FOXO1 and LXRα downregulate the apolipoprotein A-I gene expression during hydrogen peroxide-induced oxidative stress in HepG2 cells

Adiponectin Stimulates Apolipoprotein A-1 Gene Expression in HepG2 Cells via AMPK, PPARα, and LXRs Signaling Mechanisms

Adiponectin is an adipose tissue hormone, participating in energy metabolism and involved in atherogenesis. Previously, it was found that adiponectin increases expression of the APOA1 (apolipoprotein A-1) gene in hepatocytes, but the mechanisms of this effect remained unexplored. Our aim was to investigate the role of adiponectin receptors AdipoR1/R2, AMP-activated protein kinase (AMPK), nuclear peroxisome proliferator-activated receptor alpha (PPARα) and liver X receptors (LXRs) in mediating the action of adiponectin on hepatic APOA1 expression in human hepatoma HepG2 cells. The level of APOA1 expression was determined by RT-qPCR and ELISA. We showed that the siRNA-mediated knockdown of genes coding for AdipoR1, AdipoR2, AMPK, PPARα, and LXRα and β prevented adiponectin-induced APOA1 expression in HepG2 cells and demonstrated that interaction of PPARα and LXRs with the APOA1 gene hepatic enhancer is important for the adiponectin-dependent APOA1 transcription. The results of this study point out to the involvement of both types of adiponectin receptors, AMPK, PPARα, and LXRs in the adiponectin-dependent upregulation of the APOA1 expression.

Genetics and regulation of HDL metabolism

The inverse association between plasma HDL cholesterol (HDL-C) levels and risk for cardiovascular disease (CVD) has been demonstrated by numerous epidemiological studies. However, efforts to reduce CVD risk by pharmaceutically manipulating HDL-C levels failed and refused the HDL hypothesis. HDL-C levels in the general population are highly heterogeneous and are determined by a combination of genetic and environmental factors. Insights into the causes of HDL-C heterogeneity came from the study of monogenic HDL deficiency syndromes but also from genome wide association and Μendelian randomization studies which revealed the contribution of a large number of loci to low or high HDL-C cases in the general or in restricted ethnic populations. Furthermore, HDL-C levels in the plasma are under the control of transcription factor families acting primarily in the liver including members of the hormone nuclear receptors (PPARs, LXRs, HNF-4) and forkhead box proteins (FOXO1-4) and activating transcription factors (ATFs). The effects of certain lipid lowering drugs used today are based on the modulation of the activity of specific members of these transcription factors. During the past decade, the roles of small or long non-coding RNAs acting post-transcriptionally on the expression of HDL genes have emerged and provided novel insights into HDL regulation and new opportunities for therapeutic interventions. In the present review we summarize recent progress made in the genetics and the regulation (transcriptional and post-transcriptional) of HDL metabolism.

Regulation of Apolipoprotein A-I Gene Expression in Human Macrophages by Oxidized Low-Density Lipoprotein

Apolipoprotein A-I (ApoA-I) is a key component of reverse cholesterol transport in humans. In the previous studies, we demonstrated expression of the apoA-I gene in human monocytes and macrophages; however, little is known on the regulation of the apoA-I expression in macrophages during the uptake of modified low-density lipoprotein (LDL), which is one of the key processes in the early stages of atherogenesis leading to formation of foam cells. Here, we demonstrate a complex nature of the apoA-I regulation in human macrophages during the uptake of oxidized LDL (oxLDL). Incubation of macrophages with oxLDL induced expression of the apoA-I gene within the first 24 hours, but suppressed it after 48 h. Both effects depended on the interaction of oxLDL with the TLR4 receptor, rather than on the oxLDL uptake by the macrophages. The oxLDL-mediated downregulation of the apoA-I gene depended on the ERK1/2 and JNK cascades, as well as on the NF-κB cascade.

MiR-135a-5p inhibits vascular smooth muscle cells proliferation and migration by inactivating FOXO1 and JAK2 signaling pathway

BACKGROUND

It is reportedly demonstrated that miR-135a-5p plays a critical role in cancer cells, macrophages, and endothelia cells. However, little is known concerning the function of miR-135a-5p in vascular smooth muscle cells (VSMCs) and atherosclerosis (AS).

METHODS

Human VSMCs and male C57BL/6 mice were used for establishing AS cell models and animal models. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to detect the expressions of miR-135a-5p, forkhead box O1 (FOXO1) mRNA, and Janus kinase 2 (JAK2) mRNA. CCK-8, BrdU, and Transwell assays were used to detect cell migration and proliferation. Cell cycle and apoptosis were analyzed using flow cytometry. The interactions among miR-135a-5p, FOXO1 and JAK2 were validated employing Western blot, qRT-PCR and Luciferase reporter gene assay.

RESULTS

The expression of miR-135a-5p was significantly decreased in serum samples of AS patients, VSMCs treated with ox-LDL and AS mice models. The overexpression of miR-135a-5p induced VSMCs cycle arrest and apoptosis, and inhibited proliferation and migration. Further experiments confirmed that miR-135a-5p could target and repress FOXO1/CyclinD1 and JAK2/STAT3 pathway. Additionally, the associations among miR-135a-5p, FOXO1/Cyclin D1 and JAK2/STAT3 were validated using animal models.

CONCLUSION

MiR-135a-5p suppresses VSMCs proliferation and migration induced by ox-LDL via targeting and activating FOXO1/Cyclin D1 and JAK2/STAT3 signaling pathways.

Association of genetic polymorphisms in SOD2, SOD3, GPX3, and GSTT1 with hypertriglyceridemia and low HDL-C level in subjects with high risk of coronary artery disease

Background

Oxidative stress modulates insulin resistant-related atherogenic dyslipidemia: hypertriglyceridemia (HTG) and low high-density lipoprotein cholesterol (HDL-C) level. Gene polymorphisms in superoxide dismutase (SOD2 and SOD3), glutathione peroxidase-3 (GPX3), and glutathione S-transferase theta-1 (GSTT1) may enable oxidative stress-related lipid abnormalities and severity of coronary atherosclerosis. The present study investigated the associations of antioxidant-related gene polymorphisms with atherogenic dyslipidemia and atherosclerotic severity in subjects with high risk of coronary artery disease (CAD).

Methods

Study population comprises of 396 subjects with high risk of CAD. Gene polymorphisms: SOD2 rs4880, SOD3 rs2536512 and rs2855262, GPX rs3828599, and GSTT1 (deletion) were evaluated the associations with HTG, low HDL-C, high TG/HDL-C ratio, and severity of coronary atherosclerosis.

Results

SOD2 rs4880-CC, SOD3 rs2536512-AA, rs2855262-CC, and GPX3 rs3828599-AA, but not GSTT1^-/- individually increased risk of HTG combined with low HDL-C level. With a combination of five risk-genotypes as a genetic risk score (GRS), GRS ≥ 6 increased risks of low HDL-C, high TG/HDL-C ratio, and HTG combined with low HDL-C, comparing with GRS 0–2 [respective adjusted ORs (95% CI) = 2.70 (1.24–5.85), 3.11 (1.55–6.23), and 5.73 (2.22–14.77)]. Gene polymorphisms, though, were not directly associated with severity of coronary atherosclerosis; high TG/HDL-C ratio was associated with coronary atherosclerotic severity [OR = 2.26 (95% CI [1.17–4.34])].

Conclusion

Combined polymorphisms in antioxidant-related genes increased the risk of dyslipidemia related to atherosclerotic severity, suggesting the combined antioxidant-related gene polymorphisms as predictor of atherogenic dyslipidemia.

The protective effect of beta-casomorphin-7 via promoting Foxo1 activity and nuclear translocation in human lens epithelial cells

PURPOSE

To investigate the protective effect of beta-casomorphin-7 (β-CM-7) in oxidative stressed human lens epithelial cells (HLECs) and to explore the possible mechanism for oxidative stress in HLECs induced by high glucose.

METHODS

We used HLECs to determine the effect of different concentrations of β-CM-7 on cell viability by 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolimol/L bromide (MTT) assay. We used flow cytometry to determine the content of reactive oxygen species (ROS) induced by oxidative stress and a bioassay kit to determine the oxidant malondialdehyde (MDA) and antioxidant enzyme superoxide dismutase (SOD) levels. We used Western blotting and an immunofluorescence assay to determine the expression of Forkhead box o1 (Foxo1), SP1, and the related protein glutathione peroxidase (GSH-px) at the molecular biology level as well as their intracellular localization.

RESULTS

The expression of Foxo1 and SP1 was weakly expressed when the glucose concentration was 40 mM/L, but was highly expressed when cells were pre-treated with an appropriate concentration of β-CM-7. After pre-treatment with β-CM-7, the cells treated with 40 mM/L glucose for 48 h showed Foxo1 was transferred to the nucleus, and the expression of SP1 was increased. The content of ROS and MDA in the HLECs that were pre-treated with β-CM-7 was lower than in those that was not pre-treated (p <0.05). Accordingly, SOD was elevated in the cells pre-treated with β-CM-7. The relative expression of GSH-px increased with increases of Foxo1 and SP1.

CONCLUSION

β-CM-7 protects HLECs from oxidative damage by upregulating the relative expression of Foxo1 and promoting Foxo1 nuclear translocation.

Tumor necrosis factor α stimulates endogenous apolipoprotein A-I expression and secretion by human monocytes and macrophages: role of MAP-kinases, NF-κB, and nuclear receptors PPARα and LXRs

Apolipoprotein A-I (ApoA-I) is the main structural and functional protein component of high-density lipoprotein. ApoA-I has been shown to regulate lipid metabolism and inflammation in macrophages. Recently, we found the moderate expression of endogenous apoA-I in human monocytes and macrophages and showed that pro-inflammatory cytokine tumor necrosis factor α (TNFα) increases apoA-I mRNA and stimulates ApoA-I protein secretion by human monocytes and macrophages. Here, we present data about molecular mechanisms responsible for the TNFα-mediated activation of apoA-I gene in human monocytes and macrophages. This activation depends on JNK and MEK1/2 signaling pathways in human monocytes, whereas inhibition of NFκB, JNK, or p38 blocks an increase of apoA-I gene expression in the macrophages treated with TNFα. Nuclear receptor PPARα is a ligand-dependent regulator of apoA-I gene, whereas LXRs stimulate apoA-I mRNA transcription and ApoA-I protein synthesis and secretion by macrophages. Treatment of human macrophages with PPARα or LXR synthetic ligands as well as knock-down of LXRα, and LXRβ by siRNAs interfered with the TNFα-mediated activation of apoA-I gene in human monocytes and macrophages. At the same time, TNFα differently regulated the levels of PPARα, LXRα, and LXRβ binding to the apoA-I gene promoter in THP-1 cells. Obtained results suggest a novel tissue-specific mechanism of the TNFα-mediated regulation of apoA-I gene in monocytes and macrophages and show that endogenous ApoA-I might be positively regulated in macrophage during inflammation.

Physical and functional interactions between nuclear receptor LXRα and the forkhead box transcription factor FOXA2 regulate the response of the human lipoprotein lipase gene to oxysterols in hepatic cells

Lipoprotein lipase (LPL) catalyzes the hydrolysis of triglycerides from triglyceride-rich lipoproteins such as VLDL and chylomicrons in the circulation. Mutations in LPL or its activator apolipoprotein C-II cause hypertriglyceridemia in humans and animal models. The levels of LPL in the liver are low but they can be strongly induced by a high cholesterol diet or by synthetic ligands of Liver X Receptors (LXRs). However, the mechanism by which LXRs activate the human LPL gene is unknown. In the present study we show that LXR agonists increased the mRNA and protein levels as well as the promoter activity of human LPL in HepG2 cells. A promoter deletion analysis defined the proximal -109/-28 region, which contains a functional FOXA2 element, as essential for transactivation by ligand-activated LXRα/RXRα heterodimers. Silencing of endogenous FOXA2 in HepG2 cells by siRNAs or by treatment with insulin compromised the induction of the LPL gene by LXR agonists whereas mutations in the FOXA2 site abolished the synergistic transactivation of the LPL promoter by LXRα/RXRα and FOXA2. Physical and functional interactions between LXRα and FOXA2 were established in vitro and ex vivo. In summary, the present study revealed a novel mechanism of human LPL gene induction by oxysterols in the liver with is based on physical and functional interactions between transcription factors LXRα and FOXA2. This mechanism, which may not be restricted to the LPL gene, is critically important for a better understanding of the regulation of cholesterol and triglyceride metabolism in the liver under healthy or pathological states.

Diabetes and dyslipidemia: characterizing lipoprotein metabolism

Premature atherosclerosis in diabetes accounts for much of the decreased life span. New treatments have reduced this risk considerably. This review explores the relationship among the disturbances in glucose, lipid, and bile salt metabolic pathways that occur in diabetes. In particular, excess nutrient intake and starvation have major metabolic effects, which have allowed us new insights into the disturbance that occurs in diabetes. Metabolic regulators such as the forkhead transcription factors, the farnesyl X transcription factors, and the fibroblast growth factors have become important players in our understanding of the dysregulation of metabolism in diabetes and overnutrition. The disturbed regulation of lipoprotein metabolism in both the intestine and the liver has been more clearly defined over the past few years, and the atherogenicity of the triglyceride-rich lipoproteins, and - in tandem - low levels of high-density lipoproteins, is seen now as very important. New information on the apolipoproteins that control lipoprotein lipase activity has been obtained. This is an exciting time in the battle to defeat diabetic atherosclerosis.