NCBI Summary:
This gene product is the main apolipoprotein of chylomicrons and low density lipoproteins. It occurs in plasma as two main isoforms, apoB-48 and apoB-100: the former is synthesized exclusively in the gut and the latter in the liver. The intestinal and the hepatic forms of apoB are encoded by a single gene from a single, very long mRNA. The two isoforms share a common N-terminal sequence. The shorter apoB-48 protein is produced after RNA editing of the apoB-100 transcript at residue 2180 (CAA->UAA), resulting in the creation of a stop codon, and early translation termination. Mutations in this gene or its regulatory region cause hypobetalipoproteinemia, normotriglyceridemic hypobetalipoproteinemia, and hypercholesterolemia due to ligand-defective apoB, diseases affecting plasma cholesterol and apoB levels. [provided by RefSeq, Jul 2008]
General function
Ligand
Comment
Cellular localization
Secreted
Comment
Apolipoprotein A-I and B levels, dyslipidemia and metabolic syndrome in south-west Chinese women with PCOS. Zhang J et al. (2012) What are the relationships between apolipoprotein (apo) A-I and apoB concentrations, the apoB/apoA-I ratio and the prevalences of dyslipidemia and metabolic syndrome (MS) in south-west Chinese women with polycystic ovary syndrome (PCOS). There is a relatively high incidence of dyslipidemia and MS in south-west Chinese women with PCOS, especially in patients without hyperandrogenism. Patients with dyslipidemia are more obese, and have a more adverse glucose and lipid metabolic profile and higher apoB levels and apoB/apoA-I ratio. The increased apoB levels and apoB/A1 ratio and the MS are strongly associated with PCOS, suggesting that there is an increased risk of cardiovascular diseases in these patients. Dyslipidemia and MS have been widely studied in women with PCOS, but to date no data from south-west Chinese subjects have been available. The apoB/apoA-I ratio has been reported to be strongly associated with MS and insulin resistance (IR) and to be a reliable parameter that reflects lipid disturbances and the potential to develop atherosclerosis, but its relationship with PCOS is unclear. DESIGN This case-control study included 406 patients with PCOS and 342 control women between 17 and 40 years of age from a population in south-west China during 2006-2011. The diagnosis of PCOS was based on the revised 2003 Rotterdam criteria. The control group, consisting of women with infertility due to a Fallopian obstruction or the husband's infertility, women undergoing a pre-pregnancy check and healthy volunteers, was recruited from the same hospital during the same period. All women were not taking any medication known to affect carbohydrate or lipid or hormone metabolism for at least 3 months prior to the study, and were studied during the follicular phase of their menstrual cycle. MS was assessed by the National Cholesterol Education Program-Adult treatment Panel (NCEP-ATP) III criteria modified for Asian populations. Dyslipidemia was defined by one or more of the following conditions: fasting total cholesterol≥5.7 mmol/l, fasting triglycerides (TG)≥1.7 mmol/l, fasting high-density lipoprotein cholesterol (HDL-C)<1.29 mmol/l or fasting low-density lipoprotein cholesterol (LDL-C)≥3.6 mmol/l. The prevalence of dyslipidemia in patients with PCOS was 52.96%, about two times than that in the controls, 28.95%. The most common components of dyslipidemia in patients with PCOS were decreased HDL-C (41.13%) and increased TG (24.14%). PCOS patients with dyslipidemia had significantly higher TG/HDL-C ratios, and lower HDL-C and apoA-I levels when compared with the controls or patients without dyslipidemia, and had significantly higher BMIs, fasting insulin concentrations, 2-h insulin and glucose levels, homeostatic model assessment IR, TG levels, LDL-C levels, atherogenic indexes, apoB concentrations and apoB/apoA-I ratios when compared with all of the control women, with or without dyslipidemia and patients without dyslipidemia. The frequency of MS in patients with PCOS was 25.62%, more than five times than that in the controls. The main two risk factors were increased waist circumference and low HDL-C levels. In the four PCOS phenotypes based on the Rotterdam criteria, the oligo- and/or anovulation+PCO presented the highest prevalence of dyslipidemia (66.14%) and MS (34.65%). Binary logistic regression analysis showed that increased apoB levels, an increased apoB/apoA-I ratio and MS was strongly associated with PCOS (odds ratio=17.41, 27.16 and 7.66, 95% confidence interval: 6.93-43.74, 9.46-77.93 and 4.32-13.57, respectively) after adjustment for age. The relatively minor limitations of this study are discussed within the paper. GENERALISABILITY TO OTHER POPULATIONS: The metabolic patterns found in south-west Chinese with PCOS are compared with that of other populations. This work was supported by Chinese National Natural Science Foundation (81070463), Program for Changjiang Scholars and Innovative Research Team in University (IRT0935), and Research Seed Fund from West China Second Hospital of Sichuan University (to H.B.). There are no any competing interests. N/A.//////////////////
Ovarian function
Steroid metabolism
Comment
Human luteinized granulosa cells secrete apoB100-containing lipoproteins. Gautier T et al. Thus far, liver, intestine, heart and placenta have been shown to secrete apolipoprotein(apo)B-containing lipoproteins. In the present study we first investigated lipoproteins in human follicular fluid (FF), surrounding developing oocytes within the ovary, as well as in corresponding plasma samples (n=12). HDL cholesterol (HDL-C) within FF correlated well with plasma HDL-C (r=0.80, p<0.01), while VLDL-C did not, indicating that VLDL in FF might originate directly from the granulosa cells producing FF. Primary human granulosa cells expressed apoB, microsomal triglyceride transfer protein and apoE, however, not the apoB-editing enzyme apobec-1. Using 3H-leucine we show that granulosa cells secrete apoB100-containing lipoproteins and that secretion can be stimulated by adding oleate to the medium (+83%). With electron microscopy apoB-containing lipoproteins within the secretory pathway of human granulosa cells were directly visualized. Finally, we found a positive relationship between apoB levels in follicular fluid and improved fertility parameters in a population of 27 women undergoing in vitro fertilization. This study demonstrates that human granulosa cells assemble and secrete apoB100-containing lipoproteins, thereby identifying a novel cell type equipped with these properties. These results might have important implications for female infertility phenotypes as well as for the development of drugs targeting the VLDL production pathway.
Expression regulated by
FSH, LH
Comment
Apolipoprotein B is regulated by gonadotropins and constitutes a predictive biomarker of IVF outcomes. Scalici E et al. (2016) Follicular fluid (FF) is an important micro-environment influencing oocyte growth, its development competence, and embryo viability. The FF content analysis allows to identify new relevant biomarkers, which could be predictive of in vitro fertilization (IVF) outcomes. Inside ovarian follicle, the amount of FF components from granulosa cells (GC) secretion, could be regulated by gonadotropins, which play a major role in follicle development. This prospective study included 61 female undergoing IVF or Intra-cytoplasmic sperm injection (ICSI) procedure. Apolipoprotein B (APOB) concentrations in follicular fluid and APOB gene and protein expression in granulosa cells from reproductively aged women undergoing an in vitro fertilization program were measured. The statistical analyses were performed according to a quartile model based on the amount of APOB level found in FF. Amounts of APOB were detected in human FF samples (mean ± SD: 244.6 ± 185.9 ng/ml). The odds of obtaining an oocyte in the follicle and a fertilized oocyte increased significantly when APOB level in FF was higher than 112 ng/ml [i.e., including in Quartile Q 2, Q3 and Q4] (p = 0.001; p < 0.001, respectively). The probabilities of obtaining an embryo and a top quality embryo on day 2, were significantly higher if APOB levels were within the ranges of 112 and 330 ng/ml (i.e. in Q2 and Q3) or 112 and 230 ng/ml (i.e. in Q2), respectively (p < 0.001; p = 0.047, respectively). In addition, our experiments in vitro indicated that APOB gene and protein expression, along with APOB content into culture were significantly under-expressed in GC upon stimulation with gonadotropins (follicular stimulating hormone: FSH and/or human chorionic gonadotropin: hCG). We are reporting a positive and statistically significant associations between APOB and oocyte retrieval, oocyte fertilization, and embryo quality. Using an experimental study component, the authors report significant reduced APOB expression and content for luteinized granulosa cells cultured in the presence of gonadotropins.//////////////////