Identification of the bovine cholesterol efflux regulatory protein ABCA1 and its expression in various tissues1

Non-Cholesterol Sterols in Breast Milk and Risk of Allergic Outcomes in the First Two Years of Life

This study aimed to explore associations between non-cholesterol sterol concentrations in breast milk and allergic outcomes in children aged two. Data from the KOALA Birth Cohort Study, the Netherlands, were used. Non-cholesterol sterols were analyzed by gas–liquid chromatography–mass spectrometry in breast milk sampled one-month postpartum (N = 311). Sterols were selected for each allergic outcome, i.e., eczema, wheeze, and allergic sensitization, prior to analyses. Associations between the selected sterols with allergic outcomes were analyzed using multiple logistic regression to calculate odds ratios (ORs). The odds of eczema in the first two years of life were lower with higher concentrations of cholestanol (OR (95%CI): 0.98 (0.95; 1.00), p = 0.04), lanosterol (0.97 (0.95; 1.00), p = 0.02), lathosterol (0.93 (0.87; 0.99), p = 0.02), and stigmasterol (0.51 (0.29; 0.91), p = 0.02) in breast milk sampled one-month postpartum. None of the sterols were associated with wheeze in the first two years of life. The odds of allergic sensitization at age two were lower with higher concentrations of campesterol in breast milk (OR (95%CI): 0.81 (0.70; 0.95), p = 0.01). In conclusion, our data suggest that exposure to higher non-cholesterol sterol concentrations in breast milk may indeed be associated with the prevention of allergic outcomes in the first two years of life.

The Physiological Roles of Vitamin E and Hypovitaminosis E in the Transition Period of High-Yielding Dairy Cows

Simple Summary

In high-yield cows, most production diseases occur during transition periods. Alpha-tocopherol, the most biologically active form of vitamin E, declines in blood and reaches the lowest levels (hypovitaminosis E) around calving. Hypovitaminosis E is associated with the incidence of peripartum diseases. Therefore, many studies which have been published for more than 30 years have investigated the effects of α-tocopherol supplementation. This α-tocopherol deficiency was thought to be caused by complex factors. However, until recently, the physiological factors or pathways underlying hypovitaminosis E in the transition period have been poorly understood. In the last 10 years, the α-tocopherol-related genes expression, which regulate the metabolism, transportation, and tissue distribution of α-tocopherol in humans and rodents, has been reported in ruminant tissues. In this paper, we discuss at least six physiological phenomena that occur during the transition period and may be candidate factors predisposing to a decreased blood α-tocopherol level and hypovitaminosis E with changes in α-tocopherol-related genes expression.

Abstract

Levels of alpha-tocopherol (α-Toc) decline gradually in blood throughout prepartum, reaching lowest levels (hypovitaminosis E) around calving. Despite numerous reports about the disease risk in hypovitaminosis E and the effect of α-Toc supplementation on the health of transition dairy cows, its risk and supplemental effects are controversial. Here, we present some novel data about the disease risk of hypovitaminosis E and the effects of α-Toc supplementation in transition dairy cows. These data strongly demonstrate that hypovitaminosis E is a risk factor for the occurrence of peripartum disease. Furthermore, a study on the effectiveness of using serum vitamin levels as biomarkers to predict disease in dairy cows was reported, and a rapid field test for measuring vitamin levels was developed. By contrast, evidence for how hypovitaminosis E occurred during the transition period was scarce until the 2010s. Pioneering studies conducted with humans and rodents have identified and characterised some α-Toc-related proteins, molecular players involved in α-Toc regulation followed by a study in ruminants from the 2010s. Based on recent literature, the six physiological factors: (1) the decline in α-Toc intake from the close-up period; (2) changes in the digestive and absorptive functions of α-Toc; (3) the decline in plasma high-density lipoprotein as an α-Toc carrier; (4) increasing oxidative stress and consumption of α-Toc; (5) decreasing hepatic α-Toc transfer to circulation; and (6) increasing mammary α-Toc transfer from blood to colostrum, may be involved in α-Toc deficiency during the transition period. However, the mechanisms and pathways are poorly understood, and further studies are needed to understand the physiological role of α-Toc-related molecules in cattle. Understanding the molecular mechanisms underlying hypovitaminosis E will contribute to the prevention of peripartum disease and high performance in dairy cows.

MicroRNA-33a-5p sponges to inhibit pancreatic β-cell function in gestational diabetes mellitus LncRNA DANCR

BACKGROUND

Gestational diabetes mellitus (GDM) is the most common medical complication associated with pregnancy, which may impose risks on both mother and fetus. Micro RNAs (miRNAs) and long noncoding RNAs (lncRNAs) are implied as vital regulators in GDM. A recent paper revealed dysregulation of miR-33a-5p in placental tissues of GDM patients. However, the biological function of miR-33a-5p in GDM remains elusive. This study focused on exploring the function and underlying mechanisms of miR-33a-5p in GDM.

METHODS

12 GDM pregnancies and 12 healthy pregnancies were enrolled in the study. INS-1 cell line was applied in in vitro experiments. The expression levels of miR-33a-5p, lnc-DANCR (Differentiation Antagonizing Non-Protein Coding RNA), and ABCA1 (ATP-binding cassette transporter 1) mRNA were determined by RT-qPCR assay. Glucose and insulin levels were measured by ELISA assay. Luciferase reporter assay and western blot assay were applied to validate the target of miR-33a-5p.

RESULTS

miR-33a-5p was upregulated in the blood samples from GDM, and was positively correlated with blood glucose (p < 0.0001). Overexpression or inhibition of miR-33a-5p significantly inhibited or promoted cell growth and insulin production of INS-1 cells (p < 0.01). Furthermore, ABCA1 is a direct target of miR-33a-5p, and lnc-DANCR functions as a sponge for miR-33a-5p to antagonize the function of miR-33a-5p in INS-1 cells.

CONCLUSION

Our study demonstrated that lnc-DANCR-miR-33a-5p-ABCA1 signaling cascade plays a crucial role in the regulation of the cellular function of INS-1 cells.

Plant-based sterols and stanols in health & disease: "Consequences of human development in a plant-based environment?"

Dietary plant sterols and stanols as present in our diet and in functional foods are well-known for their inhibitory effects on intestinal cholesterol absorption, which translates into lower low-density lipoprotein cholesterol concentrations. However, emerging evidence suggests that plant sterols and stanols have numerous additional health effects, which are largely unnoticed in the current scientific literature. Therefore, in this review we pose the intriguing question "What would have occurred if plant sterols and stanols had been discovered and embraced by disciplines such as immunology, hepatology, pulmonology or gastroenterology before being positioned as cholesterol-lowering molecules?" What would then have been the main benefits and fields of application of plant sterols and stanols today? We here discuss potential effects ranging from its presence and function intrauterine and in breast milk towards a potential role in the development of non-alcoholic steatohepatitis (NASH), cardiovascular disease (CVD), inflammatory bowel diseases (IBD) and allergic asthma. Interestingly, effects clearly depend on the route of entrance as observed in intestinal-failure associated liver disease (IFALD) during parenteral nutrition regimens. It is only until recently that effects beyond lowering of cholesterol concentrations are being explored systematically. Thus, there is a clear need to understand the full health effects of plant sterols and stanols.

ATP-binding cassette transporters in reproduction: a new frontier

BACKGROUND

The transmembrane ATP-binding cassette (ABC) transporters actively efflux an array of clinically relevant compounds across biological barriers, and modulate biodistribution of many physiological and pharmacological factors. To date, over 48 ABC transporters have been identified and shown to be directly and indirectly involved in peri-implantation events and fetal/placental development. They efflux cholesterol, steroid hormones, vitamins, cytokines, chemokines, prostaglandins, diverse xenobiotics and environmental toxins, playing a critical role in regulating drug disposition, immunological responses and lipid trafficking, as well as preventing fetal accumulation of drugs and environmental toxins.

METHODS

This review examines ABC transporters as important mediators of placental barrier functions and key reproductive processes. Expression, localization and function of all identified ABC transporters were systematically reviewed using PubMed and Google Scholar websites to identify relevant studies examining ABC transporters in reproductive tissues in physiological and pathophysiological states. Only reports written in English were incorporated with no restriction on year of publication. While a major focus has been placed on the human, extensive evidence from animal studies is utilized to describe current understanding of the regulation and function of ABC transporters relevant to human reproduction.

RESULTS

ABC transporters are modulators of steroidogenesis, fertilization, implantation, nutrient transport and immunological responses, and function as 'gatekeepers' at various barrier sites (i.e. blood-testes barrier and placenta) against potentially harmful xenobiotic factors, including drugs and environmental toxins. These roles appear to be species dependent and change as a function of gestation and development. The best-described ABC transporters in reproductive tissues (primarily in the placenta) are the multidrug transporters p-glycoprotein and breast cancer-related protein, the multidrug resistance proteins 1 through 5 and the cholesterol transporters ABCA1 and ABCG1.

CONCLUSIONS

The ABC transporters have various roles across multiple reproductive tissues. Knowledge of efflux direction, tissue distribution, substrate specificity and regulation of the ABC transporters in the placenta and other reproductive tissues is rapidly expanding. This will allow better understanding of the disposition of specific substrates within reproductive tissues, and facilitate development of novel treatments for reproductive disorders as well as improved approaches to protecting the developing fetus.

siRNA as a tool to improve the treatment of brain diseases: Mechanism, targets and delivery

As the population ages, brain pathologies such as neurodegenerative diseases and brain cancer increase their incidence, being the need to find successful treatments of upmost importance. Drug delivery to the central nervous system (CNS) is required in order to reach diseases causes and treat them. However, biological barriers, mainly blood-brain barrier (BBB), are the key obstacles that prevent the effectiveness of possible treatments due to their ability to strongly limit the perfusion of compounds into the brain. Over the past decades, new approaches towards overcoming BBB and its efflux transporters had been proposed. One of these approaches here reviewed is through small interfering RNA (siRNA), which is capable to specifically target one gene and silence it in a post-transcriptional way. There are different possible functional proteins at the BBB, as the ones responsible for transport or just for its tightness, which could be a siRNA target. As important as the effective silence is the way to delivery siRNA to its anatomical site of action. This is where nanotechnology-based systems may help, by protecting siRNA circulation and providing cell/tissue-targeting and intracellular siRNA delivery. After an initial overview on incidence of brain diseases and basic features of the CNS, BBB and its efflux pumps, this review focuses on recent strategies to reach brain based on siRNA, and how to specifically target these approaches in order to treat brain diseases.

Cholesterol transport and regulation in the mammary gland

The milk-producing alveolar epithelial cells secrete milk that remains after birth the principal source of nutrients for neonates. Milk secretion and composition are highly regulated processes via integrated actions of hormones and local factors which involve specific receptors and downstream signal transduction pathways. Overall milk composition is similar among mammalian species, although the content of individual constituents such as lipids may significantly differ from one species to another. The milk lipid fraction is essentially composed of triglycerides, which represent more than 95 % of the total lipids in human and commercialized bovine milk. Though sterols, including cholesterol, which is the major milk sterol, represent less than 0.5 % of the total milk lipid fraction, they are of key importance for several biological processes. Cholesterol is required for the formation of biological membranes especially in rapidly growing organisms, and for the synthesis of sterol-based compounds. Cholesterol found in milk originates predominantly from blood uptake and, to a certain extent, from local synthesis in the mammary tissue. The present review summarizes current knowledge on cellular mechanisms and regulatory processes determining intra- and transcellular cholesterol transport in the mammary gland. Cholesterol exchanges between the blood, the mammary alveolar cells and the milk, and the likely role of active cholesterol transporters in these processes are discussed. In this context, the hormonal regulation and signal transduction pathways promoting active cholesterol transport as well as potential regulatory crosstalks are highlighted.

Effects of rapeseed and soybean oil dietary supplementation on bovine fat metabolism, fatty acid composition and cholesterol levels in milk

The main goal of this experiment was to study the effect of milk fat depression, induced by supplementing diet with plant oils, on the bovine fat metabolism, with special interest in cholesterol levels. For this purpose 39 cows were divided in three groups and fed different rations: a control group (C) without any oil supplementation and two groups with soybean oil (SO) or rapeseed oil (RO) added to the partial mixed ration (PMR). A decrease in milk fat percentage was observed in both oil feedings with a higher decrease of -1·14 % with SO than RO with -0·98 % compared with the physiological (-0·15 %) decline in the C group. There was no significant change in protein and lactose yield. The daily milk cholesterol yield was lower in both oil rations than in control ration, while the blood cholesterol level showed an opposite variation. The milk fatty acid pattern showed a highly significant decrease of over 10 % in the amount of saturated fatty acids (SFA) in both oil feedings and a highly significant increase in mono (MUFA) and poly (PUFA) unsaturated fatty acids, conjugated linoleic acids (CLA) included. The results of this experiment suggest that the feeding of oil supplements has a high impact on milk fat composition and its significance for human health, by decreasing fats with a potentially negative effect (SFA and cholesterol) while simultaneously increasing others with positive (MUFA, PUFA, CLA).

Polyunsaturated fatty acid-enriched diets used for the treatment of canine chronic enteropathies decrease the abundance of selected genes of cholesterol homeostasis

Lipids are important for cell function and survival, but abnormal concentrations may lead to various diseases. Cholesterol homeostasis is greatly dependent on the active transport by membrane proteins, whose activities coordinate lipid status with cellular function. Intestinal Niemann-Pick C1-Like 1 protein (NPC1L1) and scavenger receptor B1 (SR-B1) participate in the uptake of extracellular cholesterol, whereas ATP binding cassette A1 (ABCA1) mediates the efflux of excessive intracellular cholesterol. Caveolin-1 binds cholesterol and fatty acids (FA) and participates in cholesterol trafficking. Sterol response element binding protein-2 (SREBP-2) is a sensor that regulates intracellular cholesterol synthesis. Given that cholesterol is a constituent of chylomicrons, whose synthesis is enhanced with an increased FA supply, we tested the hypothesis that feeding polyunsaturated FA (PUFA)-enriched diets in treatment of canine chronic enteropathies alters the mRNA expression of genes involved in cholesterol homeostasis. Using quantitative reverse transcriptase polymerase chain reaction (RT-PCR), we compared the mRNA abundance of NPC1L1, SR-B1, ABCA1, caveolin-1, and SREBP-2 in duodenal mucosal biopsies of dogs with food-responsive diarrhea (FRD; n=14) and inflammatory bowel disease (IBD; n=7) before and after treatment with cholesterol-free PUFA-enriched diets and in healthy controls (n=14). The abundance of caveolin-1, ABCA1, and SREBP-2 were altered by PUFA-enriched diets (P<0.05), whereas that of NPC1L1 and SR-B1 mRNA remained unchanged. The gene expression of caveolin-1, ABCA1, and SREBP-2 was down-regulated (P<0.05) by PUFA-enriched diets in IBD dogs only. Our results suggest that feeding PUFA-enriched diets may alter cholesterol homeostasis in duodenal mucosal cells of dogs suffering from IBD.

Rapid method for cholesterol analysis in bovine milk and options for applications

The adaptation of a colorimetric technique for the analysis of cholesterol in raw milk is presented. Performance quality was satisfying (mean intra-assay coefficient of variation (CV) 4·8, inter-assay CV 9·1%, linearity between 0 and 7 mm, recovery of spiked cholesterol into raw milk 98·1 and 106·3%). However, the milk fat extraction must be carried out within the 48 hours following milk sampling. When performing sampling, the significant variation of milk cholesterol composition during the milking process has to be taken into account.

Endurance training enhances ABCA1 expression in rat small intestine

The purpose of this study was to investigate liver and intestinal ABCA1 expression and plasma HDL-C level in response to treadmill-running training in rats. Twenty adult Wistar male rats (17-18 weeks old, 300-322 g) were divided into control (n = 10) and Training (n = 10) groups. Training group trained at 25 m/min (0% grade) for 60 min/day, 5 days/week for 12 weeks. Rats were killed 48 h after the last session of training. The intestinal and liver ABCA1 mRNA expression was found to be significantly higher in trained compared to control group (P < 0.006 and P < 0.024, respectively). Intestine and liver ATP concentrations remained unchanged. Plasma HDL-C, HDL2-C, Apo A-1, pre-beta HDL-C concentration, LCAT activity, TC/HDL-C and LDL-C/HDL-C ratio significantly increased in trained group (P < 0.01, P < 0.006, P < 0.001, P < 0.001 P < 0.067, P < 0.02, and P < 0.03, respectively). However, other lipoprotein concentrations were unchanged. In conclusion, we found that endurance training induced significant elevation in plasma HDL-C and HDL2-C concentrations, accompanied by higher plasma Apo A-1, pre-beta HDL-C concentrations, LCAT activity and ABCA1 mRNA expressions in rat intestine, and liver.

Cyclosporine stimulates the renal epithelial sodium channel by elevating cholesterol

Cyclosporine A (CsA) is an efficient immunosuppressant used for reducing allograft rejection but with a severe side effect of causing hypertension. We hypothesize that the renal epithelial sodium channel (ENaC) may participate in CsA-induced hypertension. In the present study, we used the patch-clamp cell-attached configuration to examine whether and how CsA stimulates ENaC in A6 distal nephron cells. The data showed that CsA significantly increased ENaC open probability. Since CsA is an inhibitor of the ATP-binding cassette A1 (ABCA1) transporter, we employed 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), another ABCA1 inhibitor, and found that DIDS mimicked the effects of CsA on ENaC basal and cholesterol-induced activity but without any additive effect if combined with CsA. CsA and DIDS also had an identical effect on reduced ENaC activity caused by cholesterol extraction. ABCA1 protein was detected in A6 cells by Western blot analysis. Confocal microscopy data showed that both CsA and DIDS facilitated A6 cells to uptake cholesterol. Since enhanced ENaC activity is known to cause hypertension, these data together suggest that CsA may cause hypertension by stimulating ENaC through a pathway associated with inhibition of ABCA1 and consequent elevation of cholesterol in the cells.

Differential expression of ABC transporters and their regulatory genes during lactation and dry period in bovine mammary tissue

ATP-binding cassette (ABC) transporters play a pivotal role in human physiology, and mutations in these genes often result in severe hereditary diseases. ABC transporters are expressed in the bovine mammary gland but their physiological role in this organ remains elusive. Based on findings in the context of human disorders we speculated that candidate ABC transporters are implicated in lipid and cholesterol transport in the mammary gland. Therefore we investigated the expression pattern of selected genes that are associated with sterol transport in lactating and nonlactating mammary glands of dairy cows. mRNA levels from mammary gland biopsies taken during lactation and in the first and second week of the dry period were analysed using quantitative PCR. Five ABC transporter genes, namely ABCA1, ABCA7, ABCG1, ABCG2 and ABCG5, their regulating genes LXRalpha, PPARgamma, SREBP1 and the milk proteins lactoferrin and alpha-lactalbumin were assessed. A significantly enhanced expression in the dry period was observed for ABCA1 while a significant decrease of expression in this period was detected for ABCA7, ABCG2, SREBP1 and alpha-lactalbumin. ABCG1, ABCG5, LXRalpha, PPARgamma and lactoferrin expression was not altered between lactation and dry period. These results indicate that candidate ABC transporters involved in lipid and cholesterol transport show differential mRNA expression between lactation and the dry period. This may be due to physiological changes in the mammary gland such as immigration of macrophages or the accumulation of fat due to the loss of liquid in the involuting mammary gland. The current mRNA expression analysis of transporters in the mammary gland is the prerequisite for elucidating novel molecular mechanisms underlying cholesterol and lipid transfer into milk.

Gene networks driving bovine milk fat synthesis during the lactation cycle

Background

The molecular events associated with regulation of milk fat synthesis in the bovine mammary gland remain largely unknown. Our objective was to study mammary tissue mRNA expression via quantitative PCR of 45 genes associated with lipid synthesis (triacylglycerol and phospholipids) and secretion from the late pre-partum/non-lactating period through the end of subsequent lactation. mRNA expression was coupled with milk fatty acid (FA) composition and calculated indexes of FA desaturation and de novo synthesis by the mammary gland.

Results

Marked up-regulation and/or % relative mRNA abundance during lactation were observed for genes associated with mammary FA uptake from blood (LPL, CD36), intracellular FA trafficking (FABP3), long-chain (ACSL1) and short-chain (ACSS2) intracellular FA activation, de novo FA synthesis (ACACA, FASN), desaturation (SCD, FADS1), triacylglycerol synthesis (AGPAT6, GPAM, LPIN1), lipid droplet formation (BTN1A1, XDH), ketone body utilization (BDH1), and transcription regulation (INSIG1, PPARG, PPARGC1A). Change in SREBF1 mRNA expression during lactation, thought to be central for milk fat synthesis regulation, was ≤2-fold in magnitude, while expression of INSIG1, which negatively regulates SREBP activation, was >12-fold and had a parallel pattern of expression to PPARGC1A. Genes involved in phospholipid synthesis had moderate up-regulation in expression and % relative mRNA abundance. The mRNA abundance and up-regulation in expression of ABCG2 during lactation was markedly high, suggesting a biological role of this gene in milk synthesis/secretion. Weak correlations were observed between both milk FA composition and desaturase indexes (i.e., apparent SCD activity) with mRNA expression pattern of genes measured.

Conclusion

A network of genes participates in coordinating milk fat synthesis and secretion. Results challenge the proposal that SREBF1 is central for milk fat synthesis regulation and highlight a pivotal role for a concerted action among PPARG, PPARGC1A, and INSIG1. Expression of SCD, the most abundant gene measured, appears to be key during milk fat synthesis. The lack of correlation between gene expression and calculated desaturase indexes does not support their use to infer mRNA expression or enzyme activity (e.g., SCD). Longitudinal mRNA expression allowed development of transcriptional regulation networks and an updated model of milk fat synthesis regulation.

Identification of the tree shrew ATP-binding cassette transporter A1 (ABCA1) and its expression in tissues : cDNA sequence and expression of tree shrew ABCA1

ATP-binding cassette transporter A1 (ABCA1) modulates plasma levels of high density lipoprotein (HDL), a cardiovascular protecting factor. Tree shrew was considered to be an animal protected from atherosclerosis characterized by high proportion of HDL in plasma. The cDNA clones and expression of tree shrew ABCA1 was identified using SMART-RACE and Real-Time PCR techniques respectively. The nucleotide sequence of tree shrew ABCA1 covered 7,762 bp, including a 6,786 bp coding region which encoded a 2,261 amino acids protein with the high identity to human ABCA1 (95%). Tree shrew ABCA1 was expressed in various tissues, the highest in lung, followed by liver, kidney, spleen and cardiac muscle in turn from high to medium expression levels. This pattern was partially different from that of human ABCA1 which was low in kidney and cardiac muscle. This work could shed new light on its role of ABCA1 in the distinctive HDL metabolism in tree shrew.