Role of the Nuclear Receptor Corepressor 1 (NCOR1) in Atherosclerosis and Associated Immunometabolic Diseases

The transcription factor PPARA mediates SIRT1 regulation of NCOR1 to protect damaged heart cells

Background

Heart failure (HF) is a clinical syndrome with a high risk. Our previous research showed a regulatory relationship between Sirtuin 1 (SIRT1), peroxisome proliferator-activated receptor α (PPARA) and nuclear receptor co-repressor 1 (NCOR1). This study aimed to investigate the regulatory mechanism of SIRT1/PPARA/NCOR1 axis in HF.

Methods

HF models in vitro were established by doxorubicin (DOX)-induced AC16 and human cardiac microvascular endothelial cell (HCMEC) lines. The contents of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), interleukin-1β (IL-1β), and IL-18 were detected using enzyme-linked immunosorbent assay. Then, we assessed the levels of reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD) and adenosine triphosphate (ATP). Moreover, the relationship between SIRT1 and PPARA was detected using the co-immunoprecipitation (Co-IP) analysis. The connection between PPARA and NCOR1 was analyzed using chromatin immunoprecipitation (ChIP).

Results

Overexpression of SIRT1 or PPARA could reduce apoptosis in DOX-induced AC16 and HCMEC cells, the levels of IL-1β, IL-18, ANP, BNP, ROS and MDA, while increasing the levels of SOD and ATP. In addition, overexpression of PPARA could increase the viability of DOX-induced cells and the levels of myosin heavy chain 6 (Myh6) and Myh7. Co-IP showed that SIRT1 interacted with PPARA. Silencing PPARA could reverse the effect of SIRT1 overexpression on DOX-induced AC16 and HCMEC cells. ChIP assay demonstrated that PPARA could bind to the promoter region of NCOR1. Silencing NCOR1 could reverse the effect of PPARA overexpression on DOX-induced AC16 and HCMEC cells.

Conclusions

This study revealed that PPARA could mediate SIRT1 to promote NCOR1 expression and thus protect damaged heart cells. The finding provided an important reference for the treatment of HF.

Impact of Ring Finger Protein 20 and Its Downstream Regulation on Renal Tubular Injury in a Unilateral Nephrectomy Mouse Model Fed a High-Fat Diet

Abnormal lipid metabolism increases the relative risk of kidney disease in patients with a single kidney. Using transcriptome analysis, we investigated whether a high-fat diet leads to abnormalities in lipid metabolism and induces kidney cell-specific damage in unilateral nephrectomy mice. Mice with unilateral nephrectomy fed a high-fat diet for 12 weeks exhibited progressive renal dysfunction in proximal tubules, including lipid accumulation, vacuolization, and cell damage. Ring finger protein 20 (RNF20) is a ligase of nuclear receptor corepressor of peroxisome proliferator-activated receptors (PPARs). The transcriptome analysis revealed the involvement of RNF20-related transcriptome changes in PPAR signaling, lipid metabolism, and water transmembrane transporter under a high-fat diet and unilateral nephrectomy. In vitro treatment of proximal tubular cells with palmitic acid induced lipotoxicity by altering RNF20, PPARα, and ATP-binding cassette subfamily A member 1 (ABCA1) expression. PPARγ and aquaporin 2 (AQP2) expression decreased in collecting duct cells, regulating genetic changes in the water reabsorption process. In conclusion, a high-fat diet induces lipid accumulation under unilateral nephrectomy via altering RNF20-mediated regulation and causing functional damage to cells as a result of abnormal lipid metabolism, thereby leading to structural and functional kidney deterioration.

Insights into the function of HDAC3 and NCoR1/NCoR2 co-repressor complex in metabolic diseases

Histone deacetylase 3 (HDAC3) and nuclear receptor co-repressor (NCoR1/2) are epigenetic regulators that play a key role in gene expression and metabolism. HDAC3 is a class I histone deacetylase that functions as a transcriptional co-repressor, modulating gene expression by removing acetyl groups from histones and non-histone proteins. NCoR1, on the other hand, is a transcriptional co-repressor that interacts with nuclear hormone receptors, including peroxisome proliferator-activated receptor gamma (PPARγ) and liver X receptor (LXR), to regulate metabolic gene expression. Recent research has revealed a functional link between HDAC3 and NCoR1 in the regulation of metabolic gene expression. Genetic deletion of HDAC3 in mouse models has been shown to improve glucose intolerance and insulin sensitivity in the liver, skeletal muscle, and adipose tissue. Similarly, genetic deletion of NCoR1 has improved insulin resistance and reduced adiposity in mouse models. Dysregulation of this interaction has been associated with the development of cardio-metabolic diseases such as cardiovascular diseases, obesity and type 2 diabetes, suggesting that targeting this pathway may hold promise for the development of novel therapeutic interventions. In this review, we summarize the current understanding of individual functions of HDAC3 and NCoR1/2 and the co-repressor complex formation (HDAC3/NCoR1/2) in different metabolic tissues. Further studies are needed to thoroughly understand the mechanisms through which HDAC3, and NCoR1/2 govern metabolic processes and the implications for treating metabolic diseases.

Genetic deletion of hepatic NCOR1 protects from atherosclerosis by promoting alternative bile acid-metabolism and sterol excretion

BACKGROUND

The nuclear receptor corepressor 1 (NCOR1) plays an important role in the regulation of gene expression in immunometabolic conditions by connecting chromatin-modifying enzymes, coregulators and transcription factors. NCOR1 has been shown to be involved in cardiometabolic diseases. Recently, we demonstrated that the deletion of macrophage NCOR1 aggravates atherosclerosis by promoting CD36-triggered foam cell formation via PPARG derepression.

PURPOSE

Since NCOR1 modulates the function of several key regulators involved in hepatic lipid and bile acid metabolism, we hypothesized that its deletion in hepatocytes alters lipid metabolism and atherogenesis.

METHODS

To test this hypothesis, we generated hepatocyte-specific Ncor1 knockout mice on a Ldlr-/- background. Besides assessing the progression of the disease in thoracoabdominal aortae en face, we analyzed hepatic cholesterol and bile acid metabolism at expression and functional levels.

RESULTS

Our data demonstrate that liver-specific Ncor1 knockout mice on an atherosclerosis-prone background develop less atherosclerotic lesions than controls. Interestingly, under chow diet, plasma cholesterol levels of liver-specific Ncor1 knockout mice were slightly higher compared to control, but strongly reduced compared to control mice after feeding them an atherogenic diet for 12 weeks. Moreover, the hepatic cholesterol content was decreased in liver-specific Ncor1 knockout compared to control mice. Our mechanistic data revealed that NCOR1 reprograms the synthesis of bile acids towards the alternative pathway, which in turn reduce bile hydrophobicity and enhances fecal cholesterol excretion.

CONCLUSIONS

Our data suggest that hepatic Ncor1 deletion in mice decreases atherosclerosis development by reprograming bile acid metabolism and enhancing fecal cholesterol excretion.

NCoR1 controls immune tolerance in conventional dendritic cells by fine-tuning glycolysis and fatty acid oxidation

Dendritic cells (DCs) undergo rapid metabolic reprogramming to generate signal-specific immune responses. The fine control of cellular metabolism underlying DC immune tolerance remains elusive. We have recently reported that NCoR1 ablation generates immune-tolerant DCs through enhanced IL-10, IL-27 and SOCS3 expression. In this study, we did comprehensive metabolic profiling of these tolerogenic DCs and identified that they meet their energy requirements through enhanced glycolysis and oxidative phosphorylation (OXPHOS), supported by fatty acid oxidation-driven oxygen consumption. In addition, the reduced pyruvate and glutamine oxidation with a broken TCA cycle maintains the tolerogenic state of the cells. Mechanistically, the AKT-mTOR-HIF-1α-axis mediated glycolysis and CPT1a-driven β-oxidation were enhanced in these tolerogenic DCs. To confirm these observations, we used synthetic metabolic inhibitors and found that the combined inhibition of HIF-1α and CPT1a using KC7F2 and etomoxir, respectively, compromised the overall transcriptional signature of immunological tolerance including the regulatory cytokines IL-10 and IL-27. Functionally, treatment of tolerogenic DCs with dual KC7F2 and etomoxir treatment perturbed the polarization of co-cultured naïve CD4⁺ T helper (Th) cells towards Th1 than Tregs, ex vivo and in vivo. Physiologically, the Mycobacterium tuberculosis (Mtb) infection model depicted significantly reduced bacterial burden in BMcDC1 ex vivo and in CD103⁺ lung DCs in Mtb infected NCoR1^DC-/-mice. The spleen of these infected animals also showed increased Th1-mediated responses in the inhibitor-treated group. These findings suggested strong involvement of NCoR1 in immune tolerance. Our validation in primary human monocyte-derived DCs (moDCs) showed diminished NCOR1 expression in dexamethasone-derived tolerogenic moDCs along with suppression of CD4⁺T cell proliferation and Th1 polarization. Furthermore, the combined KC7F2 and etomoxir treatment rescued the decreased T cell proliferative capacity and the Th1 phenotype. Overall, for the first time, we demonstrated here that NCoR1 mediated control of glycolysis and fatty acid oxidation fine-tunes immune tolerance versus inflammation balance in murine and human DCs.

LXR agonist inhibits inflammation through regulating MyD88 mRNA alternative splicing

Liver X receptors (LXRs) are important regulators of cholesterol metabolism and inflammatory responses. LXR agonists exhibit potently anti-inflammatory effects in macrophages, which make them beneficial to anti-atherogenic therapy. In addition to transrepressive regulation by SUMOylation, LXRs can inhibit inflammation by various mechanisms through affecting multiple targets. In this study, we found that the classic LXR agonist T0901317 mediated numerous genes containing alternative splice sites, including myeloid differentiation factor 88 (MyD88), that contribute to inflammatory inhibition in RAW264.7 macrophages. Furthermore, T0901317 increased level of alternative splice short form of MyD88 mRNA by down-regulating expression of splicing factor SF3A1, leading to nuclear factor κB-mediated inhibition of inflammation. In conclusion, our results suggest for the first time that the LXR agonist T0901317 inhibits lipopolysaccharide-induced inflammation through regulating MyD88 mRNA alternative splicing involved in TLR4 signaling pathway.

The Role of Transcription Factor PPAR-γ in the Pathogenesis of Psoriasis, Skin Cells, and Immune Cells

The peroxisome proliferator-activated receptor PPAR-γ is one of three PPAR nuclear receptors that act as ligand-activated transcription factors. In immune cells, the skin, and other organs, PPAR-γ regulates lipid, glucose, and amino acid metabolism. The receptor translates nutritional, pharmacological, and metabolic stimuli into the changes in gene expression. The activation of PPAR-γ promotes cell differentiation, reduces the proliferation rate, and modulates the immune response. In the skin, PPARs also contribute to the functioning of the skin barrier. Since we know that the route from identification to the registration of drugs is long and expensive, PPAR-γ agonists already approved for other diseases may also represent a high interest for psoriasis. In this review, we discuss the role of PPAR-γ in the activation, differentiation, and proliferation of skin and immune cells affected by psoriasis and in contributing to the pathogenesis of the disease. We also evaluate whether the agonists of PPAR-γ may become one of the therapeutic options to suppress the inflammatory response in lesional psoriatic skin and decrease the influence of comorbidities associated with psoriasis.

KLF7 Alleviates Atherosclerotic Lesions and Inhibits Glucose Metabolic Reprogramming in Macrophages by Regulating HDAC4/miR-148b-3p/NCOR1

OBJECTIVES

Atherosclerosis (AS) remains a major contributor to death worldwide. This study sought to explore the role of Krüppel-like factor 7 (KLF7) in AS lesions via regulating glucose metabolic reprogramming (GMR) in macrophages.

METHODS

AS mouse and cell models were established via high-fat-diet feeding and oxidized low-density lipoprotein (ox-LDL) induction. KLF7, histone deacetylase 4 (HDAC4), miR-148b-3p, and nuclear receptor corepressor 1 (NCOR1) expressions in aortic tissue and cells were detected via reverse transcription quantitative polymerase chain reaction or Western blotting. Parameters of AS lesions and mouse metabolism were detected via hematoxylin-eosin, oil red O, and Masson staining, assay kits, glucose tolerance test, and enzymatic analysis. Peritoneal macrophages of mice were isolated and cellular metabolism was detected via Seahorse metabolic flux analysis, assay kits, ELISA, and Western blotting. Bindings among KLF7, HDAC4, microRNA (miR)-148b-3p, and NCOR1 were testified via the dual-luciferase assay and chromatin immunoprecipitation assay.

RESULTS

KLF7 was poorly expressed in AS mice and ox-LDL-induced RAW264.7 cells. KLF7 overexpression attenuated AS lesions and rescued metabolic abnormities in AS mice, and reduced glucose intake and GMR in ox-LDL-induced RAW264.7 cells. Mechanically, KLF7 bound to the HDAC4 promoter to activate HDAC4. HDAC4 reduced H3 and H4 acetylation levels in the miR-148b promoter to inhibit miR-148b-3p and promote NCOR1 transcription. HDAC4 downregulation abolished the protective role of KLF7 overexpression in AS mice and ox-LDL-induced RAW264.7 cells via the miR-148b-3p/NCOR1 axis.

CONCLUSION

KLF7 bound to the HDAC4 promoter to activate HDAC4, inhibit miR-148b-3p via reducing acetylation level, and promote NCOR1 transcription, thereby limiting GMR in macrophages and alleviating AS lesions.