Lipoprotein Lipase Protein Research Articles

Type 1 Hyperlipoproteinemia and Recurrent Acute Pancreatitis due to Lipoprotein Lipase Antibody in a Young Girl with Sjögren's Syndrome

Type 1 hyperlipoproteinemia (T1HLP) in childhood is most often due to genetic deficiency of lipoprotein lipase (LPL) or other related proteins. The aim was to report a case of marked hypertriglyceridemia and recurrent acute pancreatitis due to the presence of LPL autoantibody in a young girl who was subsequently diagnosed with Sjögren's syndrome. A 9-yr-old African-American girl presented with acute pancreatitis and serum triglycerides of 4784 mg/dl. Strict restriction of dietary fat reduced serum triglycerides, but she continued to experience recurrent pancreatitis. Approximately 18 months thereafter, she developed transient pauciarticular arthritis with elevated serum antinuclear antibody (>1:1280). Minor salivary gland biopsy revealed chronic sialadenitis with a dense periductal lymphocytic aggregate suggestive of Sjögren's syndrome. Genomic DNA was analyzed for LPL, GPIHBP1, APOA5, APOC2, and LMF1. Immunoblotting was performed to detect serum LPL autoantibody. The patient had no disease-causing variants in LPL, GPIHBP1, APOA5, APOC2, or LMF1. Immunoblotting revealed serum LPL antibody. The patient responded to immunosuppressive therapy for Sjögren's syndrome with resolution of hypertriglyceridemia. Unexplained T1HLP in childhood could be secondary to LPL deficiency induced by autoantibodies. Therefore, diagnosis of autoimmune T1HLP should be entertained if clinical features are suggestive of an autoimmune process.

Effects of long-term consumption of low doses of resveratrol on diet-induced mild hypercholesterolemia in pigs: a transcriptomic approach to disease prevention

Metabolic and cardiovascular diseases (CVDs) have risen to alarming proportions, and there is a need for therapeutic and preventive measures. The polyphenol resveratrol (RES) protects against CVDs, but in vivo molecular mechanisms responsible for protection are not yet understood. Peripheral blood mononuclear cells (PBMNCs) are involved in the development of atherosclerosis and metabolic disorders. The identification of PBMNCs genes responding to dietary compounds might help to understand the mechanisms underlying the effects of polyphenols. We determined gene expression differences between PBMNCs from pigs fed a high-fat diet manifesting a mild increase of cholesterol and pigs fed a high-fat diet containing low doses of RES. Although the consumption of RES did not modify the levels of cholesterol, microarray analyses indicated that some of the differentially expressed genes, collagens (COL1A, COL3A), lipoprotein lipase (LPL) and fatty-acid binding proteins (FABPs) involved in CVDs and lipid metabolism were up-regulated by the high-fat diet and down-regulated by RES. Reverse transcriptase polymerase chain reaction confirmed that RES and RES-containing grape extract prevented the induction of FABP4 in PBMNCs in female pigs fed a high-fat diet. Low micromolar concentrations of RES and its metabolite dihydroresveratrol exerted a minor but significant reducing effect on the induction of FABP4 expression in human macrophages treated with oxidized low-density lipoprotein. Our results show that the consumption of low doses of RES modulates the expression of genes related to lipid metabolism and metabolic disorders that are affected by a high-fat diet and suggest that some of the circulating RES metabolites may contribute to these effects.

Effects of increased milking frequency for the first 21 days post partum on selected measures of mammary gland health, milk yield and milk composition

Somatic cell count (SCC) is a widely used marker of udder health and a predictor of inflammation caused by an immune response. The objective of this study was to determine whether selected measures of mammary gland health as well as milk fatty acid profile were altered by an increase in milking frequency using a unilateral frequent milking (UFM) model. Holstein cows at parturition were assigned to UFM, in which the left udder half of each cow was milked four-times daily (4X) and the right udder half was milked twice daily (2X) for the first 21 days in milk (DIM). Milk yields from each udder half were measured from 1-21 DIM and samples were collected on days 3, 7, 10, 14 and 21 for determination of SCC and milk composition. Flow cytometric analysis with bovine monoclonal antibodies was used to identify milk immune cell populations and milk fatty acid (FA) composition was determined using gas chromatography. Gene expression analysis was used to determine whether there was an alteration in mRNA expression of genes involved in milk fat production including lipoprotein lipase (LPL) and FA-binding protein 3 (FABP3) with ribosomal protein S9 (RPS9) as a house-keeping gene. No difference was detected for milk SCC or cell populations between the udder halves milked 4X as compared with the udder halves milked 2X. In addition, no difference was detected for any FA in milk from the udder half milked 4X as compared with the udder half milked 2X. Overall, using a UFM model, increased milking frequency for the first 21 DIM did not affect selected measures of mammary gland health or milk FA, but was associated with greater milk yield, milk fat percent and yield, and milk protein and lactose yields.

Adipose tissue dysfunction and hypertriglyceridemia: mechanisms and management

Elevated plasma triglyceride levels, as often seen in obese subjects, are independently associated with an increased risk of cardiovascular diseases. By secreting adipokines (such as adiponectin and leptin) and other proteins (such as lipoprotein lipase and cholesteryl ester transferase protein), adipose tissue affects triglyceride metabolism. In obesity, adipocyte hypertrophy leads to many changes in adipocyte function and production of anti- and pro-inflammatory cytokines. Furthermore, free fatty acids are released into the circulation contributing to insulin resistance. Adipose tissue dysfunction will eventually lead to abnormalities in lipid metabolism, such as hypertriglyceridemia (due to increased hepatic very-low-density lipoprotein production and decreased triglyceride hydrolysis), small dense low-density lipoprotein particles, remnant lipoproteins and low high-density lipoprotein cholesterol levels, all associated with a higher risk for the development of cardiovascular diseases. The clinical implications of elevated plasma triglycerides are still a matter of debate. Understanding the pathophysiology of adipose tissue dysfunction in obesity, which is becoming a pandemic condition, is essential for designing appropriate therapeutic interventions. Lifestyle changes are important to improve adipose tissue function in obese patients. Pharmacological interventions to improve adipose tissue function need further evaluation. Although statins are not very potent in reducing plasma triglycerides, they remain the mainstay of therapy for cardiovascular risk reduction in high-risk patients.

Sex-Dependent Effects of High-Fat-Diet Feeding on Rat Pancreas Oxidative Stress

The objective of the study was to investigate whether sex differences in oxidative stress-associated insulin resistance previously reported in rats could be attributed to a possible sex dimorphism in pancreas redox status. Fifteen-month-old male and female Wistar rats were fed a control diet or a high-fat diet for 14 weeks. Serum glucose, lipids, and hormone levels were measured. Insulin immunohistochemistry and morphometric analysis of islets were performed. Pancreas triglyceride content, oxidative damage, and antioxidant enzymatic activities were determined. Lipoprotein lipase, hormone-sensitive lipase, and uncoupling protein 2 (UCP2) levels were also measured. Male rats showed a more marked insulin resistance profile than females. In control female rats, pancreas Mn-superoxide dismutase activity and UCP2 levels were higher, and oxidative damage was lower compared with males. High-fat-diet feeding decreased pancreas triglyceride content in female rats and UCP2 levels in male rats. High-fat-diet female rats showed larger islets than both their control and sex counterparts. These results confirm the existence of a sex dimorphism in pancreas oxidative status in both control and high-fat-diet feeding situations, with female rats showing higher protection against oxidative stress, thus maintaining pancreatic function and contributing to a lower risk of insulin resistance.

Abstract 1256: A role for lipoprotein lipase in fatty acid acquisition by breast, prostate and liposarcoma tumors

Abstract The importance of de novo fatty acid (FA) synthesis for tumor cell growth is well established, and we have now examined the hypothesis that the uptake of exogenous FA provides an alternative FA fuel source for tumors. Background: Many tumor cells utilize FA as a major energy source, and they do not survive if the supply is interrupted. In order to obtain lipids, tumors can synthesize fatty acids from glucose-derived precursors using fatty acid synthase (FASN), or they could potentially hydrolyze diet-derived triglycerides from circulating lipoproteins using the enzyme lipoprotein lipase (LPL), and take up the free fatty acids using the cell surface channel CD36. It is also conceivable that they could obtain lipids by receptor-mediated endocytosis, using syndecan (Sdc1) and LPL. The latter two of these three mechanisms have not been examined. Methods: We employed cDNA microarray and quantitative RT-PCR to study mRNA expression, measured secreted LPL enzyme activity, and produced a monoclonal antibody for LPL protein analysis and immunohistochemistry (IHC). We also assessed cellular uptake of fluorescently labeled very low density lipoproteins (VLDL). We studied cell lines and/or tumor tissues for expression of FASN, Spot 14 (a nuclear protein that drives FASN expression), LPL, CD36, and Sdc1. Results: 1. By RT-PCR, FASN and Spot14, a driver of FASN gene expression, are expressed in all cell lines (45 breast cancer, 1 liposarcoma, 1 cervical carcinoma, 3 prostate cancer) and tumor tissues (160 breast cancer, 24 liposarcoma, 10 prostate cancer) examined. 2. By RT-PCR and enzyme activity assays, LPL is expressed only in liposarcoma and triple-negative breast cancer cell lines. Prostate cancer cells secrete negligible LPL. 3. Addition of exogenous LPL and triglyceride substrate to culture media enhanced the growth of breast cancer and liposarcoma cell lines, but not prostate cancer cell lines. 4. Provision of exogenous LPL, however, rescued prostate cancer cell lines from the cytotoxicity of FASN inhibition. 5. siRNA-mediated knockdown of LPL impaired the growth of HeLa cells, 6. In contradistinction to observations in cell lines, IHC demonstrated brisk expression of LPL in all liposarcomas, prostate tumors, and breast cancer tumors examined, irrespective of ER/PR or HER2/neu status. 7. CD36 is expressed in the majority of tumors examined by IHC, including 98% of breast cancers. 8. Sdc1 and CD36 are expressed in triple-negative DU4475 breast cancer cells, but they did not endocytose labeled VLDL particles. Conclusions: These data demonstrate that, in addition to de novo FA synthesis, tumors can utilize diet-derived fat, and that this can fuel their growth. Our findings provide a mechanism, namely lipolysis by LPL and uptake by CD36, for the link between dietary fat intake and tumor progression. Inhibition of lipolysis, as well as lipogenesis, may be a necessary strategy to target the FA requirement of aggressive tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1256. doi:10.1158/1538-7445.AM2011-1256

Lipoprotein Lipase Is a Novel Amyloid β (Aβ)-binding Protein That Promotes Glycosaminoglycan-dependent Cellular Uptake of Aβ in Astrocytes

Lipoprotein lipase (LPL) is a member of a lipase family known to hydrolyze triglyceride molecules in plasma lipoprotein particles. LPL also plays a role in the binding of lipoprotein particles to cell-surface molecules, including sulfated glycosaminoglycans (GAGs). LPL is predominantly expressed in adipose and muscle but is also highly expressed in the brain where its specific roles are unknown. It has been shown that LPL is colocalized with senile plaques in Alzheimer disease (AD) brains, and its mutations are associated with the severity of AD pathophysiological features. In this study, we identified a novel function of LPL; that is, LPL binds to amyloid β protein (Aβ) and promotes cell-surface association and uptake of Aβ in mouse primary astrocytes. The internalized Aβ was degraded within 12 h, mainly in a lysosomal pathway. We also found that sulfated GAGs were involved in the LPL-mediated cellular uptake of Aβ. Apolipoprotein E was dispensable in the LPL-mediated uptake of Aβ. Our findings indicate that LPL is a novel Aβ-binding protein promoting cellular uptake and subsequent degradation of Aβ.

Cooling causes changes in the distribution of lipoprotein lipase and milk fat globule membrane proteins between the skim milk and cream phase

Lipoprotein lipase (LPL) activity and free fatty acid levels were studied in freshly milked, uncooled milk from individual Danish Holstein or Jersey cows, or after storage for up to 24h at either a cooling temperature (4°C) or at the milking temperature (31°C). Upon cooling for up to 24h, LPL activity increased in the cream phase, whereas the activity in the skim milk was steady, as observed for Jersey cows, or increased, as seen for the Holsteins. Storage at 31°C decreased the LPL activity in both the cream phase and the skim milk phase. The increase in free fatty acid levels was found to depend on LPL activity, incubation temperature, substrate availability, and incubation time. Furthermore, the migration of milk proteins between the skim milk phase and the cream phase upon cooling of milk from Jersey cows or from Danish Holstein cows was studied using proteomic methods involving 2-dimensional gel electrophoresis and mass spectrometry. Proteins associated with the milk fat globules were isolated from all milk fractions and analyzed. Major changes in the distributions of proteins between the skim milk phase and the cream phase were observed after cooling at 4°C for 4h, where a total of 29 proteins between the 2 breeds was found to change their association with the milk fat globule membrane (MFGM) significantly. Among these, the MFGM proteins adipophilin, fatty acid-binding protein, and lactadherin, as well as the non-MFGM proteins β-casein, lactoferrin, and heat shock protein-71, were identified. Adipophilin, lactadherin, and lactoferrin were quantitatively more associated with the MFGM upon cold storage at 4°C, whereas β-casein, fatty acid-binding protein, and heat shock protein-71 were found to be less associated with the MFGM upon cold storage.

Unexpected Expression Pattern for Glycosylphosphatidylinositol-anchored HDL-binding Protein 1 (GPIHBP1) in Mouse Tissues Revealed by Positron Emission Tomography Scanning

Glycosylphosphatidylinositol-anchored high density lipoprotein-binding protein 1 (GPIHBP1), a GPI-anchored endothelial cell protein, binds lipoprotein lipase (LPL) and transports it into the lumen of capillaries where it hydrolyzes triglycerides in lipoproteins. GPIHBP1 is assumed to be expressed mainly within the heart, skeletal muscle, and adipose tissue, the sites where most lipolysis occurs, but the tissue pattern of GPIHBP1 expression has never been evaluated systematically. Because GPIHBP1 is found on the luminal face of capillaries, we predicted that it would be possible to define GPIHBP1 expression patterns with radiolabeled GPIHBP1-specific antibodies and positron emission tomography (PET) scanning. In Gpihbp1(-/-) mice, GPIHBP1-specific antibodies were cleared slowly from the blood, and PET imaging showed retention of the antibodies in the blood pools (heart and great vessels). In Gpihbp1(+/+) mice, the antibodies were cleared extremely rapidly from the blood and, to our surprise, were taken up mainly by lung and liver. Immunofluorescence microscopy confirmed the presence of GPIHBP1 in the capillary endothelium of both lung and liver. In most tissues with high levels of Gpihbp1 expression, Lpl expression was also high, but the lung was an exception (very high Gpihbp1 expression and extremely low Lpl expression). Despite low Lpl transcript levels, however, LPL protein was readily detectable in the lung, suggesting that some of that LPL originates elsewhere and then is captured by GPIHBP1 in the lung. In support of this concept, lung LPL levels were significantly lower in Gpihbp1(-/-) mice than in Gpihbp1(+/+) mice. In addition, Lpl(-/-) mice expressing human LPL exclusively in muscle contained high levels of human LPL in the lung.

Duration and Magnitude of Extracellular Signal-Regulated Protein Kinase Phosphorylation Determine Adipogenesis or Osteogenesis in Human Bone Marrow-Derived Stem Cells

PurposeImbalances between osteogenic and adipogenic differentiation leads to diseases such as osteoporosis. The aim of our study was to demonstrate the differences in extracellular signal-regulated kinase (ERK) phosphorylation during both adipogenesis and osteogenesis of human bone marrow-derived stem cells (BMSCs).Materials and MethodsUsing troglitazone, GW9662 and U0126, we investigated their role in hBMSC differentiation to adipogenic and osteogenic fates.ResultsERK1/2 inhibition by U0126 suppressed proliferator-activated receptor (PPAR)γ expression and lipid accumulation, while it decreased the mRNA expression of adipogenic genes (lipoprotein lipase, PPARγ, and adipocyte protein) and osteogenic genes (type I collagen and osteopontin). ERK phosphorylation was transient and decreased during adipogenesis, whereas it occurred steadily during osteogenesis. Troglitazone, a PPARγ agonist, induced adipogenesis by inhibiting ERK phosphorylation even in an osteogenic medium, suggesting that ERK signaling needs to be shut off in order to proceed with adipose cell commitment. Cell proliferation was greatly increased in osteogenesis but was not changed during adipogenesis, indicating that ERK might play different roles in cellular proliferation and differentiation between the two committed cell types.ConclusionThe duration and magnitude of ERK activation might be a crucial factor for the balance between adipogenesis and osteogenesis in human bone marrow-derived stem cells.

Expression of Lipoprotein Lipase In Chronic Lymphocytic Leukemia Cells: Is There a Biological Function?

AbstractAbstract 3580The expression of lipoprotein lipase (LPL) in CLL cells is an established mRNA surrogate marker for immunoglobulin heavy chain (IgVH) mutational status. High expression of LPL correlates with poor prognosis. However, the possible functional role of LPL in CLL is still unclear. LPL is normally expressed in muscle cells, adipose tissue and macrophages, transported to the luminal surface of endothelial cells where it is bound heparan sulfate-proteoglycans (HSPG). Heparin competes with HSPG for the binding sites and intravenous injection leads to elevated plasma LPL protein levels and enzymatic activity (“heparin release test”). LPL mRNA levels correlate with intracellular protein expression (Heintel et al. Leukemia. 2005; Mansouri et al. Leuk Res. 2010). Moreover cellular lysates from CLL patients contain elevated LPL enzymatic activity compared to healthy donors (Pallasch et al. Leukemia. 2008.). In this study, we investigated the basal (pre-heparin) LPL protein levels by enzyme-linked immunosorbent assay in the serum of 42 CLL patients, 14 non-CLL patients (lymphoma in remission), and 4 healthy donors (HD): Median pre-heparin LPL protein levels were 40.10 ng/ml (range: 5.66–108.44), 44.11 ng/ml (18.26-84.08), and 68.14 ng/ml (33.28-174.38), respectively. Among CLL patients there were no significant differences between those with high (N=16; median LPL protein in serum: 38.10 ng/ml (8.72-73.49)) and low (N=26; 43.12 ng/ml (5.66-108.44) (p=0.354) LPL mRNA expression. Thirteen patients with known LPL mRNA expression were investigated for LPL protein “release” after heparin injection. Ten and twenty minutes after 50 U/kg heparin injection, the elevation of both parameters, LPL protein amount in serum and enzymatic activity in plasma, was similar to those of HD normal values. In detail, medium serum protein levels in samples with high LPL mRNA (N=5) increased from 16.11 to 214.33 and 332.78 ng/ml and in the samples with low mRNA (N=8) from 13.08 to 219.68 and 386.65 ng/ml, respectively. The corresponding median values of the LPL enzymatic activities in high vs. low expressors were: 7.25/15.52/20.01 and 7.45/19.13/20.57 μ M/ml/h. In addition, release of LPL from peripheral mononuclear cells (PBMC) of CLL patients (N=3) by heparin in vitro was absent. Cell viability and LPL mRNA expression remained unaffected in both in vivo and in vitro samples after heparin addition. In order to assess the impact of LPL on cell survival, CLL cells were cultured (N=3) for up to 72 hours with different doses of purified LPL protein. There was no positive effect on cell survival irrespective of primary LPL mRNA expression or culture conditions (with or without FCS). Since these results point to an intracellular effect of LPL, we aimed to identify downstream targets by knock down with siRNA against LPL in 7 CLL samples and 5 cell lines (hepatocellular carcinoma, cervix carcinoma, colon carcinoma, multiple myeloma and acute monocytic leukemia) with high LPL mRNA expression. Gene expression changes were analyzed by microarrays (GeneChip® Human Gene 1.0 ST Array, Affymetrix). Fifteen genes were up- (N=4) or downregulated (N=11) in at least 3 of 5 cell lines by more than 1.5-fold (e.g. GSTP1, COROC1). Nine genes were at least 1.5-fold downregulated in parallel with LPL in the CLL samples only. These genes belong to various pathways (e.g. cell cycle, signaling in immune system, metabolism of carbohydrates) and seem to be specific for CLL. Cross-validation of individual genes is under way.Our data suggest that (1) neither basal serum LPL protein levels nor heparin-induced LPL release in CLL patients are suitable clinical prognostic markers; (2) Stimulation with external LPL protein does not affect CLL cell survival; (3) siRNA knock-down of LPL induces changes in various functional pathways. We conclude that the key role of LPL expression in high-risk CLL is related to its (intra)cellular expression. Disclosures:No relevant conflicts of interest to declare.

Apolipoprotein C-II and lipoprotein lipase show a temporal and geographic correlation with surfactant lipid synthesis in preparation for birth

BackgroundFatty acids are precursors in the synthesis of surfactant phospholipids. Recently, we showed expression of apolipoprotein C-II (apoC-II), the essential cofactor of lipoprotein lipase (LPL), in the fetal mouse lung and found the protein on the day of the surge of surfactant synthesis (gestation day 17.5) in secretory granule-like structures in the distal epithelium. In the present study, we will answer the following questions: Does apoC-II protein localization change according to the stage of lung development, thus according to the need in surfactant? Are LPL molecules translocated to the luminal surface of capillaries? Do the sites of apoC-II and LPL gene expression change according to the stage of lung development and to protein localization?ResultsThe present study investigated whether the sites of apoC-II and LPL mRNA and protein accumulation are regulated in the mouse lung between gestation day 15 and postnatal day 10. The major sites of apoC-II and LPL gene expression changed over time and were found mainly in the distal epithelium at the end of gestation but not after birth. Accumulation of apoC-II in secretory granule-like structures was not systematically observed, but was found in the distal epithelium only at the end of gestation and soon after birth, mainly in epithelia with no or small lumina. A noticeable increase in surfactant lipid content was measured before the end of gestation day 18, which correlates temporally with the presence of apoC-II in secretory granules in distal epithelium with no or small lumina but not with large lumina. LPL was detected in capillaries at all the developmental times studied.ConclusionsThis study demonstrates that apoC-II and LPL mRNAs correlate temporally and geographically with surfactant lipid synthesis in preparation for birth and suggests that fatty acid recruitment from the circulation by apoC-II-activated LPL is regionally modulated by apoC-II secretion. We propose a model where apoC-II is retained in secretory granules in distal epithelial cells until the lumina reaches a minimum size, and is then secreted when the rate of surfactant production becomes optimal.

Ochratoxin A Inhibits Adipogenesis Through the Extracellular Signal-Related Kinases–Peroxisome Proliferator-Activated Receptor-γ Pathway in Human Adipose Tissue-Derived Mesenchymal Stem Cells

Ochratoxin A (OTA) is a ubiquitous fungal metabolite with nephrotoxic, carcinogenic, and apoptotic potential. Although the toxic effects of OTA in various cell types are well characterized, it is not known whether OTA has an effect on stem cell differentiation. In this study, we demonstrate that OTA inhibits adipogenesis in human adipose tissue-derived mesenchymal stem cells, as indicated by decreased accumulation of intracellular lipid droplets. Further, OTA significantly reduces expression of adipocyte-specific markers, including peroxisome proliferator-activated receptor-γ (PPAR-γ), CCAAT enhancer binding protein-α (C/EBP-α), lipoprotein lipase (LPL), and adipocyte fatty acid-binding protein (aP2). At the molecular level, OTA phosphorylates PPAR-γ2 through extracellular signal-related kinase activation and inhibits PPAR-γ activity. We also found that treatment with the mitogen-activated protein kinase kinase inhibitor, PD98059, significantly blocked the OTA-induced inhibition of adipogenesis. These results indicate that OTA suppresses adipogenesis in an extracellular signal-related kinase-dependent manner. Taken together, our results suggest a novel effect of OTA on adipocyte differentiation in human adipose tissue-derived mesenchymal stem cells and the possibility that OTA might affect the differentiation of other types of stem cells.

Angiopoietin-like Protein 3 Inhibits Lipoprotein Lipase Activity through Enhancing Its Cleavage by Proprotein Convertases

Lipoprotein lipase (LPL)-mediated lipolysis of triglycerides is the first and rate-limiting step in chylomicron/very low density lipoprotein clearance at the luminal surface of the capillaries. Angiopoietin-like protein 3 (ANGPTL3) is shown to inhibit LPL activity and plays important roles in modulating lipoprotein metabolism in vivo. However, the mechanism by which it inhibits LPL activity remains poorly understood. Using cell-based analysis of the interaction between ANGPTL3, furin, proprotein convertase subtilisin/kexin type 5 (PCSK5), paired amino acid converting enzyme-4 (PACE4), and LPL, we demonstrated that the cleavage of LPL by proprotein convertases is an inactivation process, similar to that seen for endothelial lipase cleavage. At physiological concentrations and in the presence of cells, ANGPTL3 is a potent inhibitor of LPL. This action is due to the fact that ANGPTL3 can enhance LPL cleavage by endogenous furin and PACE4 but not by PCSK5. This effect is specific to LPL but not endothelial lipase. Both N- and C-terminal domains of LPL are required for ANGPTL3-enhanced cleavage, and the N-terminal domain of ANGPTL3 is sufficient to exert its effect on LPL cleavage. Moreover, ANGPTL3 enhances LPL cleavage in the presence of either heparan sulfate proteoglycans or glycosylphosphatidylinositol-anchored high density lipoprotein-binding protein 1 (GPIHBP1). By enhancing LPL cleavage, ANGPTL3 dissociates LPL from the cell surface, inhibiting both the catalytic and noncatalytic functions of LPL. Taken together, our data provide a molecular connection between ANGPTL3, LPL, and proprotein convertases, which may represent a rapid signal communication among different metabolically active tissues to maintain energy homeostasis. These novel findings provide a new paradigm of specific protease-substrate interaction and further improve our knowledge of LPL biology.

Melatonin inhibits adipogenesis and enhances osteogenesis of human mesenchymal stem cells by suppressing PPARγ expression and enhancing Runx2 expression

Adipogenesis and osteogenesis, a reciprocal relationship in bone marrow, are complex processes including proliferation of precursor cells, commitment to the specific lineage, and terminal differentiation. Accumulating evidence from in vitro and in vivo studies suggests that melatonin affects terminal differentiation of osteoblasts and adipocytes, but little is known about the effect of melatonin on the process of adipogenesis and osteogenesis, especially adipogenesis. This study was performed to determine the effect of melatonin on adipogenesis and osteogenesis in human mesenchymal stem cells (hMSCs). Cell proliferation assays demonstrated that melatonin had no apparent effect on the proliferation of hMSCs. When melatonin was added to the adipogenic/osteogenic medium, it directly inhibited adipogenesis and simultaneously promoted osteogenesis of hMSCs in a dose-dependent manner. Furthermore, quantitative RT-PCR demonstrated that melatonin significantly suppressed peroxisome proliferator-activated receptor gamma (PPARγ) expression (day 3, 25% decrease; day 6, 47% decrease), but promoted Runx2 expression (day 3, 87% increase; day 6, 56% increase) in the early stages of adipogenesis and osteogenesis of hMSCs. Moreover, melatonin down-regulated several markers of terminal adipocyte differentiation, including leptin (30%), lipoprotein lipase (LPL, 41%), adiponectin (51%), and adipocyte protein 2 (αP2, 45%). Meanwhile, melatonin up-regulated several markers of osteoblast differentiation, including alkaline phosphatase (110%), osteopontin (218%), and osteocalcin (310%). These results suggest that melatonin directly inhibits hMSCs adipogenic differentiation and significantly enhances hMSCs osteogenic differentiation by suppressing PPARγ expression and enhancing Runx2 expression; this provides further evidence for melatonin as an anti-osteoporosis drug.

Elevated expression of four apolipoprotein genes during the 32–35 week gestation window in the human developing lung

BackgroundCo-expression of four apolipoproteins with a sex difference was observed in the mouse developing lung with an increase during the day of the surge of surfactant synthesis and a causal relationship was proposed. AimsTo determine whether these apolipoproteins and lipoprotein lipase (LPL) are expressed in the human fetal lung. To compare the distribution patterns of apoC-II and LPL proteins at different developmental ages. Study designReal-time PCR with RNA samples and immunohistochemistry with tissues from lungs of fetuses deceased between 19 and 40weeks' pregnancy. ResultsElevated apolipoprotein A-I (apoA-I), apoA-II, apoC-II, and apoH expression was observed only during a short gestation time window from 32 to 35weeks' gestation. LPL was expressed at relatively constant levels over gestation time. The gene encoding for the essential co-factor of LPL, apoC-II, was expressed at similar levels than LPL gene only during the 32–35week gestation window. ApoC-II and LPL protein distribution vary according to gestation time, with obvious co-localization in capillaries at 32 weeks' gestation, but not in samples collected at 22–24weeks' gestation. ConclusionsApoA-I, apoA-II, apoC-II, and apoH genes are expressed with a human-specific narrow peak of elevated expression in late gestation. Specific and developmental time-dependent distribution profiles were observed for apoC-II and LPL proteins. The 32–35weeks' gestation window, where high levels of expression of apolipoproteins and co-localization of apoC-II and LPL protein were observed, correlates with the reported decrease in the incidence and severity of respiratory distress syndrome (RDS) consequently to the surge of surfactant synthesis.

Hypoxia increases Sca-1/CD44 co-expression in murine mesenchymal stem cells and enhances their adipogenic differentiation potential

Mesenchymal stem cells (MSCs) are usually cultured under normoxic conditions (21% oxygen). However, in vivo, the physiological "niches" for MSCs have a much lower oxygen tension. Because of their plasticity, stem cells are particularly sensitive to their environments, and oxygen tension is one developmentally important stimulus in stem cell biology and plays a role in the intricate balance between cellular proliferation and commitment towards differentiation. Therefore, we investigated here the effect of hypoxia (2% oxygen) on murine adipose tissue (AT) MSC proliferation and adipogenic differentiation. AT cells were obtained from the omental fat and AT-MSCs were selected for their ability to attach to the plastic dishes, and were grown under normoxic and hypoxic conditions. Prior exposure of MSCs to hypoxia led to a significant reduction of ex vivo expansion time, with significantly increased numbers of Sca-1(+) as well as Sca-1(+)/CD44(+)double-positive cells. Under low oxygen culture conditions, the AT-MSC number markedly increased and their adipogenic differentiation potential was reduced. Notably, the hypoxia-mediated inhibition of adipogenic differentiation was reversible: AT-MSCs pre-exposed to hypoxia when switched to normoxic conditions exhibited significantly higher adipogenic differentiation capacity compared to their pre-exposed normoxic-cultured counterparts. Accordingly, the expression of adipocyte-specific genes, peroxisome proliferator activated receptor gamma (Ppargamma), lipoprotein lipase (Lpl) and fatty acid binding protein 4 (Fabp4) were significantly enhanced in hypoxia pre-exposed AT-MSCs. In conclusion, pre-culturing MSCs under hypoxic culture conditions may represent a strategy to enhance MSC production, enrichment and adipogenic differentiation.

Oleuropein enhances osteoblastogenesis and inhibits adipogenesis: the effect on differentiation in stem cells derived from bone marrow

The effects of oleuropein on the processes of osteoblastogenesis and adipogenesis in mesenchymal stem cells (MSCs) from human bone marrow have been studied. We report that oleuropein, a polyphenol abundant in olive tree products, reduces the expression of peroxisome proliferator-activated receptor gamma (PPARγ), inhibits adipocyte differentiation, and enhances differentiation into osteoblast. Age-related bone loss is associated with osteoblast insufficiency during continuous bone remodeling. It has been suggested that the formation of osteoblasts in bone marrow is closely associated with adipogenesis, and age-related changes in this relationship could be responsible for the progressive adiposity of bone marrow which occurs with osteoporosis. In addition, the consumption of oleuropein, a major polyphenol in olive leaves and olive oil, has been associated with a reduction in bone loss. We have analyzed the effects of oleuropein-at concentrations between 10(-6) and 10(-4) M-on the processes of osteoblastogenesis and adipogenesis in MSCs from human bone marrow. The results show an increase in osteoblast differentiation and a decrease in adipocyte differentiation when there is oleuropein in the culture media. The gene expression of osteoblastogenesis markers, RUNXII, osterix, collagen type I, osteocalcin, or alkaline phosphatase (ALP), was higher in osteoblast-induced oleuropein-treated cells. Also, the ALP activity and extracellular matrix mineralization were higher when oleuropein was present in the media. Oleuropein in MSCs induced adipocytes to produce a decrease in the expression of the genes involved in adipogenesis, the PPARγ, lipoprotein lipase, or fatty acid-binding protein 4, and minor fat accumulation. Our data suggest that oleuropein, highly abundant in olive tree products included in the traditional Mediterranean diet, could prevent age-related bone loss and osteoporosis.

The protein function of lipoprotein lipase with Asn291Ser and Lys312insC compound mutation

To study the function of lipoprotein lipase (LPL)with Asn291 Ser and Lys312insC compound mutation in LPL gene knockout heterozygous (LPL~(+/-)) mice. The results showed that triglycerides, free fatty acids, blood glucose and weight of LPL~(+/-) mice were higher than those of c57 mice(P<0. 05). The expressions of LPL Mrna and LPL protein of LPL~(+/-) group were lower than those of c57 group(P<0.05). The injection of Asn291Ser +Lys312insC protein caused little change of the lipid mass and LPL activity,but the injection of normal LPL protein induced obvious decrease of lipid mass and increase of the LPL activity. Key words: Lipoprotein lipase; Gene knockout; Compound mutation

Apolipoprotein A5 and Lipoprotein Lipase Interact to Modulate Anthropometric Measures in Hispanics of Caribbean Origin

Apolipoprotein A5 (APOA5) and lipoprotein lipase (LPL) proteins interact functionally to regulate lipid metabolism, and single-nucleotide polymorphisms (SNPs) for each gene have also been associated independently with obesity risk. Evaluating gene combinations may be more effective than single SNP analyses in identifying genetic risk, but insufficient minor allele frequency (MAF) often limits evaluations of potential epistatic relationships. Populations with multiple ancestral admixtures may provide unique opportunities for evaluating genetic interactions. We examined relationships between LPL m107 (rs1800590) and APOA5 S19W (rs3135506) and lipid and anthropometric measures in Caribbean origin Hispanics (n = 1,019, aged 45-75 years) living in the Boston metropolitan area. Significant interaction terms between LPL m107 and APOA5 S19W were observed for BMI (P = 0.003) and waist circumference (P = 0.019). Higher BMI (P = 0.001), waist (P = 0.011) and hip (P = 0.026) circumference were observed in minor allele (G) carriers for LPL m107 who also carried the APOA5 S19W minor allele (G). Additionally, extreme obesity (BMI > or = 40 kg/m(2)) risk was higher (odds ratio = 4.02; 95% confidence interval: 1.81-8.91; global P = 0.008) for minor allele carriers for both SNPs (LPL TG+GG, APOA5 CG+GG) compared to major allele carriers for both SNPs. In summary, we identified significant interactions for APOA5 S19W and LPL m107 for obesity in Caribbean Hispanics. Population-specific MAFs increase the difficulties of replicating gene-gene interactions, but may support the hypothesis that combinations of frequencies in selected genes could heighten obesity susceptibility in a given population. Analyses of gene-gene interactions may improve understanding of genetically based obesity risk, and underscore the need for further study of groups with multiple ancestral admixtures.