Liver X receptor activator downregulates angiotensin II type 1 receptor expression through dephosphorylation of Sp1

Role of post-translational modifications of Sp1 in cardiovascular diseases

Specific protein 1 (Sp1) is pivotal in sustaining baseline transcription as well as modulating cell signaling pathways and transcription factors activity. Through interactions with various proteins, especially transcription factors, Sp1 controls the expression of target genes, influencing numerous biological processes. Numerous studies have confirmed Sp1's significant regulatory role in the pathogenesis of cardiovascular disorders. Post-translational modifications (PTMs) of Sp1, such as phosphorylation, ubiquitination, acetylation, glycosylation, SUMOylation, and S-sulfhydration, can enhance or modify its transcriptional activity and DNA-binding stability. These modifications also regulate Sp1 expression across different cell types. Sp1 is crucial in regulating non-coding gene expression and the activity of proteins in response to pathophysiological stimuli. Understanding Sp1 PTMs advances our knowledge of cell signaling pathways in controlling Sp1 stability during cardiovascular disease onset and progression. It also aids in identifying novel pharmaceutical targets and biomarkers essential for preventing and managing cardiovascular diseases.

Role of Sp1 in atherosclerosis

Specificity protein (Sp) is a famous family of transcription factors including Sp1, Sp2 and Sp3. Sp1 is the first one of Sp family proteins to be characterized and cloned in mammalian. It has been proposed that Sp1 acts as a modulator of the expression of target gene through interacting with a series of proteins, especially with transcriptional factors, and thereby contributes to the regulation of diverse biological processes. Notably, growing evidence indicates that Sp1 is involved in the main events in the development of atherosclerosis (AS), such as inflammation, lipid metabolism, plaque stability, vascular smooth muscle cells (VSMCs) proliferation and endothelial dysfunction. This review is designed to provide useful clues to further understanding roles of Sp1 in the pathogenesis of AS, and may be helpful for the design of novel efficacious therapeutics agents targeting Sp1.

Activation of LXRα improves cardiac remodeling induced by pulmonary artery hypertension in rats

Inflammatory factors regulated by NF-κB play a significant role in PAH and myocardial hypertrophy. LXR activation may inhibit myocardial hypertrophy via suppressing inflammatory pathways; it is unknown whether LXR is also involved in PAH-induced myocardial hypertrophy or remodeling. To further explore the protective effect of LXR in PAH-induced cardiac hypertrophy and remodeling, a PAH model was developed, and T0901317, an agonist of LXR, was used to examine the effect of LXR activation. PAH rats demonstrated obvious cardiac hypertrophy and remodeling in the right ventricle, but significant improvement of cardiac hypertrophy and remodeling was observed in PAH rats treated with T0901317. Through RT-PCR, Western blot and ELISA examination, NF-κB, IL-6, TNF-α, and iNOS were found to be significantly reduced in PAH rats treated with T0901317 compared to PAH rats treated with DMSO. Apoptosis was also significantly reduced in PAH rats treated with T0901317. Thus, LXR activation may inhibit PAH-induced cardiac hypertrophy and remodeling by inhibiting NF-κB-mediated inflammatory pathways.

Curcumin Exerts its Anti-hypertensive Effect by Down-regulating the AT1 Receptor in Vascular Smooth Muscle Cells

Curcumin exerts beneficial effects on cardiovascular diseases, including hypertension. However, its mechanisms are unknown. We propose that curcumin prevents the development of hypertension by regulating AT₁ receptor (AT₁R) expression in arteries. The present study examined how curcumin regulates AT₁R expression in vascular smooth muscle cells and investigated the physiological significance of this regulation in angiotensin (Ang) II-induced hypertension. The results showed that curcumin decreased AT₁R expression in a concentration- and time-dependent manner in vascular smooth muscle cells. Using luciferase reporters with an entire AT₁ or a mutant AT₁R in A10 cells, the AT₁R promoter activity was inhibited by 10⁻⁶M curcumin, and the proximal element (from −61 to +25 bp) of the AT₁R promoter was crucial for curcumin-induced AT₁R down-regulation. An electrophoretic mobility shift assay showed that curcumin decreased specificity protein 1 (SP1) binding with the AT₁R promoter in A10 cells. Curcumin treatment reduced Ang II-induced hypertension in C57Bl/6J mice, which was accompanied by lower AT₁R expression in the arteries and decreased Ang II-mediated vasoconstriction in the mesenteric artery. These findings indicate that curcumin down-regulates AT₁R expression in A10 cells by affecting SP1/AT₁R DNA binding, thus reducing AT₁R-mediated vasoconstriction and subsequently prevents the development of hypertension in an Ang II-induced hypertensive model.

Emerging role of liver X receptors in cardiac pathophysiology and heart failure

Liver X receptors (LXRs) are master regulators of metabolism and have been studied for their pharmacological potential in vascular and metabolic disease. Besides their established role in metabolic homeostasis and disease, there is mounting evidence to suggest that LXRs may exert direct beneficial effects in the heart. Here, we aim to provide a conceptual framework to explain the broad mode of action of LXRs and how LXR signaling may be an important local and systemic target for the treatment of heart failure. We discuss the potential role of LXRs in systemic conditions associated with heart failure, such as hypertension, diabetes, and renal and vascular disease. Further, we expound on recent data that implicate a direct role for LXR activation in the heart, for its impact on cardiomyocyte damage and loss due to ischemia, and effects on cardiac hypertrophy, fibrosis, and myocardial metabolism. Taken together, the accumulating evidence supports the notion that LXRs may represent a novel therapeutic target for the treatment of heart failure.

MiR-320a contributes to atherogenesis by augmenting multiple risk factors and down-regulating SRF

Atherosclerosis progress is regulated by a variety of factors. Here, we show that miR-320a, an intergenic miRNA, is markedly elevated in the peripheral blood of coronary heart disease patients and high-risk patients. Microarray analysis and qRT-PCR assays showed that circulating miRNA-320a was highly expressed in coronary artery disease patients. In vivo study showed that overexpression of miR-320a resulted in significant increase in levels of plasma lipid (total cholesterol, Triglyceride and low-density lipoprotein) and serum inflammatory cytokines (IL-6, MCP-1, sICAM, pSelectin, TNF-α and fibrinogen). In ApoE(-/-) mice, miR-320a expression attenuates endothelium cell function and promotes atherogenesis. Bioinformatics analysis identified serum response factor as a potential target for miR-320a, which was validated by luciferase reporter activity assay and western-blot in vitro and in vivo. Moreover, miR-320a expression inhibits human-derived endothelium cell proliferation and induces apoptosis. We also found that SP1 transcriptionally up-regulates hsa-miR-320a expression. Our observations indicate that miR-320a is a key regulator contributing to multiple aspects of atherogenesis.

Bone marrow angiotensin AT2 receptor deficiency aggravates atherosclerosis development by eliminating macrophage liver X receptor-mediated anti-atherogenic actions

BACKGROUND

Bone marrow (BM) Angiotensin II (Ang II) type 1 (AT1) receptor plays a crucial role in atherosclerosis development; however, the effect of BM Ang II type 2 (AT2) receptor on atherogenesis remains undefined.

METHODS AND RESULTS

We generated BM chimera apoE-deficient (apoE(-/-)) mice whose BM cells were repopulated with AT2-deficient (Agtr2(-/-)) or wild-type (Agtr2(+/+)) cells. After 2 months of a high-cholesterol diet, the atherosclerotic lesion area was significantly increased in the apoE(-/-)/BM-Agtr2(-/-) mice compared with the apoE(-/-)/BM-Agtr2(+/+) mice (51%, P < 0.05), accompanied by an augmented accumulation of lesion macrophages. Although phenotypic polarization in BM-derived macrophages and lipopolysaccharide-induced expression of proinflammatory cytokines in thioglycollate-induced peritoneal macrophages (TGPMs) were not affected by AT2-deficiency, mRNA and protein expression levels of macrophage liver X receptor β (LXRβ) were significantly decreased in Agtr2(-/-) TGPMs compared with Agtr2(+/+) TGPMs. Anti-inflammatory effects of LXR agonist (GW3965) were markedly inhibited in Agtr2(-/-) TGPMs. Furthermore, the expression levels of ATP-binding cassette transporter ABCA1 and CCR7 were much lower in Agtr2(-/-) TGPMs than Agtr2(+/+) TGPMs, accompanied by a significantly reduced cholesterol efflux.

CONCLUSIONS

Our findings demonstrate that BM-AT2 deficiency aggravates atherosclerosis, at least in part, by eliminating the anti-atherogenic properties of macrophages elicited by LXRβ activation.

Activation of the retinoid X receptor modulates angiotensin II-induced smooth muscle gene expression and inflammation in vascular smooth muscle cells

The retinoid X receptor (RXR) partners with numerous nuclear receptors, such as the peroxisome proliferator activated receptor (PPAR) family, liver X receptors (LXRs), and farnesoid X receptor (FXR). Although each heterodimer can be activated by specific ligands, a subset of these receptors, defined as permissive nuclear receptors, can also be activated by RXR agonists known as rexinoids. Many individual RXR heterodimers have beneficial effects in vascular smooth muscle cells (SMCs). Because rexinoids can potently activate multiple RXR pathways, we hypothesized that treating SMCs with rexinoids would more effectively reverse the pathophysiologic effects of angiotensin II than an individual heterodimer agonist. Cultured rat aortic SMCs were pretreated with either an RXR agonist (bexarotene or 9-cis retinoic acid) or vehicle (dimethylsulfoxide) for 24 hours before stimulation with angiotensin II. Compared with dimethylsulfoxide, bexarotene blocked angiotensin II-induced SM contractile gene induction (calponin and smooth muscle-α-actin) and protein synthesis ([(3)H]leucine incorporation). Bexarotene also decreased angiotensin II-mediated inflammation, as measured by decreased expression of monocyte chemoattractant protein-1 (MCP-1). Activation of p38 mitogen-activated protein (MAP) kinase but not extracellular signal-related kinase (ERK) or protein kinase B (Akt) was also blunted by bexarotene. We compared bexarotene to five agonists of nuclear receptors (PPARα, PPARγ, PPARδ, LXR, and FXR). Bexarotene had a greater effect on calponin reduction, MCP-1 inhibition, and p38 MAP kinase inhibition than any individual agonist. PPARγ knockout cells demonstrated blunted responses to bexarotene, indicating that PPARγ is necessary for the effects of bexarotene. These data demonstrate that RXR is a potent modulator of angiotensin II-mediated responses in the vasculature, partially through inhibition of p38.

Lack of association between LXRα and LXRβ gene polymorphisms and prevalence of metabolic syndrome: a case-control study of an Iranian population

The metabolic syndrome (MetS) is considered to be a major risk factor for type 2 diabetes mellitus and cardiovascular diseases. It is characterized by central adiposity, high blood pressure, glucose intolerance and abnormalities of lipoprotein metabolism. The cause of MetS is likely to be due to a complex interaction between genetic and environmental factors. Liver X receptors alpha (NR1H3) and beta (NR1H2) play a key role in lipid and carbohydrate metabolism. The aim of this study was to investigate the contribution of genetic polymorphisms in the LXRs to risk of MetS and related traits. Two common SNPs in NR1H3 (rs11039155 and rs2279238) and in NR1H2 (rs17373080 and rs2695121) were genotyped using TaqMan assays in MetS patients (n=265) and controls (n=219). Logistic regression analyses were performed to calculate the odds ratios (ORs) as a measure of association of genotypes with the presence of MetS and related phenotypes. Although The NR1H2 polymorphism rs2695121 was nominally associated with MetS but correction for multiple-testing and adjustment for age, sex and number of MetS criteria, failed to identify any significant interactions associated with prevalence of MetS. However in the haplotype analysis, a LXRα haplotype AC, was more common in controls and was associated with a significant protective effect for MetS (OR [95% CI]=0.25 [0.07-0.88], p=0.031). In conclusion, this study suggests that the above-named variants in LXRα and LXRβ genes are not potential contributors to the risk of MetS and related traits in an Iranian population.

LXRβ/estrogen receptor-α signaling in lipid rafts preserves endothelial integrity

Liver X receptors (LXR) are stimulated by cholesterol-derived oxysterols and serve as transcription factors to regulate gene expression in response to alterations in cholesterol. In the present study, we investigated the role of LXRs in vascular endothelial cells (ECs) and discovered that LXRβ has nonnuclear function and stimulates EC migration by activating endothelial NOS (eNOS). This process is mediated by estrogen receptor-α (ERα). LXR activation promoted the direct binding of LXRβ to the ligand-binding domain of ERα and initiated an extranuclear signaling cascade that requires ERα Ser118 phosphorylation by PI3K/AKT. Further studies revealed that LXRβ and ERα are colocalized and functionally coupled in EC plasma membrane caveolae/lipid rafts. In isolated aortic rings, LXR activation of NOS caused relaxation, while in mice, LXR activation stimulated carotid artery reendothelialization via LXRβ- and ERα-dependent processes. These studies demonstrate that LXRβ has nonnuclear function in EC caveolae/lipid rafts that entails crosstalk with ERα, which promotes NO production and maintains endothelial monolayer integrity in vivo.

Nuclear Receptors in atherosclerosis: a superfamily with many 'Goodfellas'

Nuclear Receptors form a superfamily of 48 transcription factors that exhibit a plethora of functions in steroid hormone signaling, regulation of metabolism, circadian rhythm and cellular differentiation. In this review, we describe our current knowledge on the role of Nuclear Receptors in atherosclerosis, which is a multifactorial disease of the vessel wall. Various cell types are involved in this chronic inflammatory pathology in which multiple cellular processes and numerous genes are dysregulated. Systemic risk factors for atherosclerosis are among others adverse blood lipid profiles, enhanced circulating cytokine levels, as well as increased blood pressure. Since many Nuclear Receptors modulate lipid profiles or regulate blood pressure they indirectly affect atherosclerosis. In the present review, we focus on the functional involvement of Nuclear Receptors within the atherosclerotic vessel wall, more specifically on their modulation of cellular functions in endothelial cells, smooth muscle cells and macrophages. Collectively, this overview shows that most of the Nuclear Receptors are athero-protective in atherosclerotic lesions.

Liver X receptors, atherosclerosis and inflammation

Liver X receptors (LXRs) belong to the nuclear receptor superfamily of ligand-dependent transcription factors. LXRs are activated by oxysterols, metabolites of cholesterol, and therefore act as intracellular sensors of this lipid. There are two LXR genes (α and β) that display distinct tissue/cell expression profiles. LXRs interact with regulatory sequences in target genes as heterodimers with retinoid X receptor. Such direct targets of LXR actions include important genes implicated in the control of lipid homeostasis, particularly reverse cholesterol transport. In addition, LXRs attenuate the transcription of genes associated with the inflammatory response indirectly by transrepression. In this review, we describe recent evidence that both highlights the key roles of LXRs in atherosclerosis and inflammation and provides novel insights into the mechanisms underlying their actions. In addition, we discuss the major limitations of LXRs as therapeutic targets for the treatment of atherosclerosis and how these are being addressed.

Angiotensin II AT(2) receptor decreases AT(1) receptor expression and function via nitric oxide/cGMP/Sp1 in renal proximal tubule cells from Wistar-Kyoto rats

BACKGROUND

The renin-angiotensin (Ang) system controls blood pressure, in part, by regulating renal tubular sodium transport. In the kidney, activation of the angiotensin II type 1 (AT(1)) receptor increases renal sodium reabsorption, whereas the angiotensin II type 2 (AT(2)) receptor produces the opposite effect. We hypothesized that the AT(2) receptor regulates AT(1) receptor expression and function in the kidney.

METHODS AND RESULTS

In immortalized renal proximal tubule (RPT) cells from Wistar-Kyoto rats, CGP42112, an AT(2) receptor agonist, decreased AT(1) receptor mRNA and protein expression (P < 0.05), as assessed by reverse transcriptase-polymerase chain reaction and immunoblotting. The inhibitory effect of the AT(2) receptor on AT(1) receptor expression was blocked by the AT(2) receptor antagonist, PD123319 (10 (-6)mol/l), the nitric oxide synthase inhibitor N(w)-nitro-L-arginine methyl ester (10(-4) mol/l), or the nitric oxide-dependent soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo-[4,3-a] quinoxalin-1-one (10(-5) mol/l), indicating that both nitric oxide and cyclic guanosine monophosphate (cGMP) were involved in the signaling pathway. Furthermore, CGP42112 decreased Sp1 serine phosphorylation and reduced the binding of Sp1 to AT(1) receptor DNA. Stimulation with Ang II (10(-11) mol/l per 30 min) enhanced Na(+)-K(+)-ATPase activity in RPT cells, which was prevented by pretreatment with CGP42112 (10(-7) mol/l per 24 h) (P < 0.05). The above-mentioned results were confirmed in RPT cells from AT(2) receptor knockout mice; AT(1) receptor expression and Ang II-stimulated Na-K-ATPase activity were greater in these cells than in RPT cells from wild-type mice (P < 0.05). AT(1)/AT(2) receptors co-localized and co-immunoprecipitated in RPT cells; short-term CGP42112 (10 mol/l per 30 min) treatment increased AT(1)/AT(2) receptor co-immunoprecipitation (P < 0.05).

CONCLUSIONS

These results indicate that the renal AT(2) receptor, via nitric oxide/cGMP/Sp1 pathway, regulates AT(1 )receptor expression and function, which may be important in the regulation of sodium excretion and blood pressure.

Macrophage polarization by angiotensin II-type 1 receptor aggravates renal injury-acceleration of atherosclerosis

OBJECTIVE

Angiotensin II is a major determinant of atherosclerosis. Although macrophages are the most abundant cells in atherosclerotic plaques and express angiotensin II type 1 receptor (AT1), the pathophysiologic role of macrophage AT1 in atherogenesis remains uncertain. We examined the contribution of macrophage AT1 to accelerated atherosclerosis in an angiotensin II-responsive setting induced by uninephrectomy (UNx).

METHODS AND RESULTS

AT1(-/-) or AT1(+/+) marrow from apolipoprotein E deficient (apoE(-/-)) mice was transplanted into recipient apoE(-/-) mice with subsequent UNx or sham operation: apoE(-/-)/AT1(+/+)→apoE(-/-)+sham; apoE(-/-)/AT1(+/+) →apoE(-/-)+UNx; apoE(-/-)/AT1(-/-)→apoE(-/-)+sham; apoE(-/-)/AT1(-/-)→apoE(-/-)+UNx. No differences in body weight, blood pressure, lipid profile, and serum creatinine were observed between the 2 UNx groups. ApoE(-/-)/AT1(+/+) →apoE(-/-)+UNx had significantly more atherosclerosis (16907±21473 versus 116071±8180 μm(2), P<0.05). By contrast, loss of macrophage AT1 which reduced local AT1 expression, prevented any effect of UNx on atherosclerosis (77174±9947 versus 75714±11333 μm(2), P=NS). Although UNx did not affect total macrophage content in the atheroma, lesions in apoE(-/-)/AT1(-/-)→apoE(-/-)+UNx had fewer classically activated macrophage phenotype (M1) and more alternatively activated phenotype (M2). Further, UNx did not affect plaque necrosis or apoptosis in apoE(-/-)/AT1(-/-)→apoE(-/-) whereas it significantly increased both (by 2- and 6-fold, respectively) in apoE(-/-)/AT1(+/+) →apoE(-/-) mice. Instead, apoE(-/-)/AT1(-/-)→apoE(-/-) had 5-fold-increase in macrophage-associated apoptotic bodies, indicating enhanced efferocytosis. In vitro studies confirmed blunted susceptibility to apoptosis, especially in M2 macrophages, and a more efficient phagocytic function of AT1(-/-) macrophages versus AT1(+/+).

CONCLUSIONS

AT1 receptor of bone marrow-derived macrophages worsens the extent and complexity of renal injury-induced atherosclerosis by shifting the macrophage phenotype to more M1 and less M2 through mechanisms that include increased apoptosis and impaired efferocytosis.

Liver X receptor α gene polymorphisms and variable cardiovascular outcomes in patients treated with antihypertensive therapy: results from the INVEST-GENES study

BACKGROUND/AIMS

Liver X receptor-α (LXRA) is a nuclear receptor that regulates genes important in cholesterol homeostasis and inflammation. Several single nucleotide polymorphisms (SNPs) in the LXRA gene (NR1H3) have been earlier associated with metabolic phenotypes (dyslipidemia and elevated body mass index). Metabolic dysregulation is a major contributor to coronary disease; therefore, we assessed LXRA in International Verapamil Sustained Release SR Trandolapril Study Genetic Substudy (INVEST-GENES), a genetic-substudy of a large clinical trial in patients with hypertension and coronary artery disease.

METHODS

Seven tag SNPs in the LXRA gene region (NR1H3) were selected for study: rs11039149, rs12221497, rs2279238, rs7120118, rs326213, rs11039159, and rs10501321. One thousand fifty-nine patients were genotyped from the INVEST-GENES case-control set (verapamil-sustained release-based or atenolol-based treatment strategies) that comprised of 297 cases frequency matched (approximately 2.5:1) with that of event-free controls by sex and race. The primary outcome was defined as first occurrence of all-cause death, nonfatal myocardial infarction, or nonfatal stroke. Adjusted odds ratios (ORs) were calculated using logistic regression.

RESULTS

Three of the seven SNPs were associated with significant effects on the primary outcome in nonBlacks. The variant G allele of rs11039149 and the variant A allele of rs12221497 were associated with reduced risk of experiencing the primary outcome [OR: 0.62, confidence interval (CI): 0.45-0.85, P=0.003 and OR: 0.60, CI: 0.39-0.91, P=0.016, respectively]. The rs2279238 genotype was associated with a significant increase in risk for the primary outcome (OR: 1.42, CI: 1.03-1.95, P=0.03). Furthermore, there was a significant genotype-treatment strategy interaction for carriers of the variant T allele of rs2279238 (OR for verapamil-sustained release strategy compared with atenolol strategy: 2.86, CI: 1.50-5.46, P=0.0015). Diplotype analyses showed that the SNPs are rarely coinherited and support the directionally opposite effects of the SNPs on the primary outcome.

CONCLUSION

LXRA genotypes were associated with variable risk for cardiovascular outcomes and pharmacogenetic effect in INVEST-GENES. These novel findings suggest that LXRA is a genetic/pharmacogenetic target that should be further explored.

Liver x receptor signaling pathways and atherosclerosis

First discovered as orphan receptors, liver X receptors (LXRs) were subsequently identified as the nuclear receptor target of the cholesterol metabolites, oxysterols. There are 2 LXR receptors encoded by distinct genes: LXRalpha is most highly expressed in the liver, adipose, kidney, adrenal tissues, and macrophages and LXRbeta is ubiquitously expressed. Despite differential tissue distribution, these isoforms have 78% homology in their ligand-binding domain and appear to respond to the same endogenous ligands. Work over the past 10 years has shown that the LXR pathway regulates lipid metabolism and inflammation via both the induction and repression of target genes. Given the importance of cholesterol regulation and inflammation in the development of cardiovascular disease, it is not surprising that activation of the LXR pathway attenuates various mechanisms underlying atherosclerotic plaque development. In this brief review, we will discuss the impact of the LXR pathway on both cholesterol metabolism and atherosclerosis.

Activation of liver X receptor-alpha reduces activation of the renal and cardiac renin-angiotensin-aldosterone system

Liver X receptor (LXR)-alpha is a pivotal player in reverse cholesterol metabolism. Recently, LXR-alpha was implicated as an immediate regulator of renin expression in a cAMP-responsive manner. To determine whether long-term LXR-alpha activation affects activation of the renal and cardiac renin-angiotensin-aldosterone system (RAAS), we treated mice with T0901317 (T09, a specific synthetic LXR agonist) in combination with the RAAS inducer isoproterenol (ISO). LXR-alpha-deficient (LXR-alpha(-/-)) and wild-type (WT) C57Bl/6J mice were treated with ISO, T09 or both for 7 days. Low-dose ISO treatment, not associated with an increase in blood pressure, caused an increase in renal renin mRNA, renin protein and ACE protein in WT mice. WT mice treated with both ISO and T09 had decreased renal renin, ACE and AT(1)R mRNA expression compared with mice treated with ISO only. Cardiac ACE mRNA expression was also reduced in the hearts of WT mice treated with ISO and T09 compared with those treated with ISO alone. The transcriptional changes of renin, ACE and AT(1)R were mostly absent in mice deficient for LXR-alpha, suggesting that these effects are importantly conferred through LXR-alpha. In conclusion, LXR-alpha activation blunts ISO-induced increases in mRNA expression of renin, AT(1)R and ACE in the heart and kidney. These findings suggest a role for LXR-alpha in RAAS regulation.

Liver X receptors are negative regulators of cardiac hypertrophy via suppressing NF-kappaB signalling

AIMS

Nuclear factor-kappaB (NF-kappaB) plays a critical role in cell growth and inflammation during the progression of cardiac hypertrophy and heart failure. Several members of nuclear receptor superfamily, including liver X receptors (LXRalpha and LXRbeta), have been shown to suppress inflammatory responses, but little is known about their effects in cardiomyocytes.

METHODS AND RESULTS

We investigated LXR expression patterns in pressure overload-induced hypertrophic hearts and the hypertrophic growth of the LXRalpha-deficient hearts from mice (C57/B6) in response to pressure overload. The underlying mechanisms were also explored using cultured myocytes. We found that cardiac expression of LXRalpha was upregulated in pressure overload-induced left ventricular hypertrophy in mice. Transverse aorta coarctation-induced left ventricular hypertrophy was exacerbated in LXRalpha-null mice relative to control mice. A synthetic LXR ligand, T1317, suppressed cardiomyocyte hypertrophy in response to angiotensin II and lipopolysaccharide treatments. In addition, LXR activation suppressed NF-kappaB signalling and the expression of associated inflammatory factors. Overexpression of constitutively active LXRalpha and beta in cultured myocytes suppressed NF-kappaB activity.

CONCLUSION

LXRs are negative regulators of cardiac growth and inflammation via suppressing NF-kappaB signalling in cardiomyocytes. This should provide new insights into novel therapeutic targets for treating cardiac hypertrophy and heart failure.

Liver X Receptors as Therapeutic Targets for Managing Cholesterol: Implications for Atherosclerosis and Other Inflammatory Conditions

Atherosclerosis is a disease characterized by excess cholesterol and inflammation in the blood vessels. The liver X receptors (alpha and beta) are members of the nuclear hormone receptor family that are activated by endogenous cholesterol metabolites. These receptors are widely expressed with a tissue distribution that includes the liver, intestine and macrophage. Upon activation, these receptors have been shown to increase reverse cholesterol transport from the macrophage back to the liver to aid in the removal of excess cholesterol. More recently, they have also been shown to inhibit the inflammatory response in macrophages. These functions are accomplished through direct regulation of gene transcription. Herein, we will describe the key benefits and potential risks of targeting the LXRs for the treatment of atherosclerosis.