Nuclear Receptor Corepressor Research Articles

Nuclear receptor corepressor 1 controls regulatory T cell subset differentiation and effector function.

FOXP3+ regulatory T cells (Treg cells) are key for immune homeostasis. Here, we reveal that nuclear receptor corepressor 1 (NCOR1) controls naïve and effector Treg cell states. Upon NCOR1 deletion in T cells, effector Treg cell frequencies were elevated in mice and in in vitro-generated human Treg cells. NCOR1-deficient Treg cells failed to protect mice from severe weight loss and intestinal inflammation associated with CD4+ T cell transfer colitis, indicating impaired suppressive function. NCOR1 controls the transcriptional integrity of Treg cells, since effector gene signatures were already upregulated in naïve NCOR1-deficient Treg cells while effector NCOR1-deficient Treg cells failed to repress genes associated with naïve Treg cells. Moreover, genes related to cholesterol homeostasis including targets of liver X receptor (LXR) were dysregulated in NCOR1-deficient Treg cells. However, genetic ablation of LXRβ in T cells did not revert the effects of NCOR1 deficiency, indicating that NCOR1 controls naïve and effector Treg cell subset composition independent from its ability to repress LXRβ-induced gene expression. Thus, our study reveals that NCOR1 maintains naïve and effector Treg cell states via regulating their transcriptional integrity. We also reveal a critical role for this epigenetic regulator in supporting the suppressive functions of Treg cells in vivo.

8780 The Role of Nuclear Receptor Corepressors 1 and 2 on Intestinal Carbohydrate Transport in Mice

Abstract Disclosure: M.J. Ritter: None. I. Amano: None. A.H. van der Spek: None. H.E. Daniel: None. A.N. Hollenberg: None. The nuclear receptor corepressors NCoR1 and NCoR2 are two critical regulators of metabolism that are required for maintaining metabolic homeostasis. Both NCoR1 and NCoR2 (also known as the silencing mediator of retinoic acid and thyroid hormone receptors; SMRT) recruit histone deacetylase 3 (HDAC3) to their deacetylase domain (DAD) to repress nuclear receptor (NR) target gene expression. Interruption of the DAD of NCoR1 in mice leads to lower body weight, decreased whole-body fat mass, insulin sensitization with altered oscillatory patterns of key metabolic genes (1). On the other hand, total body knock-out (KO) of SMRT leads to weight gain, insulin resistance, and hepatic steatosis with an increase in hepatic lipogenesis (2). Previously, we showed that the KO of NCoR1 and SMRT in tandem from adult mice led rapidly to weight loss, hypoglycemia, hypothermia and was lethal. Reductions in intestinal carbohydrate transporters were seen, including sodium-glucose linked transporter-1 (SGLT1), glucose transporter 2 (GLUT2), and glucose transporter 5 (GLUT5) (3). Thus, we hypothesized that NCoR1 and SMRT play unique roles in regulating intestinal carbohydrate metabolism, in turn controlling metabolic parameters including body mass and glucose levels. We then generated a novel model to enable KO of NCoR1 and SMRT throughout intestinal epithelial cells (IECs) in adult mice using a tamoxifen inducible cre under control of the villin 1 promoter. Mice were injected with tamoxifen and body weight and glucose were monitored daily. This was followed by both oral and intraperitoneal glucose tolerance testing (GTT) and metabolic phenotyping. Preliminary data showed that NCoR1 and SMRT KO leads to sustained weight loss and hypoglycemia with 50% survivability. Metabolic phenotyping confirmed reduction in body mass without concomitant reduction in food intake. Oral GTT showed a blunted peak in response to glucose gavage compared to intraperitoneal administration. Gene expression analysis showed reduction in SGLT1, GLUT2, and GLUT5 in addition to changes in metabolic pathways associated with fatty acid metabolism. Here, we show that NCoR1 and SMRT are critical regulators of body mass and glucose in part via their actions on carbohydrate transporters in the intestine. With the global burden of metabolic diseases, including obesity and diabetes, ever-rising, NCoR1 and SMRT represent an overlooked but important area of study to better our understanding of disease processes and identify new targets for treatment. We next aim to determine the functional mechanism by which weight loss and hypoglycemia develop in addition to identifying molecular targets and pathways regulated by NCoR1 and SMRT in IECs.

Intestinal epithelial cell NCoR deficiency ameliorates obesity and metabolic syndrome

Nuclear receptor corepressor (NCoR1) interacts with various nuclear receptors and regulates the anabolism and catabolism of lipids. An imbalance in lipid/energy homeostasis is also an important factor in obesity and metabolic syndrome development. In this study, we found that the deletion of NCoR1 in intestinal epithelial cells (IECs) mainly activated the nuclear receptor PPARα and attenuated metabolic syndrome by stimulating thermogenesis. The increase in brown adipose tissue thermogenesis was mediated by gut-derived tricarboxylic acid cycle intermediate succinate, whose production was significantly enhanced by PPARα activation in the fed state. Additionally, NCoR1 deletion derepressed intestinal LXR, increased cholesterol excretion, and impaired duodenal lipid absorption by decreasing bile acid hydrophobicity, thereby reversing the possible negative effects of intestinal PPARα activation. Therefore, the simultaneous regulatory effect of intestinal NCoR1 on both lipid intake and energy expenditure strongly suggests that it is a promising target for developing metabolic syndrome treatment.

Nuclear receptor corepressor 1 levels differentially impact the intracellular dynamics of mutant thyroid hormone receptors associated with resistance to thyroid hormone syndrome

Thyroid hormone receptor α1 (TRα1) undergoes nucleocytoplasmic shuttling and mediates gene expression in response to thyroid hormone (T3). In Resistance to Thyroid Hormone Syndrome α (RTHα), certain TRα1 mutants have higher affinity for nuclear corepressor 1 (NCoR1) and may form stable complexes that are not released in the presence of T3. Here, we examined whether NCoR1 modulates intranuclear mobility and nuclear retention of TRα1 or RTHα-associated mutants in transfected human cells, as a way of analyzing critical structural components of TRα1 and to further explore the correlation between mutations in TRα1 and aberrant intracellular trafficking. We found no significant difference in intranuclear mobility, as measured by fluorescence recovery after photobleaching, between TRα1 and select RTHα mutants, irrespective of NCoR1 expression. Nuclear-to-cytoplasmic fluorescence ratios of RTHα mutants, however, varied from TRα1 when NCoR1 was overexpressed, with a significant increase in nuclear retention for A263V and a significant decrease for A263S and R384H. In NCoR1-knockout cells, nuclear retention of A263S, A263V, P389R, A382P, C392X, and F397fs406X was significantly decreased compared to control (wild-type) cells. Luciferase reporter gene transcription mediated by TRα1 was significantly repressed by both NCoR1 overexpression and NCoR1 knockout. Most RTHα mutants showed minimal induction regardless of NCoR1 levels, but T3-mediated transcriptional activity was decreased for R384C and F397fs406X when NCoR1 was overexpressed, and also decreased for N359Y in NCoR1-knockout cells. Our results suggest a complex interaction between NCoR1 and RTHα mutants characterized by aberrant intracellular localization patterns and transcriptional activity that potentially arise from variable repressor complex stability, and may provide insight into RTHα pathogenesis on a molecular and cellular level.

Nuclear Receptor Corepressors NCOR1 and SMRT Regulate Metabolism via Intestinal Regulation of Carbohydrate Transport.

Nuclear receptor action is mediated in part by the nuclear receptor corepressor 1 (NCOR1) and the silencing mediator of retinoic acid and thyroid hormone receptor (SMRT). NCOR1 and SMRT regulate metabolic pathways that govern body mass, insulin sensitivity, and energy expenditure, representing an understudied area in the realm of metabolic health and disease. Previously, we found that NCOR1 and SMRT are essential for maintaining metabolic homeostasis and their knockout (KO) leads to rapid weight loss and hypoglycemia, which is not survivable. Because of a potential defect in glucose absorption, we sought to determine the role of NCOR1 and SMRT specifically in intestinal epithelial cells (IECs). We used a postnatal strategy to disrupt NCOR1 and SMRT throughout IECs in adult mice. These mice were characterized metabolically and underwent metabolic phenotyping, body composition analysis, and glucose tolerance testing. Jejunal IECs were isolated and profiled by bulk RNA sequencing. We found that the postnatal KO of NCOR1 and SMRT from IECs leads to rapid weight loss and hypoglycemia with a significant reduction in survival. This was accompanied by alterations in glucose metabolism and activation of fatty acid oxidation in IECs. Metabolic phenotyping confirmed a reduction in body mass driven by a loss of body fat without altered food intake. This appeared to be mediated by a reduction of key intestinal carbohydrate transporters, including SGLT1, GLUT2, and GLUT5. Intestinal NCOR1 and SMRT act in tandem to regulate glucose levels and body weight. This in part may be mediated by regulation of intestinal carbohydrate transporters.

Nuclear receptor Rev-erbα alleviates intervertebral disc degeneration by recruiting NCoR-HDAC3 co-repressor and inhibiting NLRP3 inflammasome.

Intervertebral discs (IVDs) are rhythmic tissues that experience daily low-load recovery. Notably, aging and abnormal mechanical stress predispose IVDs to degeneration due to dysrhythmia-induced disordered metabolism. Meanwhile, Rev-erbα acts as a transcriptional repressor in maintaining biorhythms and homeostasis; however, its function in IVD homeostasis and degeneration remains unclear. This study assessed the relationship between low Rev-erbα expression levels and IVD degeneration. Rev-erbα deficiency accelerated needle puncture or aging-induced IVD degeneration, characterized by increased extracellular matrix (ECM) catabolism and nucleus pulposus (NP) cell apoptosis. Mechanistically, Rev-erbα knockdown in NP cells aggravated rhIL1β-induced NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome activation, exacerbating the imbalanced ECM and NP cell apoptosis. Meanwhile, blocking NLRP3 inflammasome activation mitigated Rev-erbα deficiency and needle puncture-induced IVD degeneration. Particularly, Rev-erbα mediated the transcriptional repression of the NLRP3 inflammasome via the ligand heme-binding of nuclear receptor co-repressor (NCoR) and histone deacetylase 3 (HDAC3) complex. Thus, the increased expression of Rev-erbα in NP cells following short-term rhIL1β treatment failed to inhibit NLRP3 transcription in vitro owing to heme depletion. Pharmacological activation of Rev-erbα in vivo and in vitro alleviated IVD degeneration by altering the NLRP3 inflammasome. Taken together, targeting Rev-erbα may be a potential therapeutic strategy for alleviating IVD degeneration and its related diseases.

Transcriptional regulation of macrophage inflammation in the heart failure with preserved ejection fraction

Abstract Funding Acknowledgements None. Introduction Heart failure with preserved ejection fraction (HFpEF) is a global public health problem with no effective treatment available. Pro-inflammatory cardiac macrophages are emerging as key determinants of adverse left ventricular remodeling; however, their role in HFpEF remains poorly understood. Mechanistically, the recruitment and activation of macrophages represent a key event in maladaptive myocardial remodeling in HFpEF patients. Evidence suggests that remodeling processes in HFpEF hearts are orchestrated and amplified by cardiac macrophages which regulate cardiomyocyte function, endothelial cell activation and fibroblast differentiation. Here we sought to determine the role of macrophage inflammation in experimental and human HFpEF. Methods Experiments were performed in rat cardiomyocytes (H9c2), human endothelial cells (HAECS), transgenic mice, and left ventricular (LV) myocardial samples from patients with HFpEF. H9c2 and HAECS treated with pro-inflammatory macrophage-like cells (RAW 264.7) conditional media in the presence or knockdown of a top-ranking activator of M1 type macrophages such as nuclear receptor corepressor 1 (NCOR1), were used to elucidate better the involvement of this gene in transcriptional regulation in vitro. The cardiac function of myeloid cell-specific NCOR1 knockout HFpEF mice undergoing a high-fat diet and L-NAME was investigated. LV myocardial samples were used to evaluate the pro-inflammatory activity of macrophages in human HFpEF tissues. Results Human and murine LV specimens showed upregulation of vascular adhesion molecules (ICAM1, ICAM2, E-selectin), recruitment of M1 macrophages to the myocardium, and decreased M2 macrophages. Notably, NCOR1 deletion in macrophages protected against diastolic dysfunction, exercise intolerance, and myocardial inflammation (TNF-a, IL6, IL-1b). Mechanistically, induction of metabolic stress by palmitic acid induced macrophage polarization, upregulation of NCOR1 and inflammatory genes in RAW cells. By contrast, Finally, NCOR1 depletion prevented pro-inflammatory transcriptional programs and secretion of TNF-a, IL6 and IL-1b in the macrophage secretome. Conclusion Targeting macrophage NCOR1 could represent a promising approach to blunt myocardial inflammation in HFpEF.

Nuclear receptor corepressors non-canonically drive glucocorticoid receptor-dependent activation of hepatic gluconeogenesis.

Nuclear receptor corepressors (NCoRs) function in multiprotein complexes containing histone deacetylase 3 (HDAC3) to alter transcriptional output primarily through repressive chromatin remodelling at target loci1-5. In the liver, loss of HDAC3 causes a marked hepatosteatosis largely because of de-repression of genes involved in lipid metabolism6,7; however, the individual roles and contribution of other complex members to hepatic and systemic metabolic regulation are unclear. Here we show that adult loss of both NCoR1 and NCoR2 (double knockout (KO)) in hepatocytes phenocopied the hepatomegalic fatty liver phenotype of HDAC3 KO. In addition, double KO livers exhibited a dramatic reduction in glycogen storage and gluconeogenic gene expression that was not observed with hepatic KO of individual NCoRs or HDAC3, resulting in profound fasting hypoglycaemia. This surprising HDAC3-independent activation function of NCoR1 and NCoR2 is due to an unexpected loss of chromatin accessibility on deletion of NCoRs that prevented glucocorticoid receptor binding and stimulatory effect on gluconeogenic genes. These studies reveal an unanticipated, non-canonical activation function of NCoRs that is required for metabolic health.

Abstract 6055: COOTO-Me (10e) acts as a molecular glue to target NCOR/HDAC3 degradation

Abstract Histone deacetylase 3 (HDAC3) is overexpressed in cancer cells and functions as transcription repression complex with nuclear receptor corepressor (NCOR) to inhibit gene transcription. The pan-HDAC inhibitors have been approved for T-cell lymphoma with evident side effects. The selective HDAC3 inhibitors needs to be developed. Proteolysis-targeting chimera (PROTAC) approach is taken to design HDAC3 degraders with unsolved bioavailability obstacle. We screened small molecules with HDAC3 degradation ability and found two small molecules derived from glycyrrhetinic acid, methyl 2-cyano-3-oxo-18β-olean-1,9(11), 12-trien-30-oate (COOTO, 10e) and methyl 2-cyano-3,12-dioxo-18β-olean-1,9(11)-dien-30-oate (CDODO-Me, 10d), selectively decreased HDAC3 protein with increased acetylation of Histone 3. We explored the mechanism of HDAC3 degradation and found that 10e interrupted the interaction of HDAC3 with NCOR and induced degradation of both HDAC3 and NCOR protein. Biotin labeled 10e shows binding to both HDAC3 and NCOR directly as well as to E3 ligases SIAH2 and ITCH. Mass spectrometry analysis profiling reveals covalent interactions of 10e with multiple cysteine sites of SIAH2 in the binding regions for NCOR and HDAC3. Silencing SIAH2 blocks degradation of HDAC3. N-Acetylcysteine and GSH block the binding of 10e to HDAC3, NCOR and SIAH2. In addition, 10e decreased the levels of c-FLIP protein and increased the levels of NOXA protein leading to apoptosis induction. These data suggest that 10e functions as a molecular glue to attract SIAH2 to HDAC3 and NCOR to cause degradation through covalent binding. Citation Format: Ping Gong, Min Huang, Xin Li, Haoling Wang, Samuel Waxman, Linxiang Zhao, Yongkui Jing. COOTO-Me (10e) acts as a molecular glue to target NCOR/HDAC3 degradation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6055.

Abstract 2091: Pharmacological inhibition of chaperone-mediated autophagy via NCoR1/RARα targeting is effective against non-small cell lung cancer

Abstract Dysregulation of autophagy, the lysosomal degradation of intracellular components, has been universally described in cancer. While activity of macroautophagy changes in a context-dependent manner in cancers, the upregulation of chaperone-mediated autophagy (CMA) is well-described in all solid tumors studied to date. Upregulated CMA directly contributes to both tumor growth and protection against anti-oncogenic interventions in cancers. Selective degradation of anti-oncogenic and pro-apoptotic proteins, such as mutant p53 and PUMA, misfolded proteins, and glycolytic enzymes by CMA allows for increased survival, reduced cell death, increased stress resistance, and enhancement of the Warburg effect in cancer cells, respectively. As such, inhibition of CMA is an attractive target for anti-cancer therapeutics, but the field currently lacks protein targets specific to CMA and selective CMA inhibitors. We have previously demonstrated the regulatory effect of retinoic acid receptor alpha (RARα) and its coregulator, nuclear receptor corepressor 1 (NCoR1), on CMA through transcriptional upregulation of the CMA effector proteins (Bourdenx et al. Cell 2021, Gomez-Sintes et al, Nat. Commun. 2022). Here, we identified a high NCoR1/RARα expression ratio in human non-small cell lung cancer (NSCLC) tumors compared to healthy lung tissue. We further illustrated a dependency on NCoR1 expression and its interaction with RARα to maintain high CMA activity in NSCLC cell lines. Provided the reliance on NCoR1 repression of RARα for high CMA activity in NSCLC, we hypothesized that small molecule targeting of the druggable NCoR1/RARα interaction to disrupt the interaction may result in suppression of CMA effector proteins and CMA inhibition. Through a series of in-silico screens for predicted NCoR1/RARα targeting, and functional screens for CMA inhibition, we identified CIM7, a first-in-class potent and selective CMA inhibitor. We validated CIM7 function through binding to RARα and subsequent disruption of NCoR1 binding, resulting in alterations to CMA-related gene expression. CIM7 inhibits CMA in vivo with no observed toxicity in normal tissues. We additionally demonstrated the therapeutic potential of CIM7 through its ability to reduce tumor growth in vivo in mouse NSCLC xenografts. Our findings support the NCoR1/RARα interaction as a major regulator of CMA in NSCLC and demonstrate the potential of pharmacologic CMA inhibition as an anti-cancer therapeutic strategy. Citation Format: Mericka McCabe, Rabia R. Khawaja, Rajanya Bhattacharyya, Antonio Diaz, Thomas P. Garner, Kristen Lindenau, Rebecca Sereda, Olaya Santiago-Fernández, Ana Maria Cuervo, Evripidis Gavathiotis. Pharmacological inhibition of chaperone-mediated autophagy via NCoR1/RARα targeting is effective against non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2091.

Targeting nuclear receptor corepressors for reversible male contraception

Despite numerous female contraceptive options, nearly half of all pregnancies are unintended. Family planning choices for men are currently limited to unreliable condoms and invasive vasectomies with questionable reversibility. Here, we report the development of an oral contraceptive approach based on transcriptional disruption of cyclical gene expression patterns during spermatogenesis. Spermatogenesis involves a continuous series of self-renewal and differentiation programs of spermatogonial stem cells (SSCs) that is regulated by retinoic acid (RA)-dependent activation of receptors (RARs), which control target gene expression through association with corepressor proteins. We have found that the interaction between RAR and the corepressor silencing mediator of retinoid and thyroid hormone receptors (SMRT) is essential for spermatogenesis. In a genetically engineered mouse model that negates SMRT-RAR binding (SMRTmRID mice), the synchronized, cyclic expression of RAR-dependent genes along the seminiferous tubules is disrupted. Notably, the presence of an RA-resistant SSC population that survives RAR de-repression suggests that the infertility attributed to the loss of SMRT-mediated repression is reversible. Supporting this notion, we show that inhibiting the action of the SMRT complex with chronic, low-dose oral administration of a histone deacetylase inhibitor reversibly blocks spermatogenesis and fertility without affecting libido. This demonstration validates pharmacologic targeting of the SMRT repressor complex for non-hormonal male contraception.

Vitamin D inhibits tamoxifen-induced non-alcoholic fatty liver disease through a nonclassical estrogen receptor/liver X receptor pathway

Non-alcoholic Fatty Liver Disease (NAFLD) is one of the common side effects of tamoxifen treatment for estrogen receptor-positive breast cancer, and is representative of disorders of energy metabolism. Fatty liver is induced after tamoxifen (TAM) inhibition of estrogen receptor activity, but the exact mechanism is not clear. This study investigated the effects and mechanisms of TAM-induced steatosis in the liver. The effects and mechanisms of TAM on hepatocyte lipid metabolism were assessed using C57BL/6 female mice and human hepatoma cells. TAM promoted fat accumulation in the liver by upregulation of Srebp-1c expression. Regarding the molecular mechanism, TAM promoted the recruitment of the auxiliary transcriptional activator, p300, and dissociated the auxiliary transcriptional repressor, nuclear receptor corepressor (NCOR), of the complexes, which led to enhancement of Srebp-1c transcription and an increase of triglyceride (TG) synthesis. Vitamin D (VD), a common fat-soluble vitamin, can decrease TAM-induced NAFLD by promoting p300 dissociation and NCOR recruitment. Tamoxifen promoted the recruitment and dissociation of co-transcription factors on the LXR/ER/RXR receptor complex, leading to a disorder of liver lipid metabolism. VD interfered with TAM-induced liver lipid metabolism disorders by reversing this process.

A TLR4/TRAF6-dependent signaling pathway mediates NCoR coactivator complex formation for inflammatory gene activation.

The nuclear receptor corepressor (NCoR) forms a complex with histone deacetylase 3 (HDAC3) that mediates repressive functions of unliganded nuclear receptors and other transcriptional repressors by deacetylation of histone substrates. Recent studies provide evidence that NCoR/HDAC3 complexes can also exert coactivator functions in brown adipocytes by deacetylating and activating PPARγ coactivator 1α (PGC1α) and that signaling via receptor activator of nuclear factor kappa-B (RANK) promotes the formation of a stable NCoR/HDAC3/PGC1β complex that coactivates nuclear factor kappa-B (NFκB)- and activator protein 1 (AP-1)-dependent genes required for osteoclast differentiation. Here, we demonstrate that activation of Toll-like receptor (TLR) 4, but not TLR3, the interleukin 4 (IL4) receptor nor the Type I interferon receptor, also promotes assembly of an NCoR/HDAC3/PGC1β coactivator complex. Receptor-specific utilization of TNF receptor-associated factor 6 (TRAF6) and downstream activation of extracellular signal-regulated kinase 1 (ERK1) and TANK-binding kinase 1 (TBK1) accounts for the common ability of RANK and TLR4 to drive assembly of an NCoR/HDAC3/PGC1β complex in macrophages. ERK1, the p65 component of NFκB, and the p300 histone acetyltransferase (HAT) are also components of the induced complex and are associated with local histone acetylation and transcriptional activation of TLR4-dependent enhancers and promoters. These observations identify a TLR4/TRAF6-dependent signaling pathway that converts NCoR from a corepressor of nuclear receptors to a coactivator of NFκB and AP-1 that may be relevant to functions of NCoR in other developmental and homeostatic processes.

The thyroid hormone enhances mouse embryonic fibroblasts reprogramming to pluripotent stem cells: role of the nuclear receptor corepressor 1.

Pluripotent stem cells can be generated from somatic cells by the Yamanaka factors Oct4, Sox2, Klf4 and c-Myc. Mouse embryonic fibroblasts (MEFs) were transduced with the Yamanaka factors and generation of induced pluripotent stem cells (iPSCs) was assessed by formation of alkaline phosphatase positive colonies, pluripotency gene expression and embryod bodies formation. The thyroid hormone triiodothyronine (T3) enhances MEFs reprogramming. T3-induced iPSCs resemble embryonic stem cells in terms of the expression profile and DNA methylation pattern of pluripotency genes, and of their potential for embryod body formation and differentiation into the three major germ layers. T3 induces reprogramming even though it increases expression of the cyclin kinase inhibitors p21 and p27, which are known to oppose acquisition of pluripotency. The actions of T3 on reprogramming are mainly mediated by the thyroid hormone receptor beta and T3 can enhance iPSC generation in the absence of c-Myc. The hormone cannot replace Oct4 on reprogramming, but in the presence of T3 is possible to obtain iPSCs, although with low efficiency, without exogenous Klf4. Furthermore, depletion of the corepressor NCoR (or Nuclear Receptor Corepressor 1) reduces MEFs reprogramming in the absence of the hormone and strongly decreases iPSC generation by T3 and also by 9cis-retinoic acid, a well-known inducer of reprogramming. NCoR depletion also markedly antagonizes induction of pluripotency gene expression by both ligands. Inclusion of T3 on reprogramming strategies has a potential use in enhancing the generation of functional iPSCs for studies of cell plasticity, disease and regenerative medicine.

Nuclear receptor corepressor 1 deficiency exacerbates asthma by modulating macrophage polarization

Macrophage polarization plays an important role in asthma. Nuclear receptor corepressor 1 (NCOR1) plays an important role in metabolic and cardiovascular diseases by regulating the function of macrophages. The aim of this research was to examine the role and mechanism of macrophage NCOR1 in the development of asthma. We used ovalbumin (OVA) to induce macrophage NCOR1-deficient mice for asthma formation. Our results revealed that macrophage NCOR1 deficiency markedly enhanced allergic airway inflammation. In addition, NCOR1 deficiency in macrophages was found to enhance M2 polarization. Mechanistic studies suggested that NCOR1 promoted macrophage polarization by interacting with PPARγ, contributing to the pathogenesis of asthma. In conclusion, macrophage NCOR1 deficiency promoted the regulation of M2 programming by enhancing PPARγ expression to exacerbate asthma. Macrophage NCOR1 might be a potential target for the treatment of asthma.

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.

Early divergent responses to virulent and attenuated vaccine isolates of Flavobacterium covae sp. nov. In channel catfish, Ictalurus punctatus

Columnaris disease continues to inflict substantial losses among freshwater cultured species since its first description one hundred years ago. The experimental and anecdotal evidence suggests an expanded range and rising virulence of columnaris worldwide due to the warming global climate. The channel catfish (Ictalurus punctatus) are particularly vulnerable to columnaris. A recently developed live attenuated vaccine (17–23) for Flavobacterium columnare (now Flavobacterium covae sp. nov.) demonstrated superior protection for vaccinated catfish against genetically diverse columnaris isolates. In this study, we aimed to elucidate the molecular mechanisms and patterns of immune evasion and host manipulation linked to virulence by comparing gene expression changes in the host after the challenge with a virulent (BGSF-27) or live attenuated F. covae sp. nov. vaccine (17–23). Thirty-day-old fry were accordingly challenged with either virulent or vaccine isolates. Gill tissues were collected at 0 h (control), 1 h, and 2 h post-infection, which are two critical time points in early host-pathogen interactions. Transcriptome profiling of the gill tissues revealed a larger number (518) of differentially expressed genes (DEGs) in vaccine-exposed fish than those exposed to the virulent pathogen (321). Pathway analyses suggested potent suppression of early host immune responses by the virulent isolate through a higher expression of nuclear receptor corepressors (NCoR) responsible for antagonizing macrophage and T-cell signaling. Conversely, in vaccinated fry, we observed induction of Ca2+/calmodulin-dependent protein kinase II (CAMKII), responsible for clearing NCoR, and commensurate up-regulation of transcription factor AP-1 subunits, c-Fos, and c-Jun. As in mammalian systems, AP-1 expression was connected with a broad immune activation in vaccinated fry, including induction of CC chemokines, proteinases, iNOS, and IL-12b. Relatedly, divergent expression patterns of Src tyrosine kinase Lck, CD44, and CD28 indicated a delay or suppression of T-cell adhesion and activation in fry exposed to the virulent isolate. Broader implications of these findings will be discussed. The transcriptomic differences between virulent and attenuated bacteria may offer insights into how the host responds to the vaccination or infection and provide valuable knowledge to understand the early immune mechanisms of columnaris disease in aquaculture.

Genetic Deletion of Hepatic NCOR1 regulates the bile acid metabolism and leads to reduction in atherosclerosis

Abstract 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. Since NCOR1 transrepresses the function of several nuclear receptors involved in hepatic lipid transport and synthesis, we hypothesized that genetic NCOR1 deletion in the liver alters lipid metabolism and atherosclerosis development. Methods To test this hypothesis, we generated hepatocyte-specific Ncor1 knockout mice on a Ldlr-/- background. Besides assessing the progression of the disease in thoraco-abdominal aortae en face, we analyzed hepatic cholesterol and bile acid metabolism at expression and functional level. Results This study findings demonstrated that 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, hepatic cholesterol and triglyceride contents were 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. Hepatocyte NCOR1 may therefore provide a novel target for development of anti-atherosclerotic drugs.

An intrinsically disordered region controlling condensation of a circadian clock component and rhythmic transcription in the liver

Circadian gene transcription is fundamental to metabolic physiology. Here we report that the nuclear receptor REV-ERBα, a repressive component of the molecular clock, forms circadian condensates in the nuclei of mouse liver. These condensates are dictated by an intrinsically disordered region (IDR) located in the protein's hinge region which specifically concentrates nuclear receptor corepressor 1 (NCOR1) at the genome. IDR deletion diminishes the recruitment of NCOR1 and disrupts rhythmic gene transcription invivo. REV-ERBα condensates are located at high-order transcriptional repressive hubs in the liver genome that are highly correlated with circadian gene repression. Deletion of the IDR disrupts transcriptional repressive hubs and diminishes silencing of target genes by REV-ERBα. This work demonstrates physiological circadian protein condensates containing REV-ERBα whose IDR is required for hub formation and the control of rhythmic gene expression.

RANK ligand converts the NCoR/HDAC3 co-repressor to a PGC1β- and RNA-dependent co-activator of osteoclast gene expression

The nuclear receptor co-repressor (NCoR) complex mediates transcriptional repression dependent on histone deacetylation by histone deacetylase 3 (HDAC3) as a component of the complex. Unexpectedly, we found that signaling by the receptor activator of nuclear factor κB (RANK) converts the NCoR/HDAC3 co-repressor complex to a co-activator of AP-1 and NF-κB target genes that are required for mouse osteoclast differentiation. Accordingly, the dominant function of NCoR/HDAC3 complexes in response to RANK signaling is to activate, rather than repress, gene expression. Mechanistically, RANK signaling promotes RNA-dependent interaction of the transcriptional co-activator PGC1β with the NCoR/HDAC3 complex, resulting in the activation of PGC1β and inhibition of HDAC3 activity for acetylated histone H3. Non-coding RNAs Dancr and Rnu12, which are associated with altered human bone homeostasis, promote NCoR/HDAC3 complex assembly and are necessary for RANKL-induced osteoclast differentiation invitro. These findings may be prototypic for signal-dependent functions of NCoR in other biological contexts.