Upregulation of LncRNA UCA1 promotes cardiomyocyte proliferation by inhibiting the miR-128/SUZ12/P27 pathway.

Enhancing cardiomyocyte proliferation is essential to reverse or slow down the heart failure progression in many cardiovascular diseases such as myocardial infarction (MI). Long non-coding RNAs (lncRNAs) have been reported to regulate cardiomyocyte proliferation. In particular, lncRNA urothelial carcinoma-associated 1 (lncUCA1) played multiple roles in regulating cell cycle progression and cardiovascular diseases, making lncUCA1 a potential target for promoting cardiomyocyte proliferation. However, the role of lncUCA1 in cardiomyocyte proliferation remains unknown. This study aimed at exploring the function and underlying molecular mechanism of lncUCA1 in cardiomyocyte proliferation. Quantitative RT-PCR showed that lncUCA1 expression decreased in postnatal hearts. Gain-and-loss-of-function experiments showed that lncUCA1 positively regulated cardiomyocyte proliferation in vitro and in vivo. The bioinformatics program identified miR-128 as a potential target of lncUCA1, and loss of miR-128 was reported to promote cardiomyocyte proliferation by inhibiting the SUZ12/P27 pathway. Luciferase reporter assay, qRT-PCR, western blotting, and immunostaining experiments further revealed that lncUCA1 acted as a ceRNA of miR-128 to upregulate its target SUZ12 and downregulate P27, thereby increasing cyclin B1, cyclin E, CDK1 and CDK2 expression to promote cardiomyocyte proliferation. In conclusion, upregulation of lncRNA UCA1 promoted cardiomyocyte proliferation by inhibiting the miR-128/SUZ12/P27 pathway. Our results indicated that lncUCA1 might be a new therapeutic target for stimulating cardiomyocyte proliferation.

Ilexgenin A inhibits lipid accumulation in macrophages and reduces the progression of atherosclerosis through PTPN2/ERK1/2/ABCA1 signalling pathway.

Macrophage lipid accumulation indicates a pathological change in atherosclerosis. Ilexgenin A (IA), a pentacyclic triterpenoid compound, plays a role in preventing inflammation, bacterial infection, and fatty liver and induces a potential anti-atherogenic effect. However, the anti-atherosclerotic mechanism remains unclear. The present study investigated the effects of IA on lipid accumulation in macrophage-derived foam cells and atherogenesis in apoE-/- mice. Our results indicated that the expression of adenosine triphosphate-binding cassette transporter A1 (ABCA1) was up-regulated by IA, promoting cholesterol efflux and reducing lipid accumulation in macrophages, which may be regulated by the protein tyrosine phosphatase non-receptor type 2 (PTPN2)/ERK1/2 signalling pathway. IA attenuated the progression of atherosclerosis in high-fat diet-fed apoE-/- mice. PTPN2 knockdown with siRNA or treatment with an ERK1/2 agonist (Ro 67-7476) impeded the effects of IA on ABCA1 upregulation and cholesterol efflux in macrophages. These results suggest that IA inhibits macrophage lipid accumulation and alleviates atherosclerosis progression via the PTPN2/ERK1/2 signalling pathway.

Gut microbiota and immune mediation: a Mendelian randomization study on granulomatosis with polyangiitis.

Background: The gut microbiota plays a pivotal role in influencing various health outcomes, including immune-mediated conditions. Granulomatosis with Polyangiitis (GPA) is one such condition, and its potential associations with gut microbiota remain underexplored. Method: Using a two-sample Mendelian randomization approach, we investigated the causal links between gut microbiota and GPA. We sourced our data from multiple cohorts and consortiums, including the MiBioGen consortium. Our study design incorporated both direct associations and mediation effects of immune traits on the relationship between gut microbiota and GPA. Results: Our analysis revealed significant associations between 1 phylum, 1 family 9 genus microbiota taxa and GPA. Furthermore, we identified several immune cell traits that mediated the effects of gut microbiota on GPA. For instance, the family Defluviitaleaceae and genus Defluviitaleaceae UCG011 influenced GPA through CD11c in granulocytes. The mediation effect proportions further elucidated the complex dynamics between gut microbiota exposures, immune markers, and their combined influence on GPA. Conclusion: Our findings underscore the intricate relationship between gut microbiota, immune markers, and GPA. The identified associations and mediation effects provide valuable insights into the potential therapeutic avenues targeting gut microbiota to manage GPA.

Pax-8: Molecular biology, pathophysiology, and potential pathogenesis.

Transcription factors, as the convergence points of multiple signaling pathways in eukaryotic cells, are closely involved in disease development. Pax-8, an important transcription factor belonging to the Pax family, exerts a crucial influence on the regulation of gene expression required for both physiological conditions and pathological processes. Pax-8 contributes to the pathogenesis of many human diseases, ranging from cardiovascular disease to many cancers, and therefore, it can be imagined that Pax-8 holds great therapeutic potential. In this review, we summarize the structure, distribution, function, and regulatory mechanisms of Pax-8 to provide a new research direction for Pax-8.

Genetic Variants of CYP4F2 Associated with Ischemic Stroke Susceptibility in the Han Population from Southern China.

Background: The pathophysiological mechanism of ischemic stroke is complex. Traditional risk factors cannot fully or only partially explain the occurrence and development of IS. Genetic factors are getting more and more attention. Our study aimed to explore the association between CYP4F2 gene polymorphism and susceptibility to IS. Methods: A total of 1322 volunteers were enrolled to perform an association analysis through SNPStats online software. Using FPRP (false-positive report probability) to detect whether the result is a noteworthy finding. The interaction of SNP-SNP in IS risk was assessed by multi-factor dimensionality reduction. Statistical analysis of this study was mainly completed by SPSS 22.0 software. Results: Mutant allele "A" (OR = 1.24) and genotype "AA" (OR = 1.49) or "GA" (OR = 1.26) of CYP4F2-rs2108622 are risk genetic factors for IS. Rs2108622 is significantly associated with an increased risk of IS among subjects who are females, aging >60 years old, with BMI ≥24 kg/m2, and smoking or drinking volunteers. CYP4F2-rs3093106 and -rs3093105 are associated with susceptibility to IS among smoking, drinking subjects, or IS patients complicated with hypertension. Conclusion: CYP4F2-rs2108622, -rs3093106, and -rs3093105 are associated with an increased risk of IS.

The prevalence of coronary atherosclerosis in patients with refractory gastroesophageal reflux disease ready for antireflux surgery.

Coronary atherosclerosis (CAS) and gastroesophageal reflux disease (GERD) share common risk factors. The existing CAS may not only increase the possibility of GERD to be refractory GERD (RGERD), but also increase the risk of antireflux surgery for these patients. The aim of this study was to estimate the prevalence of CAS and its potential risk factors in patients with RGERD ready for antireflux surgery. The retrospective analysis was performed in the digestive disease center of Suining Central Hospital, a teritary hospital in Sichuan, China. Records of patients with RGERD admitted to the hospital for antireflux surgery between July 2018, and June 2021 were included. The included patients were divided into the RGERD group and RGERD-CAS group based on the coronary computed tomography angiography (CCTA) results, which were defined as no CAS and CAS (<50% mild stenosis or ≥50% significant stenosis). In total, 448 patients with RGERD qualified for the study. The prevalence of CAS in these patients was 45.1%. Specifically, 246 patients (54.9%) were in the RGERD group, and 202 patients (45.1%) were in the RGERD-CAS group. Among these 202 patients with CAS, 120 patients (59.4%) had mild CAS (<50% stenosis), 82 patients (40.6%) had significant CAS (≥50% stenosis). Five independent risk factors, including male sex, high blood pressure (HBP), diabetes mellitus (DM), Barrett's esophagus (BE) and family history of coronary artery disease were identified for the occurrence of CAS in patients with RGERD ready for antireflux surgery after adjusting for other factors. CAS is prevalent in patients with RGERD ready for antireflux surgery. Routing CTTA was suggested to exclude potential coronary artery disease in RGERD patients ready for antireflux surgery with independent risk factors.

Metoprolol Protects Against Arginine Vasopressin-Induced Cellular Senescence in H9C2 Cardiomyocytes by Regulating the Sirt1/p53/p21 Axis.

Cardiomyocyte senescence is involved in the pathological mechanism of cardiac diseases. Metoprolol is a ß1 receptor blocker used for the treatment of hypertension. Recent studies show that Metoprolol can protect cardiomyocytes against ischemia injury. The present study aims to investigate the protective effects of Metoprolol against arginine vasopressin (AVP)-induced cellular senescence in cultured cardiomyocytes. The cell proliferation assay and cytotoxicity lactate dehydrogenase assay showed that the highest tolerated dosage of Metoprolol in H9C2 cardiomyocytes was optimized as 10 µM. The enzyme-linked immunosorbent assay showed that Metoprolol significantly ameliorated the elevated level of the DNA oxidation product 8-hydroxy-2 deoxyguanosine. Metoprolol also decreased the percentage of senescence-associated ß-galactosidase positive cells and improved the telomerase activity under AVP exposure. Moreover, treatment with Metoprolol ameliorated the decreased intracellular nicotinamide phosphoribosyltransferase activity, nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide phosphate (NAD+/NADPH) ratio, and Sirtuin1 activity in cardiomyocytes by AVP. Finally, Metoprolol was able to downregulate the AVP-induced expression of acetylated p53 and p21. Taken together, our data reveal that Metoprolol protected the cardiomyocytes from AVP-induced senescence.

Myristica fragrans promotes ABCA1 expression and cholesterol efflux in THP-1-derived macrophages.

Myristica fragrans is a traditional herbal medicine and has been shown to alleviate the development of atherosclerosis. However, the anti-atherogenic mechanisms of M. fragrans are still to be addressed. In this study, we explored the effect of M. fragrans on lipid metabolism and inflammation and its mechanisms in THP-1-derived macrophages. The quantitative polymerase chain reaction and western blot analysis results showed that M. fragrans promotes cholesterol efflux from THP-1-derived macrophages and reduces intracellular total cholesterol, cholesterol ester, and free cholesterol contents in a dose- and a time-dependent manner. Further study found that liver X receptor alpha (LXRα) antagonist GGPP significantly blocked the upregulation of ABCA1 expression with M. fragrans treatment. In addition, chromatin immunoprecipitation assay confirmed that GATA binding protein 3 (GATA3) can bind to the LXRα promoter, and inhibition of GATA3 led to the downregulation of LXRα and ATP-binding cassette subfamily A member 1 expression. Furthermore, M. fragrans reduced lipid accumulation, followed by decreasing tumor necrosis factor-α, interleukin (IL)-6, and IL-1ß and increasing IL-10 produced by THP-1-derived macrophages. Therefore, M. fragrans is identified as a valuable therapeutic medicine for atherosclerotic cardiovascular disease.

Pregnancy-Associated Plasma Protein-A Accelerates Atherosclerosis by Regulating Reverse Cholesterol Transport and Inflammation.

BACKGROUND: Recent studies have suggested that pregnancy-associated plasma protein-A (PAPP-A) is involved in the pathogenesis of atherosclerosis. This study aim is to investigate the role and mechanisms of PAPP-A in reverse cholesterol transport (RCT) and inflammation during the development of atherosclerosis. Methods and Results: PAPP-A was silenced in apolipoprotein E (apoE-/-) mice with administration of PAPP-A shRNA. Oil Red O staining of the whole aorta root revealed that PAPP-A knockdown reduced lipid accumulation in aortas. Oil Red O, hematoxylin and eosin (HE) and Masson staining of aortic sinus further showed that PAPP-A knockdown alleviated the formation of atherosclerotic lesions. It was found that PAPP-A knockdown reduced the insulin-like growth factor 1 (IGF-1) levels and repressed the PI3K/Akt pathway in both aorta and peritoneal macrophages. The expression levels of LXRα, ABCA1, ABCG1, and SR-B1 were increased in the aorta and peritoneal macrophages from apoE-/-mice administered with PAPP-A shRNA. Furthermore, PAPP-A knockdown promoted RCT from macrophages to plasma, the liver, and feces in apoE-/-mice. In addition, PAPP-A knockdown elevated the expression and secretion of monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6), tumor necrosis factor-α, and interleukin-1ß through the nuclear factor kappa-B (NF-κB) pathway. CONCLUSIONS: The present study results suggest that PAPP-A promotes the development of atherosclerosis in apoE-/-mice through reducing RCT capacity and activating an inflammatory response.

Chlamydia pneumoniae negatively regulates ABCA1 expression via TLR2-Nuclear factor-kappa B and miR-33 pathways in THP-1 macrophage-derived foam cells.

OBJECTIVES: ATP-binding cassette transporter A1 (ABCA1) is critical in exporting cholesterol from macrophages and plays a protective role in the development of atherosclerosis. This study was to determine the effects and potential mechanisms of Chlamydia pneumoniae (C. pneumoniae) on ABCA1 expression and cellular cholesterol efflux in THP-1 macrophage-derived foam cells. METHODS AND RESULTS: C. pneumoniae significantly decreased the expression of ABCA1 and reduced cholesterol efflux. Furthermore, we found that C. pneumoniae suppressed ABCA1 expression via up-regulation of miR-33s. The inhibition of C. pneumoniae-induced NF-κB activation decreased miR-33s expression and enhanced ABCA1 expression. In addition, C. pneumoniae increased Toll-like receptor 2 (TLR2) expressions, inhibition of which by siRNA could also block NF-κB activation and miR-33s expression, and promot the expression of ABCA1. CONCLUSION: Taken together, these results reveal that C. pneumoniae may negatively regulate ABCA1 expression via TLR2-NF-κB and miR-33 pathways in THP-1 macrophage-derived foam cells, which may provide new insights for understanding the effects of C. pneumoniae on the pathogenesis of atherosclerosis.

MicroRNA-27a/b regulates cellular cholesterol efflux, influx and esterification/hydrolysis in THP-1 macrophages.

RATIONALE: Macrophage cholesterol homeostasis maintenance is the result of a balance between influx, endogenous synthesis, esterification/hydrolysis and efflux. Excessive accumulation of cholesterol leads to foam cell formation, which is the major pathology of atherosclerosis. Previous studies have shown that miR-27 (miR-27a and miR-27b) may play a key role in the progression of atherosclerosis. OBJECTIVE: We set out to investigate the molecular mechanisms of miR-27a/b in intracellular cholesterol homeostasis. METHODS AND RESULTS: In the present study, our results have shown that the miR-27 family is highly conserved during evolution, present in mammals and directly targets the 3' UTR of ABCA1, LPL, and ACAT1. apoA1, ABCG1 and SR-B1 lacking miR-27 bind sites should not be influenced by miR-27 directly. miR-27a and miR-27b directly regulated the expression of endogenous ABCA1 in different cells. Treatment with miR-27a and miR-27b mimics reduced apoA1-mediated cholesterol efflux by 33.08% and 44.61% in THP-1 cells, respectively. miR-27a/b also regulated HDL-mediated cholesterol efflux in THP-1 macrophages and affected the expression of apoA1 in HepG2 cells. However, miR-27a/b had no effect on total cellular cholesterol accumulation, but regulated the levels of cellular free cholesterol and cholesterol ester. We further found that miR-27a/b regulated the expression of LPL and CD36, and then affected the ability of THP-1 macrophages to uptake Dil-oxLDL. Finally, we identified that miR-27a/b regulated cholesterol ester formation by targeting ACAT1 in THP-1 macrophages. CONCLUSION: These findings indicate that miR-27a/b affects the efflux, influx, esterification and hydrolysis of cellular cholesterol by regulating the expression of ABCA1, apoA1, LPL, CD36 and ACAT1.

Growth differentiation factor-15 induces expression of ATP-binding cassette transporter A1 through PI3-K/PKCζ/SP1 pathway in THP-1 macrophages.

OBJECTIVE: The aim of this study was to determine whether ATP-binding cassette transporter A1 (ABCA1) was up-regulated by growth differentiation factor-15 (GDF-15) via the phosphoinositide 3-kinase (PI3K)/protein kinase Cζ (PKCζ)/specificity protein 1 (SP1) pathway in THP-1 macrophages. METHODS AND RESULTS: We investigated the effects of different concentrations of GDF-15 on ABCA1 expression in THP-1 macrophages. The results showed that GDF-15 dramatically increased cholesterol efflux and decreased cellular cholesterol levels. In addition, GDF15 increased ABCA1 mRNA and protein levels. The effects of GDF-15 on ABCA1 protein expression and cellular cholesterol efflux were abolished by wither inhibition or depletion of PI3K, PKCζ and SP1, respectively, suggesting the potential roles of PI3K, PKCζ and SP1 in ABCA1 expression. Taken together, GDF-15 appears to activate PI3K, PKCζ and SP1 cascade, and then increase ABCA1 expression, thereby promoting cholesterol efflux and reducing foam cell formation. CONCLUSION: Our results suggest that GDF-15 has an overall protective effect on the progression of atherosclerosis, likely through inducing ABCA1 expression via the PI3K/PKCζ/SP1 signaling pathway and enhancing cholesterol efflux.

Apelin and its receptor APJ in cardiovascular diseases.

Apelin is an adipokine that has been identified as an endogenous ligand for the orphan receptor APJ. Apelin and APJ are expressed in a diverse range of tissues with particular preponderance for the heart and vasculature. Apelin has powerful positive inotropic actions and causes endothelium- and nitric oxide-dependent vasodilatation. Growing evidence shows that apelin/APJ system functions as a critical mediator of cardiovascular homeostasis and is involved in the pathophysiology of cardiovascular diseases. Targeting apelin/APJ axis produces protection against cardiovascular diseases. In the current review we have summarized recent data concerning the role and therapeutic potential of apelin/APJ in several major cardiovascular diseases. An increased understanding of the cardiovascular actions of apelin/APJ system will help to develop novel therapeutic interventions for cardiovascular diseases.

The effects of miR-467b on lipoprotein lipase (LPL) expression, pro-inflammatory cytokine, lipid levels and atherosclerotic lesions in apolipoprotein E knockout mice.

Atherosclerosis is a lipid disorder disease characterized by chronic blood vessel wall inflammation driven by the subendothelial accumulation of macrophages. Studies have shown that lipoprotein lipase (LPL) participates in lipid metabolism, but it is not yet known whether post-transcriptional regulation of LPL gene expression by microRNAs (miRNAs) occurs in vivo. Here, we tested that miR-467b provides protection against atherosclerosis by regulating the target gene LPL which leads to reductions in LPL expression, lipid accumulation, progression of atherosclerosis and production of inflammatory cytokines in apolipoprotein E knockout (apoE(-/-)) mice. Treatment of apoE(-/-) mice with intra-peritoneal injection of miR-467b agomir led to decreased blood plasma levels of total cholesterol (TC), triglyceride (TG), low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), IL-1ß and monocyte chemotactic protein-1 (MCP-1). Using Western blots and real time PCR, we determined that LPL expression in aorta and abdominal cavity macrophages were significantly down-regulated in the miR-467b agomir group. Furthermore, systemic treatment with miR-467b antagomir accelerated the progression of atherosclerosis in the aorta of apoE(-/-) mice. The present study showed that miR-467b protects apoE(-/-) mice from atherosclerosis by reducing lipid accumulation and inflammatory cytokine secretion via downregulation of LPL expression. Therefore, targeting miR-467b may offer a promising strategy to treat atherosclerotic vascular disease.

Antagonism of betulinic acid on LPS-mediated inhibition of ABCA1 and cholesterol efflux through inhibiting nuclear factor-kappaB signaling pathway and miR-33 expression.

ATP-binding cassette transporter A1 (ABCA1) is critical in exporting cholesterol from macrophages and plays a protective role in the development of atherosclerosis. The purpose of this study was to investigate the effects of betulinic acid (BA), a pentacyclic triterpenoid, on ABCA1 expression and cholesterol efflux, and to further determine the underlying mechanism. BA promoted ABCA1 expression and cholesterol efflux, decreased cellular cholesterol and cholesterol ester content in LPS-treated macrophages. Furthermore, we found that BA promoted ABCA1 expression via down-regulation of miR-33s. The inhibition of LPS-induced NF-κB activation further decreased miR-33s expression and enhanced ABCA1 expression and cholesterol efflux when compared with BA only treatment. In addition, BA suppressed IκB phosphorylation, p65 phosphorylation and nuclear translocation, and the transcription of NF-κB-dependent related gene. Moreover, BA reduced atherosclerotic lesion size, miR-33s levels and NF-κB activation, and promoted ABCA1 expression in apoE(-/-) mice. Taken together, these results reveal a novel mechanism for the BA-mediated ABCA1 expression, which may provide new insights for developing strategies for modulating vascular inflammation and atherosclerosis.

Tertiary-butylhydroquinone upregulates expression of ATP-binding cassette transporter A1 via nuclear factor E2-related factor 2/heme oxygenase-1 signaling in THP-1 macrophage-derived foam cells.

BACKGROUND: Tert-butylhydroquinone (tBHQ), a synthetic phenolic antioxidant, is commonly used as a food preservative because of its potent antilipid peroxidation activity. Several lines of evidence have demonstrated that dietary supplementation with antioxidants has an antiatherogenic function through reducing cholesterol uptake or promoting reverse cholesterol transport. In this study, we investigated whether tBHQ affects expression of ATP-binding cassette transporter A1 (ABCA1) and the potential subsequent effect on cellular cholesterol homeostasis. METHODS AND RESULTS: tBHQ increased ABCA1 protein levels and markedly enhanced cholesterol efflux from THP-1 macrophage-derived foam cells. Furthermore, tBHQ reduced calpain-mediated ABCA1 proteolysis via activation of nuclear factor E2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1). Inhibition of HO-1 with a pharmacological inhibitor or siRNA and knockdown of Nrf2 suppressed the stimulatory effects of tBHQ on ABCA1 expression and calpain activity. CONCLUSIONS: Nrf2/HO-1 signaling is required for the regulation by tBHQ of ABCA1 expression and cholesterol efflux in macrophage-derived foam cells and an antiatherogenic role of tBHQ is suggested.

Apelin-13 increases expression of ATP-binding cassette transporter A1 via activating protein kinase C α signaling in THP-1 macrophage-derived foam cells.

Apelin has an antiatherogenic function through activating protein kinase C (PKC) to initiate a series of cellular signaling pathways. PKC phosphorylates and stabilizes ATP-binding cassette transporter A1 (ABCA1) through inhibiting its degradation mediated by calpain. Thus, in the present study, we investigated whether apelin-13 affects expression of ABCA1 through PKC signaling. The results showed that apelin-13 dramatically increased cholesterol efflux from THP-1 macrophage-derived foam cells and reduced cellular cholesterol levels. ABCA1 protein but not mRNA levels were dramatically increased by apelin-13, and calpain-induced degradation of ABCA1 and calpain activity were suppressed with treatment of apelin-13. However, the effects of apelin-13 on ABCA1 protein expression, cellular cholesterol efflux and calpain activity were abolished by depletion of PKCα, suggesting the potential important role of PKCα. In addition, apelin-13 was shown to phosphorylate serine residues in ABCA1 through the PKCα pathway. Thus, apelin-13 appears to activate PKCα, phosphorylate ABCA1 and inhibit calpain-mediated proteolysis, thereby promoting cholesterol efflux and reducing foam cell formation. Our study herein described a possible mechanism for understanding the antiatherogenic effects of apelin on attenuating the progression of atherosclerosis.

MicroRNA-467b targets LPL gene in RAW 264.7 macrophages and attenuates lipid accumulation and proinflammatory cytokine secretion.

LPL (lipoprotein lipase) is a rate-limiting enzyme involved in the hydrolysis of triglycerides. Previous studies have shown that microRNA (miR)-467b regulates hepatic LPL expression and plays a role in the progression of steatosis or abnormal lipid retention in obese mice. Macrophage-derived LPL has been shown to promote atherosclerosis. However, if miR-476b influences macrophage LPL expression and the subsequent effects are unknown. Here, we utilized oxLDL-treatment RAW 264.7 macrophages that were transfected with miR-467b mimics or inhibitors to investigate the potential roles of macrophage miR-476b. We found that miR-467b significantly decreased lipid accumulation and IL-6, IL-1ß, TNF-α and MCP-1 secretions. Furthermore, our studies suggested an additional explanation for the regulatory mechanism of miR-467b on its functional target, LPL in RAW 264.7 macrophages. Thus, our findings indicate that miR-467b may regulate lipid accumulation and proinflammatory cytokine secretion in oxLDL-stimulated RAW 264.7 macrophages by targeting the LPL gene.

PAPP-A negatively regulates ABCA1, ABCG1 and SR-B1 expression by inhibiting LXRα through the IGF-I-mediated signaling pathway.

Pregnancy-associated plasma protein-A (PAPP-A) has been involved in the atherosclerotic process through regulation of local expression of IGF-1 that mediates the activation of the phosphatidylinositol-3 (PI3-K) and Akt kinase (Akt) signaling cascades which lead to constitutive nitric oxide formation, with its attending vasodilator, antiplatelet and insulin-sensitizing actions. In addition, IGF-1 may decreased cholesterol efflux through reductions of expression in ABCA1 and SR-B1 by the PI3-K/Akt signaling pathway. In the current study, we examined whether PAPP-A was involved in LXRα regulation and in expression of ABCA1, ABCG1 or SR-B1 through the IGF-I-mediated signaling pathway (IGF/PI3-K/Akt). Results showed that PAPP-A significantly decreased expression of ABCA1, ABCG1 and SR-BI at both transcriptional and translational levels in a dose-dependent and time-dependent manner. Cellular cholesterol content was increased while cholesterol efflux was decreased by PAPP-A treatment. Moreover, LXRα which can regulate the expression of ABCA1, ABCG1 and SR-B1, was also down-regulated by PAPP-A treatment. LXRα-specific activation by LXRα agonist almost rescued the down-regulation of ABCA1, ABCG1 and SR-B1 expression by PAPP-A. In addition, PAPP-A can induce the IGF-1/PI3-K/Akt pathway in macrophages. Furthermore, our results indicate that the decreased levels observed in LXRα, ABCA1, ABCG1 and SR-B1 mRNA and protein levels upon treating cells with PAPP-A were strongly impaired with the PI3-K inhibitors or IGF-1R siRNA while the MAPK cascade inhibitor did not execute this effect, indicating that the process of ABCA1, ABCG1 and SR-BI degradation by PAPP-A involves the IGF-1/PI3-K/Akt pathway. In conclusion, PAPP-A may first down-regulate expression of LXRα through the IGF-1/PI3-K/Akt signaling pathway and then decrease expression of ABCA1, ABCG1, SR-B1 and cholesterol efflux in THP-1 macrophage-derived foam cells. Therefore, our study provided one of the mechanisms for understanding the critical effect of PAPP-A in pathogenesis of atherosclerosis.