Regulation of the human apolipoprotein AIV gene expression in transgenic mice

Changes in serum levels of Apo AIV in patients with newly diagnosed hyperthyroidism and hypothyroidism: a preliminary study

OBJECTIVES

Apolipoprotein AIV has a role in chylomicrons and lipid secretion and catabolism. Also, Apo-AIV plays a role in the regulation of appetite and satiety. Previous studies on rats have shown that hyperthyroidism and hypothyroidism are associated with significant changes in Apo-AIV serum levels. There has been no research on serum Apo-AIV changes in hyper and hypothyroidism in humans.

METHODS

This case-control study was performed on new patients with hyper and hypothyroidism. Eighteen patients with hyperthyroidism and 18 patients with hypothyroidism enrolled in the study. After 12 weeks treatment blood samples were recruited. If euthyroidism was achieved, serum Apo-AIV level was measured. Eighteen euthyroid healthy individuals without thyroid disease were chosen as the control group from general population.

RESULTS

Serum levels of Apo-AIV before treatment in hypothyroidism, hyperthyroidism and in the control group were 85.61, 110.66 and 33.51 mg/dL respectively (p<0.001), which was significantly higher in hyperthyroid patients than hypothyroidism and control group. In patients with hyperthyroidism there was a significant decrease in serum levels of Apo-AIV after treatment (p=0.044). However in hypothyroidism a non-significant elevation in serum levels of Apo-AIV was observed (p=0.403). Furthermore, serum levels of Apo-AIV after treatment were significantly higher in both hyperthyroidism and hypothyroidism in comparison to control group (p<0.001).

CONCLUSIONS

The results of this study for the first time showed that the serum level of Apo-AIV is increased in patients with hyperthyroidism and is decreased in patients with hypothyroidism, and after treatment, there was a significant difference with the control group.

RNA splicing in human disease and in the clinic

Defects at the level of the pre-mRNA splicing process represent a major cause of human disease. Approximately 15-50% of all human disease mutations have been shown to alter functioning of basic and auxiliary splicing elements. These elements are required to ensure proper processing of pre-mRNA splicing molecules, with their disruption leading to misprocessing of the pre-mRNA molecule and disease. The splicing process is a complex process, with much still to be uncovered before we are able to accurately predict whether a reported genomic sequence variant (GV) represents a splicing-associated disease mutation or a harmless polymorphism. Furthermore, even when a mutation is correctly identified as affecting the splicing process, there still remains the difficulty of providing an exact evaluation of the potential impact on disease onset, severity and duration. In this review, we provide a brief overview of splicing diagnostic methodologies, from in silico bioinformatics approaches to wet lab in vitro and in vivo systems to evaluate splicing efficiencies. In particular, we provide an overview of how the latest developments in high-throughput sequencing can be applied to the clinic, and are already changing clinical approaches.

Apolipoprotein A-IV, a putative satiety/antiatherogenic factor, rises after gastric bypass

Roux-en-Y gastric bypass surgery (RYGBP) leads to improvements in satiety and obesity-related comorbidities. The mechanism(s) underlying these improvements are not known but may be revealed in part by discovery proteomics. Therefore, fasting plasma was collected from 12 subjects (mean BMI >45) during RYGBP and during a second procedure approximately 17 months later. Body weight, obesity-related comorbidities, and medication use were decreased after RYGBP. Mass spectrometry-based proteomic analysis was performed on a subset of seven samples using isobaric isotope-coded affinity tags (four plex iTRAQ). Initial proteomic analysis (n = 7) quantified and identified hundreds of plasma proteins. Manual inspection of the data revealed a 2.6 +/- 0.5-fold increase in apolipoprotein A-IV (apo A-IV, gene designation: APOA4), a approximately 46-kDa glycoprotein synthesized mainly in the bypassed small bowel and liver after RYGBP. The change in apo A-IV was significantly greater than other apolipoproteins. Immunoblot analysis of the full longitudinal sample set (n = 12) indicated even higher increases (8.3 +/- 0.2 fold) in apo A-IV. Thus iTRAQ may underestimate the changes in protein concentrations compared to western blotting of apo A-IV. Apo A-IV inhibits gastric emptying and serves as a satiety factor whose synthesis and secretion are increased by the ingestion of dietary fat. It also possesses anti-inflammatory and antiatherogenic properties. Based on these functions, we speculate changes in apo A-IV may contribute to weight loss as well as the improvements in inflammation and cardiovascular disease after RYGBP. In addition, the findings provide evidence validating the use of iTRAQ proteomics in discovery-based studies of post-RYGBP improvements in obesity-related medical comorbidities.

The expression of intact and mutant human apoAI/CIII/AIV/AV gene cluster in transgenic mice

The apoAI/CIII/AIV gene cluster is involved in lipid metabolism and has a complex pattern of gene expression modulated by a common regulatory element, the apoCIII enhancer. A new member of this cluster, apolipoprotein (apo) AV, has recently been discovered as a novel modifier in triglyceride metabolism. To determine the expression of all four apo genes in combination and, most importantly, whether the transcription of apoAV is coregulated by the apoCIII enhancer in the cluster, we generated an intact transgenic line carrying the 116-kb human apoAI/CIII/AIV/AV gene cluster and a mutant transgenic line in which the apoCIII enhancer was deleted from the 116-kb structure. We demonstrated that the apoCIII enhancer regulated hepatic and intestinal apoAI, apoCIII, and apoAIV expression; however, it did not direct the newly identified apoAV in the cluster. Furthermore, human apo genes displayed integrated position-independent expression and a closer approximation of copy number-dependent expression in the intact transgenic mice. Because apoCIII and apoAV play opposite roles in triglyceride homeostasis, we analyzed the lipid profiles in our transgenic mice to assess the effects of human apoAI gene cluster expression on lipid metabolism. The triglyceride level was elevated in intact transgenic mice but decreased in mutant ones compared with nontransgenic mice. In addition, the expression of human apoAI and apoAIV elevated high density lipoprotein cholesterol in transgenic mice fed an atherogenic diet. In conclusion, our studies with human apoAI/CIII/AIV/AV gene cluster transgenic models showed that the apoCIII enhancer regulated expression of apoAI, apo-CIII, and apoAIV but not apoAV in vivo and showed the influences of expression of the entire cluster on lipid metabolism.

Antioxidative and antiatherosclerotic effects of human apolipoprotein A-IV in apolipoprotein E-deficient mice

Mice expressing human apolipoprotein A-IV (apoA-IV) mainly in the intestine were obtained in an apolipoprotein E-deficient (apoE(0)) background (apoA-IV/E(0) mice). Quantification of aortic lesions and plasma lipid determination showed that compared with their control apoE(0) counterparts, the apoA-IV/E(0) mice are protected against atherosclerosis without an increase in HDL cholesterol. Because oxidized lipoproteins play an important role in atherogenesis, we tested whether the protection observed in these animals is accompanied by an in vivo reduction of the oxidation parameters. The lag time in the formation of conjugated dienes during copper-mediated oxidation, the aggregation state of LDL, and the presence of anti-oxidized LDL antibodies were measured. The presence of oxidized proteins in tissues and the presence of oxidation-specific epitopes in heart sections of atherosclerotic lesions were also analyzed. Except for lag time, the results showed that the oxidation parameters were reduced in the apoA-IV/E(0) mice compared with the apoE(0) mice. This suggests that human apoA-IV acts in vivo as an antioxidant. In addition, human apoA-IV accumulation was detected in the atherosclerotic lesions of apoA-IV/E(0) mice, suggesting that apoA-IV may inhibit oxidative damage to local tissues, thus decreasing the progression of atherosclerosis.

Expression of human apolipoprotein A-I/C-III/A-IV gene cluster in mice induces hyperlipidemia but reduces atherogenesis

The apolipoprotein (apo)A-I/C-III/A-IV gene cluster is involved in lipid metabolism and atherosclerosis. Overexpression of apoC-III in mice causes hypertriglyceridemia and induces atherogenesis, whereas overexpression of apoA-I or apoA-IV increases cholesterol in plasma high density lipoprotein (HDL) and protects against atherosclerosis. Each gene has been studied alone in transgenic mice but not in combination as the entire cluster. To determine which phenotype is produced by the expression of the entire gene cluster, transgenic mice were generated with a 33-kb human DNA fragment. The results showed that the transgene contained the necessary elements to direct hepatic and intestinal expression of the 3 genes. In the pooled data, plasma concentrations were 257+/-9, 7.1+/-0.5, and 1.0+/-0.2 mg/dL for human apoA-I, apoC-III, and apoA-IV, respectively (mean+/-SEM). Concentrations of these apolipoproteins were higher in males than in females. Human apoA-I and apoC-III concentrations were positively correlated, suggesting that they are coregulated. Transgenic mice exhibited gross hypertriglyceridemia and accumulation of apoB(48)-containing triglyceride-rich lipoproteins. Plasma triglyceride and cholesterol concentrations were correlated positively with human apoC-III concentration, and HDL cholesterol was correlated with apoA-I concentration. In an apoE-deficient background, despite being markedly hypertriglyceridemic, cluster transgenic animals compared with nontransgenic animals showed a 61% reduction in atherosclerosis. This suggests that apoA-I and/or apoA-IV can protect against atherosclerosis even in the presence of severe hyperlipidemia. These mice provide a new model for studies of the regulation of the 3 human genes in combination.

Human apolipoprotein A-IV reduces gastric acid secretion and diminishes ulcer formation in transgenic mice

We have investigated the involvement of human apolipoprotein A-IV (apoA-IV) in gastric acid secretion and ulcer formation in recently generated apoA-IV transgenic mice. Compared to control littermates, transgenic animals showed a gastric acid secretion decreased by 43-77% whereas only slight variations were observed in the different cell population densities within the gastric mucosa. In addition, no variation in gastrin levels was observed. Transgenics were protected against indomethacin-induced ulcer formation, with lesions diminishing by 45 to 64% compared to controls. These results indicate that endogenous apoA-IV expression can regulate gastric acid secretion and ulcer development.