apoM mRNA Levels Research Articles

Mechanism of liver X receptor α and ATP binding cassette transporter A1 involved in preeclampsia using an optimized deep learning model.

Preeclampsia (PE) is a complex disease-causing multisystem damage. Many genes, environmental factors, and their interactions are involved in the development and progression of PE. The pathogenesis of PE is not fully understood, limiting the prevention and treatment of PE. The aim of this study was to investigate the effect of 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS), an ATP-binding cassette transporter A1 (ABCA1) blocker, on apoM mRNA and protein levels. The role of liver X receptor α (LXRα) and ABCA1 in the pathogenesis of PE was investigated by optimizing the design of DIDS inhibition based on a deep learning model. The proportion of primipara in the research group, EOPE group, LOPE group, and controls was 59.82%, 65.85%, 56.34%, and 21.43%, respectively. The difference between the research group and the controls was statistically significant (p<0.01). In the clinical data, serum-free triiodothyronine (FT3), gestational age at delivery, high-density lipoprotein cholesterol (HDL-C), hemoglobin (HGB), albumin, and platelet (PLT) in the research group were lower than those in the controls (p<0.05). ABCA1 is considered to affect apoM mRNA expression, G/HDL-C may increase the risk of LOPE, and overweight or obesity, abnormal glycemic regulation, and hypothyroidism are independent risk factors closely related to the pathogenesis of PE and its subgroups.

Isoform-Dependent Effects of Apolipoprotein E on Sphingolipid Metabolism in Neural Cells.

Sphingosine 1-phosphate (S1P) and ceramides have been implicated in the development of Alzheimer's disease. Apolipoprotein E (ApoE) isoforms are also involved in the development of Alzheimer's disease. We aimed at elucidating the potential association of the ApoE isoforms with sphingolipid metabolism in the central nervous system. We investigated the modulations of apolipoprotein M (apoM), a carrier of S1P, S1P, and ceramides in Apoeshl mice, which spontaneously lack apoE, and U251 cells and SH-SY5Y cells infected with adenovirus vectors encoding for apoE2, apoE3, and apoE4. In the brains of Apoeshl mice, the levels of apoM were lower, while those of ceramides were higher. In U251 cells, cellular apoM and S1P levels were the highest in the cells overexpressing apoE2 among the apoE isoforms. The cellular and medium contents of ceramides decreased in the order of the cells overexpressing apoE3 > apoE2 and increased in the cells overexpressing apoE4. In SH-SY5Y cells, apoM mRNA and medium S1P levels were also the highest in the cells overexpressing apoE2. The cellular contents of ceramides decreased in the order of the cells overexpressing apoE3 > apoE2 = apoE4 and those in medium decreased in the order of the cells overexpressing apoE3 > apoE2, while increased in the cells overexpressing apoE4. The modulation of apoM and S1P might partly explain the protective effects of apoE2 against Alzheimer's disease, and the modulation of ceramides might be one of the mechanisms explaining the association of apoE4 with the development of Alzheimer's disease.

Berberine reduces gut-vascular barrier permeability via modulation of ApoM/S1P pathway in a model of polymicrobial sepsis

AimsThe hyperpermeability of gut-vascular barrier (GVB) plays a role in gut-derived sepsis. The goal of this study was to evaluate if berberine might improve hepatic apolipoprotein M (ApoM) generation and raise plasma ApoM level to protect the compromised GVB. Materials and methodsThe compromised GVB was induced by sepsis. Hepatic ApoM mRNA and phosphoenolpyruvate carboxykinase (PEPCK) mRNA and plasma ApoM level were assayed by qRT-PCR and ELISA, respectively. The permeability of intestinal capillary in vivo and of rat intestinal microvascular endothelial cells (RIMECs) in vitro was assayed by FITC-dextran. The blood glucose was detected by a glucometer. Plasma insulin, TNF-α and IL-1β were assayed by ELISA. The plasmalemma vesicle-associated protein-1 (PV1), β-catenin and occludin in RIMECs were assayed by Western blot. Key findingsSepsis decreased hepatic ApoM mRNA and plasma ApoM level, but raised hepatic PEPCK mRNA and plasma glucose, insulin, TNF-α, and IL-1β levels. The increased vascular endothelial permeability was abrogated by recombinant rat ApoM in vivo or ApoM-bound S1P in vitro. ApoM-bound S1P decreased PV1 but increased occludin and β-catenin expression in LPS-treated RIMECs. Berberine in a dose-dependent manner raised hepatic ApoM mRNA and plasma ApoM level, but decreased septic hyperglycemia, insulin resistance and plasma TNF-α and IL-1β levels. Berberine reduced sepsis-induced PEPCK and TLR4 mRNA overexpression in the liver. SignificanceThis study demonstrated berberine inhibited TLR4-mediated hyperglycemia, insulin resistance and proinflammatory molecule production, thereby increasing ApoM gene expression and plasma ApoM. Berberine protected the damaged GVB via modulation of ApoM/S1P pathway.

Apolipoprotein M: a novel adipokine decreasing with obesity and upregulated by calorie restriction

The adipose tissue (AT) is a secretory organ producing a wide variety of factors that participate in the genesis of metabolic disorders linked to excess fat mass. Weight loss improves obesity-related disorders. Transcriptomic studies on human AT, and a combination of analyses of transcriptome and proteome profiling of conditioned media from adipocytes and stromal cells isolated from human AT, have led to the identification of apolipoprotein M (apoM) as a putative adipokine. We aimed to validate apoM as novel adipokine, investigate the relation of AT APOM expression with metabolic syndrome and insulin sensitivity, and study the regulation of its expression in AT and secretion during calorie restriction-induced weight loss. We examined APOM mRNA level and secretion in AT from 485 individuals enrolled in 5 independent clinical trials, and in vitro in human multipotentadipose-derived stem cell adipocytes. APOM expression and secretion were measured during dieting. APOM was expressed in human subcutaneous and visceral AT, mainly by adipocytes. ApoM was released into circulation from AT, and plasma apoM concentrations correlate with AT APOM mRNA levels. In AT, APOM expression inversely correlated with adipocyte size, was lower in obese compared to lean individuals, and reduced in subjects with metabolic syndrome and type 2 diabetes. Regardless of fat depot, there was a positive relation between AT APOM expression and systemic insulin sensitivity, independently of fat mass and plasma HDL cholesterol. In human multipotentadipose-derived stem cell adipocytes, APOM expression was enhanced by insulin-sensitizing peroxisome proliferator-activated receptor agonists and inhibited by tumor necrosis factor α, a cytokine that causes insulin resistance. In obese individuals, calorie restriction increased AT APOM expression and secretion. ApoM is a novel adipokine, the expression of which is a hallmark of healthy AT and is upregulated by calorie restriction. AT apoM deserves further investigation as a potential biomarker of risk for diabetes and cardiovascular diseases.

Increased apolipoprotein M induced by lack of scavenger receptor BI is not activated via HDL-mediated cholesterol uptake in hepatocytes

BackgroundScavenger receptor BI (SR-BI) is a classic high-density lipoprotein (HDL) receptor, which mediates selective lipid uptake from HDL cholesterol esters (HDL-C). Apolipoprotein M (ApoM), as a component of HDL particles, could influence preβ-HDL formation and cholesterol efflux. The aim of this study was to determine whether SR-BI deficiency influenced the expression of ApoM.MethodsBlood samples and liver tissues were collected from SR-BI gene knockout mice, and serum lipid parameters, including total cholesterol (TC), triglyceride (TG), high and low-density lipoprotein cholesterol (HDL-C and LDL-C) and ApoM were measured. Hepatic ApoM and ApoAI mRNA levels were also determined. In addition, BLT-1, an inhibitor of SR-BI, was added to HepG2 cells cultured with cholesterol and HDL, under serum or serum-free conditions. The mRNA and protein expression levels of ApoM were detected by RT-PCR and western blot.ResultsWe found that increased serum ApoM protein levels corresponded with high hepatic ApoM mRNA levels in both male and female SR-BI−/− mice. Besides, serum TC and HDL-C were also significantly increased. Treatment of HepG2 hepatoma cells with SR-BI specific inhibitor, BLT-1, could up-regulate ApoM expression in serum-containing medium but not in serum-free medium, even in the presence of HDL-C and cholesterol.ConclusionsResults suggested that SR-BI deficiency promoted ApoM expression, but the increased ApoM might be independent from HDL-mediated cholesterol uptake in hepatocytes.

Increased mRNA levels of apolipoprotein M and apolipoprotein AI in the placental tissues with fetal macrosomia.

The present study examined mRNA levels of apolipoprotein M (apoM) and apolipoprotein AI (apoAI) in the term placental tissues obtained from 37 women with normal birth weight neonates and from 37 women with macrosomic neonates (birth body weight ≥4,000 g), and further discussed possible clinical significance of these observations. The mRNA levels of apoM and apoAI in the placental tissues were determined by the real time RT-PCR, which demonstrated that both apoM and apoAI mRNA levels were significantly higher in the placentas from macrosomia than those from normal birth. Moreover, we analyzed the overexpressions of apoM and apoAI with the clinical data. Meanwhile we examined several known risk factors of macrosomia including the mRNA levels of insulin-like growth factor I (IGF-I), IGF-II, insulin-like growth factor I receptor (IGF-IR) and IGF-IIR. It demonstrated that apoM expression was significantly positively correlated to the placental weight, fetal birth weight, pregestational body mass index (BMI), weight gain during pregnancy, maternal weight, maternal BMI and the mRNA levels of IGF-IR as well as IGF-IIR. The apoAI mRNA level was statistically significantly correlated to the placental weight, fetal birth weight, IGF-I and IGF-IR mRNA levels. Binary logistic regression analysis suggested that both apoM and apoAI mRNA may considered as independent risk factors for macrosomia. The clinical significance needs further investigation.

Dihydrotestosterone regulating apolipoprotein M expression mediates via protein kinase C in HepG2 cells

BackgroundAdministration of androgens decreases plasma concentrations of high-density lipid cholesterol (HDL-C). However, the mechanisms by which androgens mediate lipid metabolism remain unknown. This present study used HepG2 cell cultures and ovariectomized C57BL/6 J mice to determine whether apolipoprotein M (ApoM), a constituent of HDL, was affected by dihydrotestosterone (DHT).MethodsHepG2 cells were cultured in the presence of either DHT, agonist of protein kinase C (PKC), phorbol-12-myristate-13-acetate (PMA), blocker of androgen receptor flutamide together with different concentrations of DHT, or DHT together with staurosporine at different concentrations for 24 hrs. Ovariectomized C57BL/6 J mice were treated with DHT or vehicle for 7d or 14d and the levels of plasma ApoM and livers ApoM mRNA were measured. The mRNA levels of ApoM, ApoAI were determined by real-time RT-PCR. ApoM and ApoAI were determined by western blotting analysis.ResultsAddition of DHT to cell culture medium selectively down-regulated ApoM mRNA expression and ApoM secretion in a dose-dependent manner. At 10 nM DHT, the ApoM mRNA levels were about 20% lower than in untreated cells and about 40% lower at 1000 nM DHT than in the control cells. The secretion of ApoM into the medium was reduced to a similar extent. The inhibitory effect of DHT on ApoM secretion was not blocked by the classical androgen receptor blocker flutamide but by an antagonist of PKC, Staurosporine. Agonist of PKC, PMA, also reduced ApoM. At 0.5 μM PMA, the ApoM mRNA levels and the secretion of ApoM into the medium were about 30% lower than in the control cells. The mRNA expression levels and secretion of another HDL-associated apolipoprotein AI (ApoAI) were not affected by DHT. The levels of plasma ApoM and liver ApoM mRNA of DHT-treated C57BL/6 J mice were lower than those of vehicle-treated mice.ConclusionsDHT directly and selectively down-regulated the level of ApoM mRNA and the secretion of ApoM by protein kinase C but independently of the classical androgen receptor.

Apolipoprotein M expression in human colorectal cancer tissues and its clinicopathological relevance

To investigate the mRNA and protein expression levels of apolipoprotein M (apoM) in the human colorectal cancer tissues, and to explore its clinical relevance. Real-time PCR was carried out to determine the mRNA expression levels both in cancer tissue and its adjacent normal tissue from 20 patients with colorectal cancer. Immunohistochemistry was also carried out to determine the protein levels in 23 colorectal biopsy samples (7 normal mucosa, 6 inflammatory mucosa and 10 polyp tissues) and 20 cases of colorectal cancer tissues as well as the adjacent normal tissues. Real-time PCR result showed that apoM mRNA level in the colorectal cancer tissues was significantly lower than that in their adjacent normal tissues (0.05±0.01 vs. 0.19±0.05, P<0.05). ApoM mRNA level in colorectal cancer tissues was statistically significant higher in the patients with lymph node metastasis as compared to the patients without lymph node metastasis (P<0.01). The median value of apoM protein in cancer tissues was 5.50, which was significantly lower than that in the adjacent normal tissues (10.5, P<0.05), inflammatory mucosa tissues (9.75, P<0.05), polyp tissues (11.0, P<0.01) and normal mucosa (10.5, P<0.05). No significant association was observed between the apoM protein level and the clinicopathological parameters of patients. Both apoM mRNA and protein expression levels in colorectal cancer tissues are significantly decreased in contrast to normal and benign colorectal tissues. The apoM mRNA expression in colorectal cancer tissues is closely associated with nodal metastasis.

ABCA1 upregulating apolipoproein M expression mediates via the RXR/LXR pathway in HepG2 cells

We have previously reported that liver X receptor (LXR) agonist, TO901317, could significantly inhibit hepatic apolipoprotein M (apoM) expression. It has been reported that TO901317 could activate the ATP-binding cassette transporter A1 (ABCA1) that mediates cholesterol efflux to the lipid-poor apoAI, which is an essential step for the high-density lipoprotein (HDL) formation. It is unknown if ABCA1 may regulate hepatic apoM expression. In the present study, HepG2 cells were cultured with the synthetic LXR agonists, TO901317 or GW3965 in the presence or absence of ABCA1 antagonist, disodium 4,4′-diisothiocyanatostilbene- 2,2′-disulfonate (DIDS). The mRNA levels of ABCA1, apoM and liver receptor homolog-1 (LRH-1) determined by the real-time RT-PCR. It demonstrated that both TO901317 and GW3965 could significantly enhance ABCA1 expression, and simultaneously, inhibit LRH1 expression. However, TO901317 alone could significantly inhibit apoM expression, while GW3965 alone did not influence apoM expression. ABCA1 antagonist, DIDS, have no effects on GW3965 induced upregulation of ABCA1 and downregulation of LRH1. However, apoM mRNA level was significantly decreased when the cells cultured with GW3965 together with DIDS. The present study demonstrated that apoM expression could be elevated by ABCA1 via the RXR/LXR pathway and LRH1 does not involve in the regulation of apoM by the activation of ABCA1, although the direct regulative pathway(s) between ABCA1 and apoM gene is still unknown yet. The detailed mechanism needs further investigation.

Effects of simvastatin on apolipoprotein M in vivo and in vitro

ObjectiveTo investigate effects of lipid lowering drug, simvastatin, on apolipoprotein M expression in the hyperlipidemic mice and in hepatic cell line, HepG2 cells.MethodsSwiss male mice were randomly divided into the high fat group and control group, and were intragastrically fed with 0.9% saline (control group) or lipid emulsion (high fat group) at the daily dosage of 15 ml/kg body weight, respectively. After 8 weeks feeding, the hyperlipidemic model was successfully induced and these hyperlipidemic mice were then randomly divided into three experimental groups: vehicle control group, high-dose simvastatin-treated group (100 mg/kg body weight), and low-dose simvastatin-treated group (10 mg/kg body weight). Mice were dosed daily for 6 weeks of simvastatin before mice were sacrificed for determining serum lipid profile and apoM protein levels that was determined by using dot blotting analysis. Effects of simvastatin on apoM mRNA expression in the HepG2 cells were determined by real-time RT-PCR.ResultsComparing to high fat model mice without simvastatin treatment, 100 mg/kg simvastatin could significantly increase serum total cholesterol (P < 0.05). Serum apoM levels, in all mice, were significantly lower in the mice at the age of 26 weeks than the mice at 12 weeks old (P < 0.05), which indicated that serum apoM levels were significantly correlated to the mice age. It demonstrated also that treatment of simvastatin did not influence serum apoM levels in these mouse model, although serum apoM levels were increased by about 13% in the 10 mg/kg simvastatin group than in the vehicle control group without simvastatin. In HepG2 cell cultures, simvastatin could significantly decrease apoM mRNA levels with dose- and time-dependent manners. At 10 μM simvastatin treatment, apoM mRNA decreased by 52% compared to the controls.ConclusionThe present study suggested that simvastatin, in vivo, had no effect on apoM levels in the hyperlipidemic mouse model. ApoM serum levels in mice were significantly correlated to the animal's age, whereas in cell cultures simvastatin does inhibit apoM expression in the HepG2 cells. The mechanism behind it is not known yet.

Effects of simvastatin on apolipoprotein M in vivo and in vitro

Objective To investigate the effects of simvastatin on apolipoprotein M (apoM) in vivo and in vitro.Methods The 12-weeks-old Kunming male mice ( clean animal) were randomly divided into two groups,and given intragastric administration with 0.9% saline ( control),lipid emulsion ( high fat) at the daily dose of 15 ml/kg respectively.After 8 weeks the hyperlipidemic models were successfully induced and randomly divided into three groups:high fat model control group,high-dose simvastatin-treated group,and regular simvastatin-treated group.Mice were dosed daily for 6 weeks with simvastatin ( 10 or 100 mg/kg body weight) at 20 weeks of age.Mice were sacrificed for examination of serum lipids and the protein levels of apoM in mice serum were estimated by dot blotting analysis.In vitro,apeM mRNA expression in HepG2 cells treated with simvastatin was determined by real-time reverse transcription-polymerase chain reaction (RT-PCR).Results As compared with high fat model control group,100 mg/kg simvastatin significantly increased serum total cholesterol ( P＜0.05 ).At the age of 26 weeks,the serum apoM levels were significantly decreased ( P＜0.05 ) in normal control group,high fat model control group,regular simvastatin-treated group,and high-dose simvastatin-treated group as compared with those at the age of 12 weeks.However,at the age of 26 weeks vs 20 weeks only in normal control group the serum apoM levels were decreased by 17.20% (P＜0.05 ),and the remaining were modestly reduced but had no statistically significant difference (P ＞0.05).Neither 10 mg/kg nor 100 mg/kg simvastatin had effect on serum apoM levels as compared with high fat model control group (P ＞0.05).In vitro,apoM mRNA levels in 10 μmol/L simvastatin-treated group was reduced by 51.93% as compared with control group in HepG2 cells (P＜0.01 ).Conclusion APoM levels were decreased with the increase of age in normal mice.It was likely that age may therefore be of importance for regulation of apoM in Kunming mice. Key words: Simvastatin; Hyperlipidemia; Apolipoprotein

Expression and localization of apolipoprotein M in human colorectal tissues

BackgroundIt has been well documented that apolipoprotein M (apoM) is principally expressed in the liver and kidney. However we found that there was weak apoM expression in other tissues or organs too, which could not be ignored. In the present study, we therefore examined apoM expression in human colorectal tissues including cancer tissues, cancer adjacent normal tissues, polyp tissues and normal mucosa as well as inflammatory mucosa.MethodsTissue samples were collected from patients who underwent surgical resection or endoscopic examination. ApoM mRNA levels were determined by the real-time RT-PCR and apoM protein mass were examined by the immunohistochemistry.ResultsApoM protein can be detected in all colorectal tissues. However, apoM protein mass were significantly lower in the cancer tissues than its matched adjacent normal tissues, polyp tissues, normal mucosa and inflammatory mucosa. In parallel, apoM mRNA levels in the colorectal cancer tissues (0.0536 ± 0.0131) were also significantly lower than those in their adjacent normal tissues (0.1907 ± 0.0563) (P = 0.033). Interestingly, apoM mRNA levels in colorectal cancer tissues were statistic significant higher in the patients with lymph node metastasis than the patients without lymph node metastasis (P = 0.008). Patients under Dukes' C and D stages had much higher apoM mRNA levels than patients under Dukes' A and B stages (P = 0.034).ConclusionIt is concluded that apoM could also be expressed in human colorectal tissues besides liver and kidney. ApoM mRNA levels in the colorectal cancer tissues were significantly increased in the patients with lymph node metastasis. Whether increased apoM expression in the patients with lymph node metastasis being related to patients' prognosis and the physiopathological importance of apoM expression in colorectal tissues need further investigation.

Expression of apolipoprotein M in human hepatocellular carcinoma tissues

The present study examined mRNA levels and protein mass of apolipoprotein M (apoM) in human hepatocellular carcinoma (HCC) tissues and in the adjacent tissues. Plasma apoM levels in these HCC patients were also determined and compared to the normal subjects. The mean level of plasma apoM in the HCC patients was 0.61±0.30 OD mm −2, which was significantly higher than that in the normal subjects 0.37±0.07 OD mm −2 ( P<0.01). However, both apoM mRNA levels and apoM protein mass in the HCC tissues were significantly lower than in the adjacent tissues ( P<0.05). It is concluded that human hepatocellular carcinoma tissues had a reduced capacity to produce apoM than the adjacent non-tumor tissues. However, the plasma apoM levels were higher in the HCC patients than in normal subjects, which suggested that tissues adjacent to the tumors or extra-hepatic apoM production in the HCC patients may contribute to the higher plasma apoM levels in these patients. The clinical significance of apoM in relation to HCC still needs further investigation.

Expressions of apolipoprotein M in hepatocellular carcinoma tissues

Objective To analyze plasma apolipoprotein M (ApoM) level and hepatic apoM mR-NA level in the hepatocellular carcinoma (HCC) patients.Methods Plasma apoM levels were measured by the dot-blot analyses in 36 HCC patients, and 64 normal subjects as control.APOM mRNA levels were detected in the HCC tissues and paracancerous normal liver tissues by RT-PCR, and further conformed by an immunohistochemistry staining method.Results The relative levels of plasma apoM in HCC patients were (0.61 ± 0.30) ODu·mm-2, which were significantly higher than those in the normal subjects [(0.37 ± 0.07) ODu · mm-2] (p < 0.01).apoM mRNA levels in HCC tissues were significantly lower than those in the paracanerous normal tissues (P < 0.05), which was further confirmed by the immunohistochemistry staining.APOM positive staining in HCC tissues was significantly weaker than that in the cancerous normal tissues.Conclusion In HCC patients, apoM mRNA levels in tumor tissues were significantly lower more than those in the paracancerous normal tissues, and plasma apoM levels were significantly higher than those in normal subjects. Key words: Carcinoma,hepatocellular; Apolipoprotein; Immunohistoehemistry

The Signal Peptide Anchors Apolipoprotein M in Plasma Lipoproteins and Prevents Rapid Clearance of Apolipoprotein M from Plasma

Lipoproteins consist of lipids solubilized by apolipoproteins. The lipid-binding structural motifs of apolipoproteins include amphipathic alpha-helixes and beta-sheets. Plasma apolipoprotein (apo) M lacks an external amphipathic motif but, nevertheless, is exclusively associated with lipoproteins (mainly high density lipoprotein). Uniquely, however, apoM is secreted to plasma without cleavage of its hydrophobic NH(2)-terminal signal peptide. To test whether the signal peptide serves as a lipoprotein anchor for apoM in plasma, we generated mice expressing a mutated apoM(Q22A) cDNA in the liver (apoM(Q22A)-Tg mice (transgenic mice)) and compared them with mice expressing wild-type human apoM (apoM-Tg mice). The substitution of the amino acid glutamine 22 with alanine in apoM(Q22A) results in secretion of human apoM without a signal peptide. The human apoM mRNA level in liver and the amount of human apoM protein secretion from hepatocytes were similar in apoM-Tg and apoM(Q22A)-Tg mice. Nevertheless, human apoM was not detectable in plasma of apoM(Q22A)-Tg mice, whereas it was easily measured in the apoM-Tg mice. To examine the plasma metabolism, recombinant apoM lacking the signal peptide was produced in Escherichia coli and injected into wild-type mice. The apoM without signal peptide did not associate with lipoproteins and was rapidly cleared in the kidney. Accordingly, ligation of the kidney arteries in apoM(Q22A)-Tg mice resulted in rapid accumulation of human apoM in plasma. The data suggest that hydrophobic signal peptide sequences, if preserved upon secretion, can anchor plasma proteins in lipoproteins. In the case of apoM, this mechanism prevents rapid loss by filtration in the kidney.

Liver X receptor agonist downregulates hepatic apoM expression in vivo and in vitro

It has been demonstrated that apolipoprotein M (apoM), a recently discovered HDL apolipoprotein, has antiatherosclerotic properties, which may be mediated by the enhancement of reversed cholesterol transportation and/or hepatic cholesterol catabolism. The detailed mechanisms are unknown yet. Liver X receptor (LXR) belongs to the nuclear receptor superfamily and is a ligand-activated transcription factor involved in the regulation of lipid metabolism and inflammation. Activation of LXR in the cell cultures results in an enhancement of cholesterol efflux to apoAI. In the present study, we investigated effects of the LXR agonist, T0901317 on hepatic apoM expression in vivo and in vitro. Serum apoM levels in mice given T0901317 at 10 mg or 100 mg/kg for 7 days were reduced by 12–17% ( P < 0.05). In HepG2 cell cultures, apoM mRNA levels were significantly lower in presence of 25 μM T0901317 (37.1%) than in control cells ( P < 0.001). A similar reduction was found by the addition of 9- cis retinoic acid (RA). Twenty-five micromolar T0901317 together with 100 nM RA decreased apoM mRNA expression by 65% ( P < 0.001). Thus, the LXR agonist T0901317 significantly downregulates apoM mRNA expression in vivo and in vitro, which indicates that apoM is another novel target gene regulated by the LXR. The combination of RA and T0901317 showed additive effects, which suggests that apoM expression can be modulated by LXR/RXR pathway.

Hyperglycemia down-regulates apolipoprotein M expression in vivo and in vitro

Diabetes is associated with low concentrations of apoM in plasma. In db/db mice, ob/ob mice as well as in the alloxan-induced diabetic mouse, the low apoM levels are paralleled by decreased expression of the apoM gene. In the latter model, insulin substitution tended to reverse the low apoM expression. It is not known whether the impairment in apoM expression can be ascribed to hyperglycemia, insulin deficiency or insulin resistance. In the present study, we investigated apoM levels and expression in rats rendered hyperglycemic by short-term glucose infusion. As expected, serum insulin concentrations rose moderately during the infusions. Serum apoM concentrations and hepatic apoM mRNA levels were significantly reduced in the hyperglycemic rats, indicating that the low expression of apoM in these diabetic models can be ascribed to hyperglycemia rather than to insulin deficiency or insulin resistance. However, in HepG2 cells both glucose and insulin markedly inhibited apoM expression these effects were additive. Thus, the possible effects of insulin in vivo seem to be mediated indirectly.

Effects of Ischemia-Reperfusion Injury on Apolipoprotein M Expression in the Liver

The present study investigated the expression pattern of apolipoprotein M (apoM) mRNA in a rat model of hepatic ischemia-reperfusion injury (IRI). Animals were ischemic for 1 hour followed by various reperfusion times. As expected, serum alanine aminotransferase levels were significantly increased under IRI, which indicated the severity of liver injury. Hepatic mRNA levels of HSP70, which is the most common characterized protein within the family of heat-shock proteins (HSP), were significantly increased after 0.5 to 3 hours of IRI. Plasma C-reactive protein, high-density lipoprotein-cholesterol, and lipoprotein (a) levels were significantly increased after 1-hour ischemia followed by 0.5 to 3 hours of reperfusion. Interestingly, similar to HSP70, apoM mRNA levels in the liver were gradually increased after 0.5 to 3 hours of IRI, whereas it returned to a lower level after 6 or 24 hours of IRI, which indicated that hepatic apoM expression was significantly influenced by the acute phase of IRI. However, plasma apoM levels were not increased in parallel, even slightly decreasing after 0.5 or 1 hour of IRI. We concluded that apoM mRNA expression pattern, like HSP70, in the liver showed rapid, significant changes during hepatic local IRI.

Suppression of apolipoprotein M expression and secretion in alloxan-diabetic mouse: Partial reversal by insulin

We previously reported that apolipoprotein M (apoM) expression is reduced in ob/ ob mice. Whether such a reduction is specific for this model or is a more general phenomenon in diabetes models is not known. In the present study, we therefore investigated apoM expression and secretion in NMRI mice rendered diabetes through administration of alloxan (120 mg/kg). Plasma glucose levels were markedly increased and plasma insulin levels markedly reduced at 3 days after alloxan. At the same time, that plasma apoM concentrations were decreased by 70%, apoM mRNA levels in liver was decreased by 40%, and apoM mRNA in kidney was decreased by 20% in alloxan-treated mice compared to saline-injected controls. Furthermore we found also that daily sc administration of insulin (5 IU/kg per day) increased plasma apoM levels, and apoM mRNA levels in liver and kidney. We therefore conclude that apoM is reduced in this diabetes model and that exogenous insulin administrations partially reverses the abnormal apoM expression. Based on these results, we suggest that insulin regulates apoM synthesis in vivo and, therefore, that the reduction of apoM expression is a general phenomenon in diabetes models.

Leptin inhibits apolipoprotein M transcription and secretion in human hepatoma cell line, HepG2 cells

Apolipoprotein M (apoM) is a novel apolipoprotein presented mostly in high-density lipoprotein (HDL) in human plasma. Previously we have reported that both leptin and leptin receptor are essential for apoM expression in vivo. The expression of apoM is lower in the leptin deficient ( ob/ ob) mouse and leptin receptor deficient ( db/ db) mouse than in the normal mouse. In the present study, however, we demonstrated that supra-physiological concentrations of recombinant leptin significantly inhibited apoM transcription and secretion in the human hepatoma cell line, HepG2 cells. Both Northern blotting and real-time RT-PCR were applied into the analyses of apoM mRNA levels, and compatible data were obtained. The inhibitory effect of leptin on apoM mRNA levels in HepG2 cells is dose dependent, i.e. 100 ng/mL of leptin decreased apoM mRNA levels by 30%, and 500 ng/mL of leptin decreased apoM mRNA levels about 50%. Even at a physiological concentration of leptin (10 ng/mL), apoM expression was decreased, and in parallel, the secretion of apoM into the medium was also decreased. Furthermore, we examined apoAI, apoB and apoE by Northern blotting analyses. The results demonstrated that leptin does not significantly influence the expressions of apoAI, apoB and apoE in HepC2 cells, suggesting that leptin has a specific regulatory effect on hepatic apoM transcription and secretion in vitro. The mechanism on the contradictory effects of leptin on apoM expression in vivo and in vitro needs further investigation.