA5) related to increased plasma triglyceride levels. To our knowledge this is the first case that a rare genetic variant associated to SNPs has been related to the onset of severe drug-induced hypertriglyceridemia.

Genetic association of LPL rs326 with BMI among the Kuwaiti population

Supplemental Digital Content is available in the text.

Lipoprotein lipase is a key enzyme in lipid metabolism with reported variants associated with obesity, hypertension, type 2 diabetes, and coronary heart disease. This study was performed to investigate the association between common lipoprotein lipase single nucleotide polymorphisms and metabolic disorders in a sample of Kuwaiti cohort (n = 494). Five lipoprotein lipase variants (rs1801177, rs295, rs326, ss2137497749, and ss2137497750) across the lipoprotein lipase gene were genotyped by real-time PCR employing the TaqMan allele discrimination assay. Genotype, allelic frequencies, and Hardy-Weinberg Equilibrium were determined for each variant in the cohort followed by multivariate and logistic regression analysis. A novel finding was observed for the G allele of single nucleotide polymorphism rs326 which was associated with increased BMI after adjusting for age and sex (β = 1.04; 95% confidence interval = 0.15–1.94; P = 0.02). Moreover, a significant difference in the distribution of the minor C allele of rs295 among coronary heart disease subjects compared with noncoronary heart disease, however, this significance was diminished after controlling for age, sex, and BMI. This study demonstrated that lipoprotein lipase rs326 may be indicative for the increased risk of obesity and possibly rs295 for coronary heart disease. The findings are also in agreement with other reports suggesting that intronic variants are important genetic markers in association studies. The findings warrant further studies in a large cohort to confirm and validate the results presented.

Gualou Xiebai Banxia decoction ameliorates Poloxamer 407-induced hyperlipidemia

ETHNOPHARMACOLOGICAL RELEVANCE

Gualou Xiebai Banxia (GLXBBX) decoction is a well-known traditional Chinese herbal formula that was first discussed in the Synopsis of the Golden Chamber by Zhang Zhongjing in the Eastern Han Dynasty. In traditional Chinese medicine, GLXBBX is commonly prescribed to treat cardiovascular diseases, such as coronary heart disease and atherosclerosis.

OBJECTIVE

The present study aimed to examine GLXBBX's preventative capacity and elucidate the potential molecular mechanism of Poloxamer 407 (P407)-induced hyperlipidemia in rats.

MATERIALS AND METHODS

Both the control and model groups received pure water, and the test group also received a GLXBBX decoction. For each administration, 3 ml of the solution was administered orally. To establish hyperlipidemia, a solution mixed with 0.25 g/kg P407 dissolved in 0.9% normal saline was injected slowly into the abdominal cavity. At the end of the study, the rats' plasma lipid levels were calculated using an automatic biochemical analyzer to evaluate the preventative capability of the GLXBBX decoction, and the serum and liver of the rats were collected.

RESULTS

The GLXBBX decoction significantly improved P407-induced hyperlipidemia, including increased plasma triglycerides (TGs), aspartate aminotransferase (AST) elevation, and lipid accumulation. Moreover, GLXBBX decoction treatment increased lipoprotein lipase (LPL) activity and mRNA expression of LPL. Furthermore, GLXBBX significantly suppressed the mRNA expression of stearoyl-CoA desaturase (SCD1).

CONCLUSION

GLXBBX significantly improved P407-induced hyperlipidemia, which may have been related to enhanced LPL activity, increased LPL mRNA expression, and decreased mRNA expression of SCD1.

Association of Metabolic Syndrome with Aerobic Exercise and LPL rs3779788 Polymorphism in Taiwan Biobank Individuals

PURPOSE

The Lipoprotein lipase (LPL) gene is a significant contributor to dyslipidemia. It has shown associations with several conditions including atherosclerosis, obesity, and metabolic syndrome (MetS). We assessed the interactive association between MetS and rs3779788 of the LPL gene based on aerobic exercise.

MATERIALS AND METHODS

Data were available for 7532 Taiwan Biobank (TWB) participants recruited between 2008 and 2016. We used multiple logistic regression to determine the odds ratios (OR) for MetS and their 95% confident intervals (C.I.). Potential variables included LPL rs3779788, aerobic exercise, sex, age, education, marital status, body mass index (BMI), smoking, alcohol consumption, midnight snacking, vegetarian diet, coffee, dietary fat, and tea drinking.

RESULTS

Aerobic exercise was protective against MetS (OR, 0.858; 95% C.I., 0.743-0.991). Compared to CC/CT genotype, the OR for developing MetS was 0.875, (95% C.I., 0.571-1.341) in TT individuals. The test for interaction was significant for the rs3779788 variant and aerobic exercise (p = 0.0484). In our group analyses, the OR for MetS was 0.841 (95% C.I., 0.727-0.974) in CC/CT and 4.076 (95% C.I., 1.158-14.346) in TT individuals who did aerobic exercise compared to those who did not.

CONCLUSION

Our study indicated that aerobic exercise improved metabolic syndrome in Taiwanese adults with rs3779788 CC/CT genotype relative to those with TT genotype.

Advances in Research on the Bioactivity of Alginate Oligosaccharides

Alginate is a natural polysaccharide present in various marine brown seaweeds. Alginate oligosaccharide (AOS) is a degradation product of alginate, which has received increasing attention due to its low molecular weight and promising biological activity. The wide-ranging biological activity of AOS is closely related to the diversity of their structures. AOS with a specific structure and distinct applications can be obtained by different methods of alginate degradation. This review focuses on recent advances in the biological activity of alginate and its derivatives, including their anti-tumor, anti-oxidative, immunoregulatory, anti-inflammatory, neuroprotective, antibacterial, hypolipidemic, antihypertensive, and hypoglycemic properties, as well as the ability to suppress obesity and promote cell proliferation and regulate plant growth. We hope that this review will provide theoretical basis and inspiration for the high-value research developments and utilization of AOS-related products.

Rare LPL gene missense mutation in an infant with hypertriglyceridemia

BACKGROUND

Severe hypertriglyceridemia usually results from a combination of genetic and environmental factors and is most often attributable to mutations in the lipoprotein lipase (LPL) gene.

OBJECTIVES

The aim of this study was to identify rare mutations in the LPL gene causing severe hypertriglyceridemia.

METHODS

A Chinese infant who presented classical features of severe hypertriglyceridemia recruited for DNA sequencing of the LPL gene. The pathogenicity grade of the variants was defined based on the prediction of pathogenicity using in silico prediction tools. Review some studies to understand the molecular mechanisms underlying the severe hypertriglyceridemia.

RESULTS

We identified a rare mutation in the LPL gene causing severe hypertriglyceridemia: a nucleotide substitution (c.836T>G) resulting in a leucine to arginine substitution at position 279 of the protein (p.Leu279Arg).The pathogenicity of the variant was predicted by in silico analysis using PolyPhen2 and SIFT prediction programs, which indicated that mutation p.Leu279Arg is probably harmful. We have also reviewed published studies concerning the molecular mechanisms underlying severe hypertriglyceridemia. A missense mutation in the 6 exon of the LPL gene is reportedly associated with LPL deficiency.

CONCLUSIONS

We have here identified a rare pathogenic mutation in the LPL gene in a Chinese infant with severe hypertriglyceridemia.

Adipose Tissue LPL Methylation is Associated with Triglyceride Concentrations in the Metabolic Syndrome

BACKGROUND

DNA methylation is one of the epigenetic mechanisms that regulate gene expression. DNA methylation may be modified by environmental and nutritional factors. Thus, epigenetics could potentially provide a mechanism to explain the etiology of metabolic disorders, such as metabolic syndrome (MetS). The aim of this study was to analyze the level of DNA methylation of several lipoprotein lipase (LPL)-promoter-CpG dinucleotides in a CpG island region and relate this to the gene and protein expression levels in human visceral adipose tissue (VAT) from individuals with and without MetS.

METHODS

VAT samples were collected from laparoscopic surgical patients without and with MetS, and levels of LPL mRNA, LPL protein, and LPL DNA methylation were measured by qPCR, western blot, and pyrosequencing. Biochemical and anthropometric variables were analyzed. Individuals included in a subset underwent a dietary fat challenge test, and levels of postprandial triglycerides were determined.

RESULTS

We found higher levels of DNA methylation in MetS patients but lower gene expression and protein levels. There was a negative association between LPL methylation and LPL gene expression. We found a positive association between LPL methylation status and abnormalities of the metabolic profile and basal and postprandial triglycerides, whereas LPL gene expression was negatively associated with these abnormalities.

CONCLUSIONS

We demonstrate that LPL methylation may be influenced by the degree of metabolic disturbances and could be involved in triglyceride metabolism, promoting hypertriglyceridemia and subsequent associated disorders, such as MetS.

Computational analysis and enzyme assay of inhibitor response to disease single nucleotide polymorphisms (SNPs) in lipoprotein lipase

Lipoprotein lipase (LPL) is the rate-limiting enzyme for the hydrolysis of the triglyceride (TG) core of circulating TG-rich lipoproteins, chylomicrons, and very low-density lipoproteins. The enzyme has been established as an efficacious and safe therapeutic target for the management of obesity. Here, a systematic profile of the lipase inhibitor response of three anti-obesity agents (Orlistat, Lipstatin, and Cetilistat) to clinical LPL missense mutations arising from disease single nucleotide polymorphisms (SNPs) was established by integrating complex structure modeling, virtual mutagenesis, molecular dynamics (MD) simulations, binding energy analysis, and radiolabeled TG hydrolysis assays. The profile was then used to characterize the resistance and sensitivity of systematic mutation–inhibitor pairs. It is suggested that the Orlistat and Lipstatin have a similar response profile to the investigated mutations due to their homologous chemical structures, but exhibit a distinct profile to that of Cetilistat. Most mutations were predicted to have a modest or moderate effect on inhibitor binding; they are located far away from the enzyme active site and thus can only influence the binding limitedly. A number of mutations were found to sensitize or cause resistance for lipase inhibitors by directly interacting with the inhibitor ligands or by indirectly addressing allosteric effect on enzyme active site. Long-term MD simulations revealed a different noncovalent interaction network at the complex interfaces of Orlistat with wild-type LPL as well as its sensitized mutant H163R and resistant mutant I221T.

Insulin resistance caused by lipotoxicity is related to oxidative stress and endoplasmic reticulum stress in LPL gene knockout heterozygous mice

OBJECTIVE

To investigate the correlation of hypertriglyceridemia with abnormal glucose metabolism and insulin resistance.

METHODS

Lipid and glucose metabolism, whole-body and tissue-specific insulin sensitivity, genes and proteins related with oxidative stress and endoplasmic reticulum (ER) stress were compared between LPL+/- and control mice at different weeks of age.

RESULTS

16-50-week LPL+/- mice had increased body weight compared with their respective controls. Fat mass in visceral adipose tissue (VAT) of 16 and 28-week LPL+/- mice were twice more than their control littermates, and 50-week LPL+/- mice showed the same trend of increase. Plasma lipids were higher in 16-50-week LPL+/- mice. 28- and 50-week LPL+/- mice had elevated tissue lipid accumulation (liver, skeletal muscle, pancreas) and impaired glucose tolerance, while 16-week LPL+/- mice showed no differences. Homeostasis model assessment of insulin resistance for 28 and 50-week LPL+/- mice were twofold greater, whereas that for 16-week LPL+/- mice had no change. Insulin-stimulated phosphorylated Akt (Ser473) in VAT of 28-week LPL+/- mice decreased by 80.6% (p = 0.001), and that in liver and skeletal muscle decreased by 62.4% (P < 0.001) and 51.8% (p = 0.005) respectively. Then we found that plasma malondialdehyde and reactive oxygen species levels in liver and skeletal muscle of LPL+/- mice were elevated. Increased ER stress biomarkers were also detected in liver and VAT of 28-week LPL+/- mice.

CONCLUSIONS

Systemic LPL deletion results in impaired glucose tolerance, whole-body and tissue-specific insulin resistance, which is associated with tissue lipid deposition in various insulin target tissues. Furthermore, the activation of oxidative stress and ER stress may play an important role in the development of tissue-specific and systemic insulin resistance.

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.

Increase of oxidant-related triglycerides and phosphatidylcholines in serum and small intestinal mucosa during development of intestinal polyp formation in Min mice

Recent epidemiological studies have shown a positive association of a high-fat diet with the risk of colon cancer. Indeed, increments in the serum levels of triglycerides (TG) and cholesterols are positively related with colon carcinogenesis. We previously reported that an age-dependent hyperlipidemic state is characteristic of Min mice, an animal model for human familial adenomatous polyposis (FAP). However, qualitative and quantitative changes of lipid metabolism are poorly understood in this state. Here, we provide detailed analysis of serum lipids in Min mice using reverse-phased liquid chromatography/electrospray ionization mass spectrometry (RPLC/ESI-MS). We also demonstrate local analysis of lipid droplets in the villi of the small intestine using laser capture microdissection and a sensitive chip-based nanoESI-MS system. As a result, oxidized phosphatidylcholines (PC) such as aldehyde and carboxylic acid types were increased, even at an early stage of intestinal polyp formation in serum. In addition, hydroperoxidizable TG precursors containing linoleic acid (18:2n-6) were deposited at the tip of the villi with aging, and these hydroperoxidized TG were also increased in serum. Meanwhile, increments of the oxidizable TG precursors in serum and small intestinal mucosa were suppressed by treatment with pitavastatin, a novel third generation lipophilic statin. These results suggest that quantitative and qualitative lipid changes such as hydroperoxidizable TG precursors are important in the course of intestinal polyp formation and oxidative stress might lead to the development of intestinal polyp formation in Min mice.

Glucose intolerance and decreased early insulin response in mice with severe hypertriglyceridemia

Hypertriglyceridemia (HTG) is one of the key features of dyslipidemia in type 2 diabetes, caused by the overproduction and/or decreased clearance of triglyceride (TG)-rich lipoproteins, and significantly promotes the development of cardiovascular diseases in diabetes. However, the effect of severe HTG on glucose metabolism has not previously been determined. Lipoprotein lipase (LPL) deficiency results in severe HTG in humans. By using LPL-deficient mice with severe HTG, we assessed the impact of severe HTG on insulin secretion and glucose tolerance in the present study. While young LPL-deficient mice (4 months of age) showed higher fasting blood glucose (7.42 ± 0.84 versus 4.8 ± 0.80 mmol/L, P < 0.01) and lower insulin concentrations (0.16 ± 0.03 versus 0.48 ± 0.14 ng/mL, P < 0.05), old mice (12 months of age) had higher insulin (1.70 ± 0.35 versus 0.77 ± 0.04 ng/mL, P < 0.05) but normal fasting blood glucose concentrations. Both young and old mice had elevated free fatty acid (FFA) concentrations and exhibited decreased early insulin response; however, only old mice showed impaired glucose tolerance, as compared with wild-type mice of a similar age. Morphological assessment showed enlarged islets in old LPL-deficient mice. These findings suggest that different tests for glucose homeostasis may be needed for patients with LPL deficiency and severe HTG, even though their glucose concentrations are normal at initial screening.

Overexpression of low-density lipoprotein receptor and lipid accumulation in intestinal polyps in Min mice

Apc-deficient Min mice feature low expression of lipoprotein lipase (LPL), high concentration of serum triglyceride (TG), fatty change of the liver and large numbers of intestinal polyps. We have reported that induction of LPL expression reduces serum lipid, especially TG, improves fatty change of the liver and inhibits intestinal polyp formation in the mice. In this study, fatty change/lipid accumulation in intestinal mucosa and polyps in Min mice were analyzed by Oil-red O staining and electron microscopy. A number of large lipid droplets were found in the epithelia of the upper part of polyps. On the other hand, small lipid droplets were only slightly observed at the tip of the villi in non-tumoros parts of the small intestine of Min mice and in the villi of wild-type mice. Moreover, low-density lipoprotein receptor (LDLR) was overexpressed in the area where lipid droplets were observed. The expression levels of LDLR mRNA in the intestinal polyps of Min mice were approximately 3 times higher compared to those in the non-tumoros parts. Remarkable expression of cyclooxygenase-2 was mainly distributed in stromal cells and some in epithelial cells. It is speculated that lipid accumulation in the intestinal polyps may play an important role in intestinal polyp formation in Apc-deficient mice.

Lipoprotein lipase: from gene to obesity

Lipoprotein lipase (LPL) is a multifunctional enzyme produced by many tissues, including adipose tissue, cardiac and skeletal muscle, islets, and macrophages. LPL is the rate-limiting enzyme for the hydrolysis of the triglyceride (TG) core of circulating TG-rich lipoproteins, chylomicrons, and very low-density lipoproteins (VLDL). LPL-catalyzed reaction products, fatty acids, and monoacylglycerol are in part taken up by the tissues locally and processed differentially; e.g., they are stored as neutral lipids in adipose tissue, oxidized, or stored in skeletal and cardiac muscle or as cholesteryl ester and TG in macrophages. LPL is regulated at transcriptional, posttranscriptional, and posttranslational levels in a tissue-specific manner. Nutrient states and hormonal levels all have divergent effects on the regulation of LPL, and a variety of proteins that interact with LPL to regulate its tissue-specific activity have also been identified. To examine this divergent regulation further, transgenic and knockout murine models of tissue-specific LPL expression have been developed. Mice with overexpression of LPL in skeletal muscle accumulate TG in muscle, develop insulin resistance, are protected from excessive weight gain, and increase their metabolic rate in the cold. Mice with LPL deletion in skeletal muscle have reduced TG accumulation and increased insulin action on glucose transport in muscle. Ultimately, this leads to increased lipid partitioning to other tissues, insulin resistance, and obesity. Mice with LPL deletion in the heart develop hypertriglyceridemia and cardiac dysfunction. The fact that the heart depends increasingly on glucose implies that free fatty acids are not a sufficient fuel for optimal cardiac function. Overall, LPL is a fascinating enzyme that contributes in a pronounced way to normal lipoprotein metabolism, tissue-specific substrate delivery and utilization, and the many aspects of obesity and other metabolic disorders that relate to energy balance, insulin action, and body weight regulation.

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.

Is apolipoprotein A5 a novel regulator of triglyceride-rich lipoproteins?

Hypertriglyceridemia is an independent risk factor for the development of cardiovascular disease and is often associated with diabetes, inflammation and the metabolic syndrome. Recently, apolipoprotein A5 (APOA5) was identified as a novel member of the APOA1/C3/A4 gene cluster. Data from mice over-expressing or lacking APOA5 provide direct evidence that this apolipoprotein plays a role in triglyceride metabolism. Moreover, plasma triglyceride levels were found to be strongly associated with APOA5 polymorphisms. The human APOA5 gene is regulated by transcription factors known to affect triglyceride metabolism such as PPARa, RORa, LXR and SREBP-1c and this supports its function. Insulin and interleukins regulate APOA5 gene expression and provide novel clues for the role of this apolipoprotein. To date, the triglyceride lowering action of apoA-V is attributed to the activation of lipoprotein lipase and an acceleration of very low density lipoprotein catabolism. Recent findings indicate that APOA5 could also influence cholesterol homeostasis and probably play a role in hypertriglyceridemia associated with diabetes and inflammation. This review aims to give a comprehensive summary of the current literature and supports the view that APOA5 plays a relevant role in lipid metabolism.

Apolipoprotein A5 and triglyceridemia. Focus on the effects of the common variants

High plasma levels of triglycerides are an independent risk factor for the development of cardiovascular disease. Apolipoprotein A5 (APOA5) is a new member of the apolipoprotein APOA1/C3/A4 gene cluster, found by comparative sequencing analysis. The importance of the APOA5 gene for determination of plasma triglyceride levels has been suggested by the creation of transgenic and knock-out mice (transgenic mice displayed significantly reduced triglycerides, whereas knock-out mice had a high level of triglycerides). It has now been clearly established that distinct polymorphisms in the APOA5 gene consistently influence plasma triglycerides in a wide range of human populations, although some differences between ethnic groups and males and females were described. The possible roles of APOA5 variants in determining the risk of myocardial infarction and coronary artery disease development, as well as in the determination of low-density lipoprotein-particle size or plasma concentrations of C-reactive protein and high-density lipoprotein-cholesterol, are also summarized.

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.

The influence of APOAV polymorphisms (T-1131>C and S19>W) on plasma triglyceride levels and risk of myocardial infarction

The importance of an APOAV gene for plasma triglyceride level determination has been shown on transgenic and knockout mice. We examined whether APOAV variants are associated with plasma triglyceride levels and risk of myocardial infarction (MI). We have evaluated the influence of APOAV polymorphisms (T-1131>C and S19>W) on plasma triglycerides in 1191 males and 1368 females representatively selected from the Czech population. Triglycerides have been analysed in 1997 and 2001. Subsequently, we have analysed the genotype frequencies of the APOAV polymorphism in 435 patients with MI. T-1131>C variation in the APOAV gene affects the plasma triglyceride showing a higher level in C-1131 carriers than in T/T-1131 homozygotes. This association has been observed both in males and females (p < 0.001). Similarly, plasma triglycerides were also significantly influenced by the S19>W APOAV genotypes. In both males and females, the W19 carriers have triglycerides significantly (p < 0.001) higher compared to the S19 homozygotes. In a group of MI patients, the frequency of the rare homozygotes for at least one APOAV polymorphism (C/C-1131 and/or W/W19) was significantly higher than that in the population sample (7.4 vs 2.0%, p < 0.00001). We conclude that variations in the APOAV gene not only play a role in genetic determination of triglyceride levels but also could influence risk of MI.

Lipoprotein lipase gene variants and progression of nephropathy in hypercholesterolaemic patients with type 2 diabetes

OBJECTIVE

Recent prospective studies have identified hyperlipidaemia as an independent determinant of diabetic nephropathy. Lipoprotein lipase (LPL) is a key enzyme in the postprandial processing of triglycerides and VLDL. Among a number of common sequence variants of the LPL, HindIII has been associated with coronary heart disease and, more recently, with microalbuminuria in type 2 diabetes. We evaluated the progression of renal disease in hypercholesterolaemic type 2 diabetic patients in relation to this polymorphism.

DESIGN AND SUBJECTS

We followed up for 4 years 65 consecutively enrolled microalbuminuric patients with type 2 diabetes; of whom 28 had hypercholesterolaemia (6.62 +/- 0.9 mmol L(-1), group A) and 37 were normocholesterolaemic (4.68 +/- 0.5 mmol L(-1), group B).

MAIN OUTCOME MEASURES

After performing the genetic analyses, albumin excretion rate (AER) and estimated glomerular filtration rate (GFR), calculated by the simplified equation of the MDRD Study Group, were repeated every year.

RESULTS

In group A, AER increased more (deltaAER: 11 [38] vs. 4 [18] microg min(-1) per year in group B, P < 0.0001) while GFR declined faster (-3.5 +/- 2.1 vs. -2.0 +/- 1.4 mL min(-1) per year, P < 0.02). Patients homozygous for the allele + of HindIII showed a significantly faster decline of GFR and a higher increase of AER (both P = 0.0001) even after adjustment for cholesterol levels and anthropometric variables.

CONCLUSIONS

In hypercholesterolaemic type 2 diabetic patients with microalbuminuria, the renal disease has an accelerated course, particularly in those carrying the H+/H+ genotype of the HindIII polymorphism at the LPL locus.

Lipoprotein lipase (LPL) gene variation and progression of carotid artery plaque

BACKGROUND AND PURPOSE

Coding single nucleotide polymorphisms (cSNPs) in the lipoprotein lipase (LPL) gene have been associated with lipoprotein phenotypes and vascular disease risk. We studied the association between LPL cSNPs and a novel noninvasive measure of disease, namely, cross-sectional carotid plaque area (CPA) on B-mode ultrasound.

METHODS

Four hundred fifty-two patients from an atherosclerosis prevention clinic had determinations of baseline and total CPA. Traditional atherosclerosis risk factors were recorded, and the LPL D9N, N291S, and S447X cSNPs were genotyped. Multiple regression analysis was used to identify determinants of CPA.

RESULTS

Minor allele frequencies for LPL D9N, N291S, and S447X were 2.8%, 0.9%, and 4.4%, respectively. There were no significant between-genotype differences in treated fasting lipids. The LPL D9N genotype was a significant predictor of both baseline CPA (P=0.008) and plaque progression from baseline to 1 year later (P=0.001). Heterozygotes for the N9 allele had higher mean baseline CPA and plaque progression than did LPL D9/D9 homozygotes.

CONCLUSIONS

LPL D9N genotype may be a determinant of atherosclerosis as estimated by static baseline CPA and by progression of CPA.

Lipoprotein lipase: the regulation of tissue specific expression and its role in lipid and energy metabolism

PURPOSE OF REVIEW

The aim of this review is to summarize and discuss recent advances in the understanding of the physiological role of lipoprotein lipase in lipid and energy metabolism.

RECENT FINDINGS

Studies on the transcriptional and the posttranscriptional level of lipoprotein lipase expression have provided new insights into the complex mechanisms that are involved in the regulation of the enzyme. Additionally a large body of evidence from both human studies and animal models suggests that the level of lipoprotein lipase expression in a given tissue is the rate limiting process for the uptake of triglyceride derived fatty acids. Imbalances in the partitioning of fatty acids among peripheral tissues have major metabolic consequences. For example, in mice both decreased lipoprotein lipase activities in adipose tissue and increased activity in muscle are associated with resistance to obesity; lack of lipoprotein lipase activity in macrophages is correlated with a decreased susceptibility to develop atherosclerotic lesions and overexpression of the enzyme in muscle is associated with increased blood glucose levels and insulin resistance.

SUMMARY

Considering the central role of lipoprotein lipase in energy metabolism it is a reasonable goal to discover and develop new drugs that affect the tissue specific expression pattern of the enzyme.