A differentiation program induced by bone morphogenetic proteins 4 and 7 in endodermal epithelial cells provides the molecular basis for efficient nutrient transport by the chicken yolk sac.

BACKGROUND: The mammalian yolk sac provides nutrients for the growing fetus during critical early developmental processes such as neural tube closure, which precedes the functional maturation of the placenta. In contrast, oviparous species such as the chicken rely solely on the yolk sac for transfer of nutrients from the yolk to the developing embryo. However, the molecular mechanisms that provide the yolk sac with nutrient transfer competence remain poorly understood. RESULTS: We demonstrate that the chicken endodermal epithelial cells (EEC), which are in close contact with the yolk, gain their nutrient-transport competence by a paracrine crosstalk with the blood-vessel forming mesodermal cell layer. Bone morphogenetic proteins (BMP) 4 and 7 produced by ectodermal and mesodermal cell layers likely initiate a differentiation program of EECs during the transition from the area vitellina to the area vasculosa. BMPs, by inducing SMAD signaling, promote the up-regulation of endocytic receptor expression and thereby provide the EECs with the molecular machinery to produce triglyceride-rich lipoprotein particles. CONCLUSION: This paracrine signaling cascade may constitute the basis for the EEC-mediated mechanism underlying the efficient uptake, degradation, resynthesis, and transfer of yolk-derived nutrients into the embryonic circulation, which assures proper energy supply and development of the growing fetus.

Circulating soluble LR11, a differentiation regulator for vascular cells, is increased during pregnancy and exaggerated in patients with pre-eclampsia.

BACKGROUND: Pre-eclampsia is a pregnancy-specific disease characterized by onset of hypertension and proteinuria, sometimes progressing into damaging other organs. Here, we investigated the pathological significance of the soluble fragment of LR11 (sLR11), a cell differentiation regulator, in comparison to circulating IL-6 and TNF-α, in pre-eclampsia. METHODS: The study was conducted in a cross-sectional research design with fourteen pre-eclampsia patients and fifty healthy pregnant subjects. Pre-eclampsia was defined as hypertensive disorders in pregnancy at over 20 weeks of gestation with proteinuria. RESULTS: Plasma levels of sLR11 as well as IL-6 in pre-eclampsia were increased compared with those in the healthy pregnant subjects at the first, the second, and the third trimester. Receiver operating characteristic analysis for the detection of pre-eclampsia among third-trimester subjects showed that the areas under the curves of sLR11 and IL-6 were equivalent. sLR11 and IL-6 correlated positively with TNF-α in healthy pregnant subjects. In the pre-eclampsia patients, there was neither a correlation between sLR11 and IL-6 nor between sLR11 and TNF-α. CONCLUSIONS: sLR11 increases during pregnancy, with levels further exaggerated in pre-eclampsia, and may be related to the pathology of pre-eclampsia.

Lipoprotein(a) catabolism: a case of multiple receptors.

Lipoprotein(a) [Lp(a)] is an apolipoprotein B (apoB)-containing plasma lipoprotein similar in structure to low-density lipoprotein (LDL). Lp(a) is more complex than LDL due to the presence of apolipoprotein(a) [apo(a)], a large glycoprotein sharing extensive homology with plasminogen, which confers some unique properties onto Lp(a) particles. ApoB and apo(a) are essential for the assembly and catabolism of Lp(a); however, other proteins associated with the particle may modify its metabolism. Lp(a) specifically carries a cargo of oxidised phospholipids (OxPL) bound to apo(a) which stimulates many proinflammatory pathways in cells of the arterial wall, a key property underlying its pathogenicity and association with cardiovascular disease (CVD). While the liver and kidney are the major tissues implicated in Lp(a) clearance, the pathways for Lp(a) uptake appear to be complex and are still under investigation. Biochemical studies have revealed an exceptional array of receptors that associate with Lp(a) either via its apoB, apo(a), or OxPL components. These receptors fall into five main categories, namely 'classical' lipoprotein receptors, toll-like and scavenger receptors, lectins, and plasminogen receptors. The roles of these receptors have largely been dissected by genetic manipulation in cells or mice, although their relative physiological importance for removal of Lp(a) from the circulation remains unclear. The LPA gene encoding apo(a) has an overwhelming effect on Lp(a) levels which precludes any clear associations between potential Lp(a) receptor genes and Lp(a) levels in population studies. Targeted approaches and the selection of unique Lp(a) phenotypes within populations has nevertheless allowed for some associations to be made. Few of the proposed Lp(a) receptors can specifically be manipulated with current drugs and, as such, it is not currently clear whether any of these receptors could provide relevant targets for therapeutic manipulation of Lp(a) levels. This review summarises the current status of knowledge about receptor-mediated pathways for Lp(a) catabolism.

Soluble LR11 competes with amyloid ß in binding to cerebrospinal fluid-high-density lipoprotein.

BACKGROUND: LR11 is a member of the low-density lipoprotein (LDL) receptor family with high expression in neurons. Some cell surface LR11 is cleaved and secreted into the cerebrospinal fluid (CSF) as soluble LR11 (sLR11). Patients with Alzheimer's disease (AD), particularly apolipoprotein E4 carriers, have high CSF-sLR11 and low CSF-amyloid ß (Aß) concentrations. Therefore, we assessed whether sLR11 is bound to CSF-high-density lipoprotein (HDL) and whether sLR11 competes with Aß in binding to apoE in CSF-HDL. METHODS: We measured CSF-sLR11 concentrations (50 controls and 16 patients with AD) using enzyme immunoassay. sLR11 and apoE distribution in the CSF was evaluated using non-denaturing two-dimensional gel electrophoresis (N-2DGE). ApoE bound to sLR11 or Aß was identified using co-immunoprecipitation assay. RESULTS: CSF-sLR11 concentrations were higher in patients with AD than controls (adjusted for sLR11 using phospholipid). N-2DGE analysis showed that sLR11 and Aß comigrated with a large apoE-containing CSF-HDL. Moreover, fewer apoE was bound to Aß when a higher amount of apoE was bound to sLR11 in patients with AD who presented with ε4/4. CONCLUSION: sLR11 binds to CSF-HDL and competes with Aß in binding to apoE in CSF-HDL, indicating that sLR11 affects Aß clearance via CSF-HDL.

Levels of circulating soluble LR11, a regulator of smooth muscle cell migration, are highly associated with atherosclerotic plaques in patients with carotid artery stenosis.

BACKGROUND: The levels of plasma sLR11, released from intimal SMCs, are positively associated with intima-media thickness (IMT) in asymptomatic subjects. We have evaluated the yet unknown pathological significance of sLR11 for plaque conditions in patients with carotid artery stenosis. METHODS: The presence of LR11 in carotid plaques was investigated using autopsy specimens. A clinical ultrasonography study for elucidating relationships between sLR11 and plaque condition was performed in 46 patients. RESULTS: Immunohistochemistry showed high levels of LR11 in SMCs within thickened intima and at the media-intima border of atherosclerotic carotid plaques. The levels of sLR11 in patients were clearly elevated compared to healthy controls. Univariate analysis of sLR11 revealed significant positive correlation with plaque score and a tendency to correlate with the stenotic fraction. Univariate and multiple regression analyses of plaque scores showed that sLR11, maximum IMT, and HDL-cholesterol independently determined plaque score. Finally, univariate analysis of initial sLR11 levels for changes in imaging markers after one-year follow-up showed that initial sLR11 levels significantly correlated with stenotic fraction progression. CONCLUSIONS: The levels of sLR11, abundantly expressed in carotid atherosclerotic plaques, are highly associated with increased plaque score. sLR11 levels may be predictive of plaque conditions in patients with advanced carotid atherosclerosis.

Lp8 is potentially associated with partial lecithin:cholesterol acyltransferase deficiency in a patient with primary biliary cirrhosis.

BACKGROUND: The significance of Lp8, that is, abnormal lipoprotein(s) detected in fraction 8 by combined high-performance liquid chromatography/gel filtration column in patients with familial lecithin:cholesterol acyltransferase (LCAT) syndrome, in relation to the severity of LCAT deficiency has not been analyzed. OBJECTIVE: We have studied Lp8 in a patient with primary biliary cirrhosis. METHODS: Plasma lipoproteins were analyzed using high-performance liquid chromatography/gel filtration column in the course of treatment of a 47-year-old female patient with primary biliary cirrhosis. RESULTS: Electrophoretic lipoprotein analyses showed massive accumulation of abnormal ß- and preß-lipoproteins with a minor lipoprotein fraction at a position near the cathode corresponding to Lp-X, on day A (status: hypercholesterolemia, LCAT activity undetectable). Chromatographic lipoprotein subfraction analysis revealed free cholesterol- and phospholipid-rich lipoproteins in fractions 1-6, corresponding to chylomicrons and very low-density lipoprotein, and phospholipid- and triglyceride-rich lipoproteins with increased free cholesterol, that is, Lp8, in fractions 7-9 (corresponding to low-density lipoprotein). On day B, after additional treatment for 7 months (status: almost normolipidemia, decreased LCAT activity), although the abnormal lipoprotein and the lipoproteins in fractions 1-6, were drastically decreased, the presence of Lp8 persisted. CONCLUSIONS: Lp8 likely is a minor abnormal lipoprotein fraction in patients with mildly decreased secondary LCAT activity, as well as with severely reduced primary LCAT activity.

Susceptibilities of epicardial and subcutaneous fat tissue for browning-gene expression and diet-induced volume reduction are different.

The upregulation of brown or brown-like beige adipocytes is a potential strategy for the prevention or treatment of diabetes and coronary artery diseases in obese patients. Epicardial adipose tissue (EAT) differs significantly from subcutaneous fat tissue (SAT) in metabolic properties. To investigate properties of EAT further, thermogenesis gene expression was investigated in human autopsy and murine samples, and adipocytes differentiated from EAT mesenchymal cells. Subsequently, analyzed EAT volume alterations were observed to be associated with weight reduction in obese patients by imaging. Gene expression analyses of autopsy samples revealed that UCP­1 mRNA levels in EAT were significantly increased compared with SAT, and ß3­adrenergic receptor (AR) levels tended to be increased; this finding was verified in comparing EAT with SAT in mice. Browning stimulation of human EAT­derived MCs increased uncoupling protein­1 and ß3­AR levels by 3.2 fold­ and 12.6­fold compared with SAT­derived MCs, respectively. Subsequent imaging for EAT volume measurement using multi­detector computed tomography in 10 obese patients revealed that mean EAT volumes did not significantly decrease following weight loss therapy. The EAT volume alterations were not correlated with weight changes, whereas positive correlations were observed in SAT and visceral adipose tissue. Therefore, the studies in man and mouse on EAT properties demonstrated that susceptibilities of EAT and SAT for browning­gene expression and diet­induced volume reduction were grossly different. The data suggest a potential association of EAT with local thermogenetic and metabolic homeostasis in cardiac and/or cardiovascular cells, in conjunction with systemic energy metabolism.

Family-specific aggregation of lipid GWAS variants confers the susceptibility to familial hypercholesterolemia in a large Austrian family.

BACKGROUND AND AIMS: Hypercholesterolemia confers susceptibility to cardiovascular disease (CVD). Both serum total cholesterol (TC) and LDL-cholesterol (LDL-C) exhibit a strong genetic component (heritability estimates 0.41-0.50). However, a large part of this heritability cannot be explained by the variants identified in recent extensive genome-wide association studies (GWAS) on lipids. Our aim was to find genetic causes leading to high LDL-C levels and ultimately CVD in a large Austrian family presenting with what appears to be autosomal dominant inheritance for familial hypercholesterolemia (FH). METHODS: We utilized linkage analysis followed by whole-exome sequencing and genetic risk score analysis using an Austrian multi-generational family with various dyslipidemias, including elevated TC and LDL-C, and one family branch with elevated lipoprotein (a) (Lp(a)). RESULTS: We did not find evidence for genome-wide significant linkage for LDL-C or apparent causative variants in the known FH genes rather, we discovered a particular family-specific combination of nine GWAS LDL-C SNPs (p = 0.02 by permutation), and putative less severe familial hypercholesterolemia mutations in the LDLR and APOB genes in a subset of the affected family members. Separately, high Lp(a) levels observed in one branch of the family were explained primarily by the LPA locus, including short (<23) Kringle IV repeats and rs3798220. CONCLUSIONS: Taken together, some forms of FH may be explained by family-specific combinations of LDL-C GWAS SNPs.

Severely impaired activity of lipoprotein lipase Arg243His is partially ameliorated by emulsifying phospholipids in in vitro triolein hydrolysis analysis.

Background We investigated the in vitro effects of various phospholipids as emulsifiers on the hydrolysing activities of lipoprotein lipase (LPL) Arg243His against triolein as substrate. LPL Arg243His, identified in a patient with hyperchylomicronaemia, displays severely diminished activity for triolein when emulsified with Triton X-100. Methods Lipolytic activities of plasma obtained by heparin injection from a homozygous patient with LPL Arg243His were analysed using triolein emulsified with phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), lysophosphatidylcholine (LPC), or Triton X-100 as substrates. Results The hydrolysing activities of the patient's plasma for triolein emulsified with PC, PE, PS, PI, LPC and Triton X-100 were 9.22 ± 1.06 µmol/ml/h/ngLPL, 2.94 ± 1.60 µmol/ml/h/ng LPL, 3.72 ± 1.63 µmol/ml/h/ng LPL, 3.40 ± 1.20 µmol/ml/h/ngLPL, 3.72 ± 1.96 µmol/ml/h/ngLPL and 7.80 ± 4.48 µmol/ml/h/ng LPL, respectively. Thus, the specific activities of the patient's LPL determined with triolein emulsified with PC were significantly higher than those with PE, PS, PI or LPC as emulsifiers. Relative to the activities of normal plasma measured with PC, PE, PS, PI and LPC as emulsifiers, the mutant's activities were 49.1 ± 5.2%, 44.1 ± 5.7%, 31.7 ± 12.6%, 19.2 ± 6.9% and 23.8 ± 11.3%, respectively. Using PC, PE, PS, PI and LPC as emulsifiers, the mutant's activities for triolein-lipolysis relative to normal were significantly increased in comparison to the relative activity measured with the classical emulsifier, Triton X-100 (12.9 ± 6.7%). Conclusions Impaired triolein hydrolysis by LPL Arg243His was partially ameliorated by triolein emulsification with phospholipids. The in vitro analysis of triolein hydrolysis using various phospholipid emulsifiers may be useful for the further understanding of impaired LPL function.

Levels of the soluble LDL receptor-relative LR11 decrease in overweight individuals with type 2 diabetes upon diet-induced weight loss.

BACKGROUND AND AIMS: Cardiovascular disease (CVD) is a major complication in patients with type 2 diabetes (T2D), especially in those with obesity. Plasma soluble low density lipoprotein receptor-relative with 11 ligand-binding repeats (sLR11) plays a role in the development of atherosclerosis and has been linked to the metabolism of triglyceride-rich lipoproteins, adiposity, and vascular complications in T2D. We aimed to determine the effect of diet-induced weight loss on plasma sLR11 levels in overweight and obese individuals with T2D. METHODS: Plasma sLR11 levels were determined in 64 individuals with T2D and BMI >27 kg/m2 before and after a 20-week weight loss diet. As a reference, sLR11 levels were also determined in 64 healthy, non-obese controls, matched as a group for age and sex. RESULTS: Median plasma sLR11 levels of the T2D study-group at baseline (15.4 ng/mL (IQR 12.9-19.5)) were higher than in controls (10.2 (IQR: 8.7-12.2) ng/mL; p = 0.001). The diet resulted in a weight loss of 9.7 ± 5.2% (p = 0.001) and improved CVD risk factors. sLR11 levels were reduced to 13.3 ng/mL (IQR 11.0-17.1; p = 0.001). Changes in sLR11 levels positively associated with changes in non-HDL cholesterol (B = 1.54, R2 = 0.17, p = 0.001) and HbA1c (B = 0.07, R2 = 0.11, p = 0.007), but not with weight loss (B = 0.04, R2 = 0.05, p = 0.076). The changes in non-HDL cholesterol and HbA1c together explained 24% of the variance of sLR11 reduction (p = 0.001). CONCLUSIONS: Weight loss dieting in overweight and obese individuals with T2D resulted in a reduction in plasma sLR11 levels that was associated with improvements in lipid-profile and glycemic state.

Levels of soluble LR11/SorLA are highly increased in the bile of patients with biliary tract and pancreatic cancers.

BACKGROUND: The utility of molecules derived from cancer cells as biomarkers of the pathological status in biliary tract and pancreatic cancers is still limited. Soluble LDL receptor relative with 11 ligand-binding repeats (sLR11), a molecule released from immature cells, has been shown to be a circulating biomarker for early stage hematological malignancies. METHODS: We have evaluated the pathological significance of bile sLR11 levels in 147 samples from 72 patients with biliary tract cancer (BTC), pancreatic cancer (PC), or benign diseases. RESULTS: The bile sLR11 levels in the cancer patients were significantly increased compared with those in patients without cancer, independent of cytological detection of cancer cells in bile. The average bile sLR11 levels in cancer patients were significantly higher than in those with benign diseases, while levels of bile carbohydrate antigen 19-9 (CA19-9) and carcinoembryonic antigen (CEA) were not different. LR11 protein was found to be highly expressed in the BTC and PC cells. The LR11 transcript levels in cholangiocarcinoma and pancreatic cancer cell lines were sharply induced during proliferation and significantly increased under hypoxic conditions. CONCLUSIONS: Therefore, sLR11 levels in bile may be indicative of cancer cell conditions and may serve as potential novel biomarker in patients with BTC and PC.

Circulating soluble form of LR11, a regulator of smooth muscle cell migration, is a novel marker for intima-media thickness of carotid arteries in type 2 diabetes.

BACKGROUND: Smooth muscle cell (SMC) migration from the media to the intima, a process affecting plaque stability in advanced-stage atherosclerosis, is under the control of LR11. To delineate the clinical significance of the circulating soluble form of LR11 (sLR11) in patients with type 2 diabetes (T2D), we analyzed the correlation of sLR11 levels with intima-media thickness (IMT) of carotid arteries. METHODS: Plasma sLR11 levels were measured in 165 patients with T2D (mean age 56.2±10.4 y, 58.2% males, and BMI 24.6±3.6) by ELISA. Averaged IMT levels of common carotid arteries were determined by ultrasonography. RESULTS: Circulating sLR11 levels were 9.8±3.5ng/ml, and correlated positively with the classical atherosclerosis risk factors age, sex, systolic blood pressure, low-density lipoprotein-cholesterol (LDL-C), fasting plasma-glucose (FPG), and glycosylated hemoglobin. Multivariate linear regression analysis indicated that only FPG was associated with sLR11; sLR11 correlated positively with IMT, together with age and FPG, but less with LDL-C. Among the serum risk factors for IMT, multivariate linear regression analysis uncovered that sLR11 was independently associated with IMT. Subsequent logistic analysis revealed that FPG correlated best with IMT values at a cut-off of 0.80mm and sLR11 at a cut-off of 0.90mm, respectively, while LDL-C showed lower discriminatory power at any IMT cut-off values. CONCLUSION: Increased sLR11 concentrations are highly associated with increased IMT as well as with FPG in middle-aged, non-obese patients with T2D. Circulating sLR11 may be a novel marker representing the pathophysiology of intimal SMCs in patients with T2D.

Hepatosteatosis and estrogen increase apolipoprotein O production in the chicken.

Apolipoprotein O (ApoO) is a recently discovered plasma apolipoprotein that may also play a role in the mitochondrial inner membrane. Possibly due to this complexity, its physiological functions have not been elucidated yet. To gain insight from a non-mammalian experimental system, we have investigated the regulation of ApoO levels in an alternative, well-suited model for studies on lipid metabolism, the chicken. qPCR using specific primer pairs and Western blot analysis with our rabbit anti-chicken ApoO antiserum demonstrated ApoO in the liver of chickens fed a control or a fat-enriched diet, as well as in 2 chicken hepatoma cell lines, LMH cells and the estrogen-responsive LMH-2A cells, under conditions of lipid loading by incubation with BSA-complexed oleic acid. Induced triglyceride accumulation in both the liver and the hepatic cells was associated with significantly increased levels of ApoO mRNA and protein. Furthermore, upon treatment for 24 h with estrogen of the estrogen receptor-expressing LMH-2A cells, quantitative analysis of ApoO transcripts and Western blotting revealed increases of ApoO expression. Finally, upon a single administration of estrogen to roosters that leads to hyperlipidemia, higher hepatic levels of both ApoO transcript and protein were observed within 24 h. Based on these data, we propose that hepatic expression of ApoO is tightly linked not only to diet-induced hepatosteatosis, but also to increased lipoprotein-production induced by, e.g., hormones. The findings support a role of ApoO as an effector of compromised mitochondrial function that likely accompanies the onset of non-alcoholic fatty liver disease.

A comparative study of vitellogenesis in Echinodermata: Lessons from the sea star.

The provision of yolk precursor proteins to the oviparous egg is crucial for normal embryo development. In Echinodermata, a transferrin-like yolk component termed major yolk protein (MYP) is a major precursor protein in Echinoidea and Holothuroidea. In contrast, in Asteroidea a single vitellogenin (Vtg) was recently identified, but its role as primary yolk protein remains unclear. To resolve the apparent MYP-Vtg dichotomy in sea stars and to understand the dynamics of candidate yolk protein gene expression during the reproductive cycle, we investigated the molecular structures of sea star Vtg and MYP and quantified their transcript levels during oogenesis. By combining protein sequencing of the predominant proteins in ovulated eggs of Patiriella regularis with ovarian transcriptome sequencing and molecular cloning, we characterized two cDNAs encoding two bona fide Vtgs (PrVtg1 and PrVtg2) and a partial cDNA encoding MYP (PrMYP). PrMYP mRNA was found in low abundance in growing oocytes, possibly as maternal transcripts for translation after ovulation. In contrast, PrVtg transcripts, whose levels varied during the reproductive cycle, were not found in developing oocytes - rather, they were detected in ovarian follicle cells and pyloric caeca, indicating an extra-oocytic origin. Vtg accumulating in oocytes was stored in the form of cleaved products, which constituted the most abundant yolk polypeptides in ovulated sea star eggs; their levels decreased during early embryonic and larval development. Together, these traits are the hallmarks of a classical yolk protein - and hence, we contend that Vtg, and not MYP, is the main yolk protein in asteroids.

Subfraction analysis of circulating lipoproteins in a patient with Tangier disease due to a novel ABCA1 mutation.

Tangier disease, characterized by low or absent high-density lipoprotein (HDL), is a rare hereditary lipid storage disorder associated with frequent, but not obligatory, severe premature atherosclerosis due to disturbed reverse cholesterol transport from tissues. The reasons for the heterogeneity in atherogenicity in certain dyslipidemias have not been fully elucidated. Here, using high-performance liquid chromatography with a gel filtration column (HPLC-GFC), we have studied the lipoprotein profile of a 17-year old male patient with Tangier disease who to date has not developed manifest coronary atherosclerosis. The patient was shown to be homozygous for a novel mutation (Leu1097Pro) in the central cytoplasmic region of ATP-binding cassette transporter A1 (ABCA1). Serum total and HDL-cholesterol levels were 59mg/dl and 2mg/dl, respectively. Lipoprotein electrophoretic analyses on agarose and polyacrylamide gels showed the presence of massively abnormal lipoproteins. Further analysis by HPLC-GFC identified significant amounts of lipoproteins in low-density lipoprotein (LDL) subfractions. The lipoprotein particles found in the peak subfraction were smaller than normal LDL, were rich in triglycerides, but poor in cholesterol and phospholipids. These findings in an adolescent Tangier patient suggest that patients in whom these triglyceride-rich, cholesterol- and phospholipid-poor LDL-type particles accumulate over time, would experience an increased propensity for developing atherosclerosis.

Lipid droplets in activated mast cells - a significant source of triglyceride-derived arachidonic acid for eicosanoid production.

Mast cells are potent effectors of immune reactions and key players in various inflammatory diseases such as atherosclerosis, asthma, and rheumatoid arthritis. The cellular defense response of mast cells represents a unique and powerful system, where external signals can trigger cell activation resulting in a stimulus-specific and highly coordinated release of a plethora of bioactive mediators. The arsenal of mediators encompasses preformed molecules stored in cytoplasmic secretory granules, as well as newly synthesized proteinaceous and lipid mediators. The release of mediators occurs in strict chronological order and requires proper coordination between the endomembrane system and various enzymatic machineries. For the generation of lipid mediators, cytoplasmic lipid droplets have been shown to function as a major intracellular pool of arachidonic acid, the precursor for eicosanoid biosynthesis. Recent studies have revealed that not only phospholipids in mast cell membranes, but also triglycerides in mast cell lipid droplets are a substrate source for eicosanoid formation. The present review summarizes current knowledge about mast cell lipid droplet biology, and discusses expansions and challenges of traditional mechanistic models for eicosanoid production.

Lipid transport to avian oocytes and to the developing embryo.

Studies of receptor-mediated lipoprotein metabolic pathways in avian species have revealed that physiological intricacies of specific cell types are highly analogous to those in mammals. A prime example for the power of comparative studies across different animal kingdoms, elucidated in the chicken, is that the expression of different lipoprotein receptors in somatic cells and oocytes are the key to oocyte growth. In avian species, yolk precursor transport from the hen's liver to rapidly growing oocytes and the subsequent transfer of yolk nutrients via the yolk sac to the developing embryo are highly efficient processes. Oocytes grow from a diameter of 5 mm to 2.5-3 cm in only 7 days, and the yolk sac transfers nutrients from the yolk stored in the mature oocyte to the embryo within just 2 weeks. The underlying key transport mechanism is receptor-mediated endocytosis of macromolecules, i.e., of hepatically synthesized yolk precursors for oocyte growth, and of mature yolk components for embryo nutrition, respectively. Recently, the receptors involved, as well as the role of lipoprotein synthesis in the yolk sac have been identified. As outlined here, lipoprotein degradation/resynthesis cycles and the expression of lipoprotein receptors are not only coordinated with the establishment of the follicular architecture embedding the oocyte, but also with the generation of the yolk sac vasculature essential for nutrient transfer to the embryo.

Soluble LR11/SorLA represses thermogenesis in adipose tissue and correlates with BMI in humans.

Thermogenesis in brown adipose tissue (BAT) is an important component of energy expenditure in mammals. Recent studies have confirmed its presence and metabolic role in humans. Defining the physiological regulation of BAT is therefore of great importance for developing strategies to treat metabolic diseases. Here we show that the soluble form of the low-density lipoprotein receptor relative, LR11/SorLA (sLR11), suppresses thermogenesis in adipose tissue in a cell-autonomous manner. Mice lacking LR11 are protected from diet-induced obesity associated with an increased browning of white adipose tissue and hypermetabolism. Treatment of adipocytes with sLR11 inhibits thermogenesis via the bone morphogenetic protein/TGFß signalling pathway and reduces Smad phosphorylation. In addition, sLR11 levels in humans are shown to positively correlate with body mass index and adiposity. Given the need for tight regulation of a tissue with a high capacity for energy wastage, we propose that LR11 plays an energy conserving role that is exaggerated in states of obesity.

LR11/SorLA links triglyceride-rich lipoproteins to risk of developing cardiovascular disease in FH patients.

OBJECTIVE: Familial Hypercholesterolemia (FH) is associated with an increased risk of cardiovascular disease (CVD). However, whether an individual heterozygous FH patient will develop CVD depends on other genetic- and environmental risk factors as well. LDL receptor-related protein with 11 ligand binding repeat (LR11) and its soluble form (sLR11) play a role in the progression of atherosclerosis. We investigated the involvement of LR11 and sLR11 in CVD development in FH patients and in LDLR deficient (Ldlr(-/-)) mice. APPROACH AND RESULTS: In statin-treated asymptomatic male heterozygous FH subjects, plasma sLR11 levels correlated with carotid intima-media thickness. Increased plasma sLR11 levels were found in Ldlr(-/-) and also in wild-type mice exclusively after high-fat feeding. Hepatic LR11 mRNA levels, however, were higher in chow-fed Ldlr(-/-) in comparison with wild-type mice and were further increased after a high fat diet. Similar results were obtained with Apoe(-/-) mice, but not with wild-type mice. LR11 mRNA and protein levels and release of sLR11 from cultured HepG2 and aortic smooth muscle cells were upregulated by postprandial triglyceride-rich lipoproteins (TGRL). Overexpression of human LR11 in CHO cells resulted in increased binding and association of 12I-labeled TGRL, but not of 12I-labeled LDL. CONCLUSION: Our data strongly suggest an involvement of LR11 in mediating the harmful effects of a high-fat diet on CVD progression. Elevated sLR11 levels may increase the CVD risk especially in subjects with delayed clearance of triglyceride-rich remnants, such as in FH patients.

Estrogen enhances secretion of apolipoprotein B-100 containing lipoproteins by BeWo cells.

Although the early human embryo is capable of covering its cholesterol demand by endogenous synthesis, during later stages of development the fetus may become dependent on transplacental cholesterol transport. On one hand, this conclusion is based on the severe developmental abnormalities of embryos with mutations in the gene specifying the enzyme catalyzing the last step of cholesterol synthesis, 7-dehydrocholesterol reductase, causing Smith-Lemli-Opitz Syndrome. On the other hand, increased total maternal plasma cholesterol levels may reflect the requirement by the growing fetus and/or the placenta for cholesterol. Various molecules and complexes must cross the placental barrier consisting of trophoblasts and fetal endothelial cells to reach the fetal circulation. The de novo synthesis of apolipoprotein B (apoB)-containing lipoproteins coupled to secretion from trophoblasts towards the fetal side is one efficient pathway for cholesterol supply. ApoB and the microsomal triglyceride transfer protein (MTP) are essential components for the assembly of apoB-containing lipoproteins. The aim of this study was to evaluate functional properties of the human placental cell line BeWo as an in vitro model for placental synthesis of apoB-containing lipoproteins by focusing on components required for lipoprotein assembly and secretion. We demonstrate mRNA and protein production of apoB-100, MTP, and protein disulfide isomerase (PDI) in BeWo cells. In addition, metabolic radiolabeling and apoB-immunoprecipitation of cell extracts and media revealed that synthesis and secretion of apoB-containing lipoproteins are enhanced by estrogen. The expression of apoB-100, MTP, and PDI, and the estrogen-stimulated lipoprotein secretion by BeWo cells suggest that these cells are a useful system to study aspects of lipoprotein metabolism at the placental barrier.