New insights into the suppression of inflammation and lipid accumulation by JAZF1

Abstract

Atherosclerosis is one of the leading causes of disease and death worldwide. The identification of new therapeutic targets and agents is critical. JAZF1 is expressed in many tissues and is found at particularly high levels in adipose tissue (AT). JAZF1 suppresses inflammation (including IL-1β, IL-4, IL-6, IL-8, IL-10, TNFα, IFN-γ, IAR-20, COL3A1, laminin, and MCP-1) by reducing NF-κB pathway activation and AT immune cell infiltration. JAZF1 reduces lipid accumulation by regulating the liver X receptor response element (LXRE) of the SREBP-1c promoter, the cAMP-response element (CRE) of HMGCR, and the TR4 axis. LXRE and CRE sites are present in many cytokine and lipid metabolism gene promoters, which suggests that JAZF1 regulates these genes through these sites. NF-κB is the center of the JAZF1-mediated inhibition of the inflammatory response. JAZF1 suppresses NF-κB expression by suppressing TAK1 expression. Interestingly, TAK1 inhibition also decreases lipid accumulation. A dual-targeting strategy of NF-κB and TAK1 could inhibit both inflammation and lipid accumulation. Dual-target compounds (including prodrugs) 1–5 exhibit nanomolar inhibition by targeting NF-κB and TAK1, EGFR, or COX-2. However, the NF-κB suppressing activity of these compounds is relatively low (IC₅₀ > 300 nM). Compounds 6–14 suppress NF-κB expression with IC₅₀ values ranging from 1.8 nM to 38.6 nM. HS-276 is a highly selective, orally bioavailable TAK1 inhibitor. Combined structural modifications of compounds using a prodrug strategy may enhance NF-κB inhibition. This review focused on the role and mechanism of JAZF1 in inflammation and lipid accumulation for the identification of new anti-atherosclerotic targets.

Introduction

Atherosclerosis is a common risk factor for the occurrence and development of many diseases, such as coronary heart disease (CHD), and a key problem threatening the health and life expectancy of the elderly population.^1,2 Atherosclerosis, which is characterized by the formation of fat-laden plaques in large and medium-sized vessels, has been identified as a chronic inflammatory disease of the artery wall. Atherosclerosis occurs during foam cell generation. Oxidative stress and intracellular reactive oxygen species (ROS) production cause vascular aging and induce LDL to oxidize and form ox-LDL. Previous studies from our laboratory and others have demonstrated that the uncontrolled uptake of ox-LDL by lectin-like oxidized low-density-lipoprotein receptor-1 (LOX-1), class A1 scavenger receptor (SR-A1), and cluster of differentiation 36 (CD36), and the impaired cholesterol efflux by ATP-binding cassette transporter A1 (ABCA1) and ABCG1 result in cholesterol accumulation and subsequently trigger macrophages and VSMCs to become foam cells.3, 4, 5, 6, 7 Lipid accumulation in macrophages could induce NLRP3 inflammasome activation. Ox-LDL could activate the NLRP3 inflammasomes (IL-1β and IL-18) in atherosclerosis by binding to the CD36–TLR4–TLR6 signaling complex. Ox-LDL also triggers inflammatory responses, such as interleukin-6 (IL-6), IL-7, IL-1β, and IL-15, to accelerate atherosclerosis development.⁸ Therefore, controlling lipid metabolism dysfunction and the inflammatory response is an essential measure for preventing atherosclerosis.

Juxtaposed with another zinc finger gene 1 (JAZF1, also named Tip27 and ZNF802) is a cysteine–histidine structured zinc finger protein. This gene encodes a 27-kDa nuclear protein containing 3 putative zinc finger motifs. JAZF1 is the corepressor of orphan nuclear receptor TR4 (also named NR2C2), which is a member of the nuclear orphan receptor family. Recent studies have demonstrated that JAZF1 plays an important role in atherosclerosis progression.⁹ To our knowledge, JAZF1 is expressed in a variety of tissues in humans and mice and is most highly expressed in adipose tissue (AT).¹⁰ However, JAZF1 is a relatively new gene with many unknown functions and mechanisms. The main aims of this review are to describe the role and mechanism of JAZF1 in immune and inflammatory responses and lipid metabolism and to discuss its contributions to atherosclerosis and its potential role in atherosclerosis treatment.

Role of JAZF1 in atherosclerosis

Many studies have shown that JAZF1 is associated with atherosclerosis. JAZF1 is downregulated in atherosclerosis development in prediabetes patients.¹¹ The rs864745 single nucleotide polymorphism (SNP) of JAZF1 is associated with atherosclerosis, which suggests that JAZF1 may be a potential biomarker.¹² Indeed, JAZF1 has been patented by several companies and scientists as a biomarker for a variety of diseases, including atherosclerosis (US20190078093A1 and WO2015073531A1), diabetes (EP2215266B1 and US20160138103A1), aging (US20140079836A1), lupus (JP2016095330A), and cancer (US20140357516A1, US20180045727A1, and EP3179393B1). In addition, JAZF1 also suppresses atherosclerosis development. The downregulation of JAZF1 expression leads to dysfunction in lipid metabolism and the inflammatory response.^13,14 JAZF1 overexpression by an adenoviral plasmid containing JAZF1 reduces the entire aorta's en face plaque area and the aortic sinus's cross-sectional plaque area in apoE^−/− mice by increasing JAZF1 expression in various tissues, including the liver and AT. JAZF1 reduces the blood TC (29%) and LDL-C (30%) levels and the hepatic TC levels (65%) in apoE^−/− mice. However, JAZF1 does not change the TG levels in the blood or hepatic tissue in apoE^−/− mice, which suggests that JAZF1 mainly regulates cholesterol metabolism.¹⁵ JAZF1 overexpression in transgenic JAZF1 mice also reduces the risk of atherosclerosis by increasing JAZF1 expression in various tissues, including the heart, liver, lung, testis, spleen, kidney, and pancreas.¹⁶ These transgenic mice show low inflammatory reaction, body weight, and abdominal fat, low levels of plasma parameters (including TG, TC, LDL-C, glucose, FBG, ALT, and AST), and low hepatic lipid accumulation (TG and TC).^13,14 However, these mice also exhibit heart failure symptoms (such as high blood pressure, cardiomyocyte apoptosis, absence of ventricular contractions, and mitochondrial defects) and enhanced expression of proapoptotic genes, including caspase-8/9, Bim, Apaf1, and Aifm1, which suggests that JAZF1 overexpression may have many side effects.¹⁶

Many studies have shown that aging, hepatic steatosis, obesity, and type 2 diabetes mellitus (T2DM) are risk factors for atherosclerosis.^17,18 The expression of JAZF1 is gradually downregulated in aging mice. JAZF1 overexpression steadily decreases the serum TG, TC, and LDL-C levels in aging mice.¹⁶ JAZF1 ameliorates aging and hepatic steatosis. The role of JAZF1 in obesity and T2DM has been reviewed.¹⁹ Overall, JAZF1 inhibits atherosclerosis development by suppressing the inflammatory response and lipid metabolism dysfunction.

New insights into the mechanism of JAZF1 in suppressing inflammation and lipid accumulation

Systemic immune and inflammatory responses of JAZF1 involving reducing NF-κB expression

The inflammatory response could induce atherosclerosis. JAZF1 reduces the levels of the inflammatory markers, including IL-4, IL-6, IL-10, interferon γ (IFN-γ), tumor necrosis factor-α (TNFα), fibrotic gene collagen type III alpha 1 (COL3A1) and Lamin, in mice.¹³ JAZF1 decreases the inflammatory state under high-fat diet (HFD) conditions. JAZF1 inhibits the expression of proinflammatory cytokines (such as TNFα, MCP-1, IAR-20, and IL-8) by reducing the NF-κB pathway in vitro and in vivo.^14,20,21 Thus, the NF-κB pathway plays key roles in suppressing the inflammatory response mediated by JAZF1.

Immune responses also regulate atherosclerosis development.²² JAZF1 suppresses chronic inflammation by inhibiting mouse peritoneal macrophage differentiation toward the CD11c⁺ M phenotype. In addition, JAZF1 suppresses chronic inflammation by increasing the number of Tregs and restrictive T cells and the secretion of IL-10 and IL-4. JAZF1 also reduces the number of CD4⁺ T cells, active T cells, and memory T cells and the secretion of IL-1β, TNF-α, and IL-6 in mice.23, 24, 25 Overall, JAZF1 suppresses atherosclerosis development by regulating immune and inflammatory responses and cytokines (including IL-1β, IL-4, IL-6, IL-8, IL-10, TNFα, IFN-γ, IAR-20, COL3A1, laminin, MCP-1, CD4⁺ T cells, active T cells, memory T cells, CD11c⁺ macrophages, and CD206⁺ macrophages) by reducing the activation of the NF-κB pathway.

Interestingly, the JAZF1-induced reduction in gene expression depends on the LXR-responsive element (LXRE) and the cAMP-response element (CRE) site in the gene promoter.¹³ The promoter of IFN-γ contains LXRE and CRE sites,^26,27 which suggests that JAZF1 reduces IFN-γ expression by regulating LXRE and CRE in the IFN-γ promoter. The promoters of many cytokines, including IL-1β,²⁸ IL-4,²⁹ IL-6,³⁰ IL-8,³¹ IL-10,³² TNFα,³³ and IL-17,^34,35, contain a CRE site, which suggests that JAZF1 reduces the expression of these cytokines by regulating the CRE in the promoters of the genes encoding these cytokines (Fig. 1).

Figure 1.

Role of AT macrophages, T cells, and their markers or cytokine profiles in atherosclerosis.

Immune and inflammatory responses of JAZF1 involving the regulation of at macrophages and T cells

AT macrophages

AT is a connective tissue that is extensively found in the body and contains adipocytes, fibroblasts, vascular endothelial cells, adipocyte stem/progenitor cells, stromal cells, autonomic nerves, numerous immune cells (including mast cells, eosinophils, leukocytes, T cells, B cells, and macrophages), collagen and elastic fibers, nerve bundles, and vasa vasorum.^36,37 Macrophages play various roles at all stages of atherosclerosis development by secreting proinflammatory and anti-inflammatory cytokines. The subtypes of AT macrophages include M1 macrophages, M2 macrophages, oxidized macrophages (Mox macrophages), and metabolically activated macrophages (MMe macrophages). M1 macrophages are induced by proinflammatory cytokines and secrete proinflammatory factors, including CD80, CD86, CD16/32, CD11c, IL-1β, IL-6, IL-12, and TNFα, whereas M2 macrophages inhibit inflammation and repair tissue by overexpressing anti-inflammatory and tissue repair factors, including arginase-1 (Arg-1), CD206, IL-10, IL-1 receptor (IL-1R), CD163, resistin-like molecule β (RELMβ), CCL17 and CCL22.³⁸ In general, M2 macrophages tend to transform into M1 macrophages in AT. AT contributes to atherosclerosis development by increasing the number of M1 macrophages and releasing proinflammatory factors. Mox macrophages account for 30% of plaque macrophages, and M1 and M2 subsets comprise 40% and 20% of the remaining population, respectively. The molecules oxidized phospholipid (Ox-PL), NF-E2-related factor 2 (Nrf2), sulfiredoxin-1 (Srnx-1), heme oxygenase-1 (HO-1), glutamate-cysteine ligase modifier subunit (GCLM), glutathione S-transferase (GST), and thioredoxin reductase-1 (Txnrd-1) are markers of the Mox cell surface. Mox cells are a proatherogenic subset based on their production of proinflammatory cytokines (COX-2 and IL-1β). Genes, including peroxisome proliferator-activated receptor γ (PPARγ), ABCA1, p62, CD36, NADPH oxidase-2 (Nox2), and Perilipin 2 (PLIN2), are markers of MMe cells. Under basal conditions, MMe cells in AT could balance the progression of inflammation. CD36-mediated cholesterol uptake is in balance with ABCA1-mediated cholesterol efflux in MMe cells. However, the state of MMe cells in AT is dynamically regulated by disease states, which can promote a proinflammatory response and cholesterol accumulation and potentially lead to atherosclerosis development.^39,40 Therefore, Mox and MMe cells are the proatherogenic subsets in AT (Fig. 2).

Figure 2.

JAZF1 regulates many cytokines and lipid metabolism genes by regulating the LXRE and CRE sites of the gene promoter. The JAZF1-mediated regulation of SREBP-1c and HMGCR expression via LXRE and CRE sites has been investigated. JAZF1 also regulates IFN-γ, IL-1β, IL-4, IL-6, IL-8, IL-10, TNFα, IL-17, VEGF, SCD-1, FAS, ACC, and FABP4 expression (red). However, the regulatory mechanisms have not been investigated.

As mentioned previously, JAZF1 is most highly expressed in AT. Importantly, in mouse AT, JAZF1 overexpression decreases the number of total AT macrophages (ATMs) and CD11c⁺ ATMs and proinflammatory cytokine secretion (including TNFα and IL-1β) and increases the number of CD206⁺ ATMs.^24,25 JAZF1 deficiency increases the CD68-positive macrophage and monocyte numbers in mouse AT.¹⁰ CD206 is a marker of anti-inflammatory M2 ATMs, whereas CD11c, TNFα, and IL-1β are markers of proinflammatory M1 ATMs, which suggests that JAZF1 suppresses inflammation and atherosclerosis development by promoting M1 macrophage transformation into M2 macrophages in AT.

AT T cells

AT T cells are also associated with atherosclerosis, including γδ T cell, CD4⁺ T cell, CD8⁺ T cell, CD69⁺ T cell, T cytotoxic 1 (Tc1) cell, Th17 cell, Th1 cell, Th2 cell, and CD25⁺FOXP3⁺ Treg cell (Fig. 2).⁴¹ CD4⁺ T cells are involved in the initial stage of AT inflammation during the progression of atherosclerosis. Th1, Tc1, and T17 cells are proatherogenic cells that release pro-inflammatory factors, including IFN-γ, TNFα, and IL-17. Treg and Th2 cells are atheroprotective cells that release IL-10. An HFD promotes lipid accumulation and chronic inflammation in mouse AT by recruiting immune cells (such as CD4⁺ T cell, CD8⁺ T cell, CD69⁺ T cell, and CD44⁺ T cell) and promoting the production of pro-inflammatory cytokines (such as IFN-γ and IL-17), which leads to atherosclerosis development.42, 43, 44 The Th1:Th2 balance in AT is highly associated with systemic inflammation and atherosclerosis development. Overall, AT T cells are extensively involved in the development of atherosclerosis.

JAZF1 also regulates the AT T-cell numbers in vivo. Specifically, JAZF1 increases the number of total T cells and CD25⁺FOXP3⁺ Treg cells but decreases the number of total CD4⁺ T cells, CD69⁺ active T cells, and CD44⁺ memory T cells in the AT of mice. JAZF1 decreases the IFN-γ and IL-17 levels but increases the IL-4 levels in AT CD4⁺ T cells. Notably, ATMs promote AT CD4⁺ T-cell activation by releasing MHCII, CD86, and CD40. JAZF1 decreases CD4⁺ T-cell activation by reducing ATM MHCII, CD86, and CD40 secretion, which suggests that JAZF1 regulates T-cell subtype differentiation by regulating ATM cytokine secretion.^24,25 Overall, JAZF1 suppresses AT inflammation and atherosclerosis development by limiting the macrophage and T-cell populations and their antigen presentation functions.

Lipid metabolism of JAZF1 involving binding to LXREs and serving as a corepressor of TR4

Binding to LXREs

Lipid metabolism dysfunction induces atherosclerosis. Many genes, including acetyl–coenzyme A carboxylase (ACC), adipose triglyceride lipase (ATGL), CCAAT/enhancer binding protein α (C/EBPα), fatty acid synthetase (FAS), fatty acid binding protein 4 (FABP4), stearoyl CoA desaturase-1 (SCD-1), sterol regulatory element–binding protein 1c (SREBP-1c) and hormone-sensitive lipase (HSL), play key roles in lipid metabolism. ACC and FAS are master enzymes in lipid synthesis that are linked to the development of atherosclerosis.^45,46 ATGL is the rate-limiting enzyme that catalyzes the first step of the breakdown of TGs into glycerol and fatty acids.⁴⁷ C/EBPα plays an important role in lipogenesis, VLDL secretion, and lipolysis.⁴⁸ FABP4 is a lipid chaperone that binds fatty acid precursors. FABP4 also promotes macrophage foaming and inflammation by enhancing IL-1β and MMP-9 secretion and CD36 expression, which suggests that FABP4 plays a key role in lipid uptake and the inflammatory response.^49,50 SCD-1 and SREBP-1c have been shown to be the principal regulatory transcription factors for lipid synthesis.^51,52 HSL is the key rate-limiting enzyme that catalyzes AT lipolysis.⁵³

JAZF1 suppresses lipid accumulation and decreases the droplet size by reducing ACC, FAS, SCD-1, and SREBP-1c expression and increasing HSL and ATGL expression in vitro and in vivo.54, 55, 56 JAZF1 deficiency in JAZF1^+/− and JAZF1^−/− mice decrease lipid accumulation by decreasing FABP4 and C/EBPα expression.¹⁰ Thus, JAZF1 decreases lipid accumulation by regulating ACC, FAS, SCD-1, SREBP-1c, HSL, ATGL, FABP4, and C/EBPα expression.

LXREs are necessary for SREBP-1c promoter activities. Interestingly, JAZF1 inhibits SREBP-1c transcription by increasing AMPK phosphorylation and binding to LXREs in the SREBP-1c promoter, which suggests that LXREs play a key role in JAZF1-mediated gene expression.¹³ JAZF1 also regulates SCD-1, FAS, ACC, and FABP4 expression.^10,19,57 However, the mechanism is unclear. Interestingly, the promoters of ACC,⁵⁸ FAS,^59,60 FABP4,⁶¹ and SCD-1⁶² also contain LXREs. Other lipid metabolism genes also contain LXREs, including ABCA1,^63,64 ABCG1,^65,66 long-chain acyl-CoA synthetases 3 (ACSL3),⁶⁷ angiopoietin-like protein 3 (Angptl3),⁶⁸ 3alpha-hydroxysteroid dehydrogenase (AKR1C4),⁶⁹ ADP ribosylation factor like GTPase 4C (Arl4c, also named Arl7),⁷⁰ α-tocopherol transfer protein (α-TTP),⁷¹ cholesteryl ester transfer protein (CETP),⁷² cholesterol 25-hydroxylase (CH25H),⁷³ cholesterol 7-alpha-hydroxylase (CYP7A1),⁷⁴ ileal bile acid-binding protein (I-BABP),⁷⁵ lysophosphatidylcholine acyltransferase 3 (LPCAT3),⁷⁶ lipoprotein lipase (LPL),⁷⁷ midline-1-interacting G12-like protein (MIG12),⁷⁸ organic solute transporter alpha/beta (Ostalpha/beta),⁷⁹ phospholipid transfer protein (PLTP),⁸⁰ group IIA secretory phospholipase A2 (sPLA2),⁸¹ SR-BI,⁸² sulfotransferase family 1E (Sult1e1),⁸³ and UDP-glucuronosyltransferase 1A3 (UGT1A3).⁸⁴ Because JAZF1 regulates SREBP-1c expression via LXREs, we hypothesized that JAZF1 could regulate lipid metabolism by binding to the LXREs of these genes (Fig. 1). However, further studies are needed.

Serving as a corepressor of TR4

JAZF1 is a corepressor of TR4, which inhibits PPARα/β/δ expression by competitively binding to PPREs. PPARα/β/δ promote the transcription and activation of visfatin by binding to the PPRE of the visfatin promoter region.⁸⁵ JAZF1 promotes visfatin promoter activity by upregulating PPARα/β/δ expression in adipocytes. Interestingly, visfatin promotes TG accumulation. However, JAZF1 inhibits lipid accumulation in adipocytes. Indeed, JAZF1 also inhibits PPARγ expression, which is mainly expressed in AT and is an essential regulatory factor associated with lipid accumulation.^86,87 This finding suggests that PPARγ plays a key role in JAZF1-mediated reductions in lipid accumulation. However, JAZF1 deficiency decreases PPARγ expression in JAZF1^+/− and JAZF1^−/− mice, which suggests that JAZF1 may increase PPARγ expression.¹⁰ The effect of JAZF1 on PPARγ may be cell-specific, and more studies are needed to confirm the effect of JAZF1 on PPARγ.

HMGCR is the key rate-limiting enzyme of cholesterol synthesis.⁸⁶ JAZF1 reduces the serum cholesterol levels and hepatic cholesterol synthesis by inhibiting HMGCR expression.¹⁵ The HMGCR promoter has a CRE site (TGACGTAG), which is necessary for CREB activities. JAZF1 suppresses CREB activation by decreasing the phosphorylation of CREB at the Ser133 site. Furthermore, JAZF1 decreases HMGCR expression by suppressing the phosphorylation of CREB.¹⁵ TR4 promotes the phosphorylation of CREB. TR4 also directly promotes lipid accumulation by activating the Fatty acid transport protein 1 (FATP1) and CD36 promoters, which suggests that FATP1 and CD36 are target genes of TR4.^88,89 As mentioned previously, PPARs are also target genes of TR4. JAZF1 is a corepressor of TR4, which suggests that JAZF1 regulates lipid accumulation by regulating the TR4-PPAR, TR4-CREB-HMGCR, TR4-FATP1, and TR4-CD36 axes. In addition, the promoters of SREBP-1c⁹⁰ and PPARγ⁹¹ also contain a CRE site, which suggests that JAZF1 regulates the expression of these genes by regulating the TR4-CREB pathway. Overall, JAZF1 suppresses lipid accumulation by regulating the expression of ACC, ATGL, C/EBPα, FAS, FABP4, HMGCR, HSL, PPARα/β/δ/γ, SCD-1, SREBP-1c, and visfatin, and this regulation mainly depends on LXREs and TR4.

Development of a dual-target compound targeting NF-κB and TAK1 (downstream of JAZF1)

The antiatherosclerotic therapeutic strategies targeting NF-κB were reviewed in 2012.⁹² However, the activity of these drugs (such as aspirin and tepoxalin) in suppressing NF-κB is low. As mentioned previously, NF-κB is the center of the JAZF1-mediated inhibition of the inflammatory response. Transforming growth factor β (TGF-β)-activated kinase 1 (TAK1, also named MAP3K7) is a pivotal kinase upstream of NF-κB. JAZF1 suppresses NF-κB expression by inhibiting TAK1 expression.⁹³ Interestingly, TAK1 inhibition also decreases lipid accumulation.⁹⁴ A positive feedback regulation exists between proinflammatory NF-κB signaling and lipid accumulation.⁹⁵ The design strategy of NF-κB and JAZF1 or TAK1 dual-target compounds could inhibit both inflammation and lipid accumulation. There are no dual-target JAZF1 and NF-κB compounds because JAZF1 is a relatively new target, but dual-target TAK1 and NF-κB compounds exist. Indeed, many dual compounds target NF-κB (Table 1). For example, the dual-target compounds 1–5 exhibit nanomolar inhibition by targeting NF-κB and TAK1, EGFR, or COX-2.96, 97, 98 However, the activity of these compounds in suppressing NF-κB is relatively low (IC₅₀ > 300 nM). Interestingly, compounds 6–14 suppress NF-κB expression with IC₅₀ values ranging from 1.8 nM to 38.6 nM.⁹⁹ Compounds 3–4 are prodrugs that target NF-κB and COX-2. Combined structural modification using a prodrug strategy may enhance the inhibition of NF-κB. However, many studies are needed. In addition, many TAK1 inhibitors have been developed, but their clinical advancement has been limited by a lack of oral bioavailability. HS-276 is a highly selective orally bioavailable TAK1 inhibitor (IC₅₀ = 2.5 nM). HS-276 suppresses the levels of proinflammatory cytokines, such as TNFα, IL-6, and IL-1β.¹⁰⁰ However, the role of HS-276 in NF-κB has not been investigated.

Table 1.

Structure and activities of compounds targeting NF-κB.

Number	Structure	Activity	Reference
Compound 1		NF-κB IC50: 840 nM; TAK1 IC50: 580 nM	96
Compound 2		NF-κB IC50: 300 nM; EGFR IC50: 60.1 nM	97
Compound 3		NF-κB IC50: 600 nM; EGFR IC50: 137 nM	97
Compound 4 (Prodrug)		NF-κB IC50: 620 nM; COX-2 IC50: 680 nM	98
Compound 5 (Prodrug)		NF-κB IC50: 890 nM; COX-2 IC50: 840 nM	98
Compound 6		NF-κB IC50: 4.9 nM	99
Compound 7		NF-κB IC50: 21 nM	99
Compound 8		NF-κB IC50: 9.1 nM	99
Compound 9		NF-κB IC50: 9.87 nM	99
Compound 10		NF-κB IC50: 1.8 nM	99
Compound 11		NF-κB IC50: 38.6 nM	99
Compound 12		NF-κB IC50: 26 nM	99
Compound 13		NF-κB IC50: 5.2 nM	99
Compound 14		NF-κB IC50: 22.1 nM	99
HS-276		TAK1 IC50: 2.5 nM	100

Future directions and challenges

Atherosclerosis is the presumed cause of 40% of all deaths and the leading cause of death in elderly populations. Patients who are actively being treated with statins still have a residual cardiovascular risk even when LDL-C is controlled or decreases below 70 mg/dL.¹⁰¹ Therefore, the identification of new therapeutic targets and the development of new antiatherosclerotic agents are critical. JAZF1 reduces atherosclerosis development by reducing immune and inflammatory responses and lipid metabolism dysfunction (Fig. 3). Thus, JAZF1 may be a new target for the prevention and treatment of atherosclerosis. However, there remain many problems to be investigated. (i) JAZF1 is most highly expressed in AT. JAZF1 also suppresses atherosclerosis development by reducing AT inflammation via limiting the macrophage and T-cell populations and their antigen presentation functions. However, strategies for targeting JAZF1 expression in AT need to be investigated. (ii) LXRE and CRE sites are present in many cytokine and lipid metabolism gene promoters (Table 2). JAZF1 may regulate the expression of these genes by regulating LXRE and CRE sites. However, only SREBP-1c and HMGCR have been investigated. (iii) JAZF1 is a corepressor of TR4. The TR4-FATP1 and TR4-CD36 axes reduce lipid accumulation, but the role of JAZF1 in these axes has not been investigated. (iv) JAZF1 SNPs are associated with T2DM and insulin resistance (IR)-related diseases in humans.¹⁰² The rs864745 SNP of JAZF1 is associated with atherosclerosis. However, the role of other JAZF1 SNPs in atherosclerosis has not been investigated. (v) The noncoding RNA circPTK2 can promote lipolysis and decrease adipogenesis by regulating the miR-182-5p-JAZF1 axis and may be used as a diagnostic marker of cachexia.¹⁰³ However, the role and mechanism of circPTK2 in atherosclerosis have not been investigated. (vi) miR-19b-3p is transferred by macrophage-derived extracellular vesicles (M-EVs) into VSMCs and then promotes VSMC migration and proliferation to induce atherosclerosis development by targeting JAZF1, which suggests that JAZF1 is expressed in M-EVs and is a target gene of miR-19b-3p.¹⁰⁴ However, the roles of JAZF1 in M-EVs in AT, lipid metabolism, and immune and inflammatory responses have not been investigated. (vii) JAZF1-AS1, which is a long noncoding RNA, is located upstream of JAZF1 in overlapping head-to-head gene pairs. JAZF1-AS1 promotes JAZF1 expression by forming double-stranded RNAs. However, JAZF1 does not affect JAZF1-AS1.¹⁰⁵ The role and mechanism of JAZF1-AS1 in atherosclerosis have not been investigated. (viii) JAZF1-overexpressing transgenic mice exhibit reduced atherosclerosis risk factors and atherosclerosis development. However, these mice also show heart failure symptoms. The safety of JAZF1 overexpression in vivo requires extensive evaluation. (viiii) JAZF1 exerts antiatherosclerotic effects in vitro and in animal studies. However, human studies are relatively lacking, and an evaluation of the effects on humans is needed. We thus hope that more scientists will focus on the potential roles of JAZF1 in AT and atherosclerosis and identify new therapeutic targets for this disease.

Figure 3.

Potential mechanism of JAZF1 in atherosclerosis. JAZF1 suppresses inflammation by reducing the NF-κB-mediated secretion of cytokines (including IL-1β, IL-4, IL-6, IL-8, IL-10, TNFα, IFN-γ, IAR-20, COL3A1, laminin, and MCP-1) via the JNK, MAPK, and TAK1 pathways and reducing the AT cell numbers (including M1 macrophages, CD4⁺, and CD69⁺). JAZF1 suppresses lipid accumulation by suppressing SREBP-1c transcription through increasing AMPK phosphorylation and binding to LXREs in the SREBP-1c promoter, suppressing HMGCR transcription by decreasing CREB phosphorylation and binding to CRE in the HMGCR promoter, and suppressing ACC, FAS, SCD-1, HSL, ATGL, FABP4, and C/EBPα expression. JAZF1 may also suppress the TR4-FATP1 and TR4-CD36 axes to reduce lipid accumulation. JAZF1 promotes visfatin expression and accumulation by regulating the TR4-PPARα/β/δ axis. However, this effectiveness is reduced. JAZF1 generally reduces lipid accumulation.

Table 2.

Main physiological functions of genes containing LXRE and CRE sites.

Gene	Function	References
ABCA1	Cholesterol efflux	63,64
ABCG1	Cholesterol efflux	65,66
ACC	Fatty acid synthesis	58
ACSL3	Fatty acid metabolism	67
Angptl3	Triglyceride metabolism	68
AKR1C4	Bile acid biosynthesis, steroid and hormone metabolism	69
Arl7	Cholesterol efflux	70
α-TTP	Vitamin E regulatory protein	71
CETP	Cholesterol metabolism and transportation	72
CH25H	25-Hydroxycholesterol synthesis	73
CYP7A1	Conversion of cholesterol to bile acids	74
FABP4	Fatty acid metabolism and adipocyte differentiation	75
FAS	Fatty acid synthesis	59,60
I-BABP	Enterohepatic circulation of bile acids	75
IFN-γ	Immune and inflammatory responses	26,27
IL-1β	Immune and inflammatory responses	28
IL-4	Immune and inflammatory responses	29
IL-6	Immune and inflammatory responses	30
IL-8	Immune and inflammatory responses	31
IL-10	Immune and inflammatory responses	32
IL-17	Immune and inflammatory responses	34,35
LPCAT3	Phospholipid metabolism	76
LPL	Hydrolysis of circulating triglyceride-rich lipoproteins	77
MIG12	Fatty acid synthesis and TG accumulation	78
Ostalpha/beta	Bile acid absorption	79
PLTP	Phospholipid metabolism	80
PPARγ	Lipid metabolism	91
SCD-1	Monounsaturated fatty acid synthesis	62
sPLA2	Phospholipid metabolism	81
SR-BI	Cholesterol uptake and efflux	82
SREBP-1c	Lipid synthesis	13,90
Sult1e1	Sulfation and inactivation of estrogen	83
TNFα	Immune and inflammatory responses	33
UGT1A3	Bile acid glucuronidation	84
VEGF	Angiogenesis	106

Author contributions

WC and YZ participated in writing-original draft, supervision, and resources. YY, MZ, and WH participated in formal analysis, and investigation. NL and DX participated in conceptualization, writing-review & editing, project administration, and funding acquisition. All authors read and approved the final version of the manuscript.

Conflict of interests

The authors declare that they have no competing interests.

Funding

The authors are grateful for the financial support provided by the Qingdao Major Scientific and Technological Project for Distinguished Scholars (China) (No. 20170103), the Laoshan Major Scientific and Technological Project for Distinguished Scholars (China) (No. 20181030), and the Natural Science Foundation of Shandong Province, China (No. ZR2020MH369).

Abbreviations

ABCA1

ATP-binding cassette transporter A1

ACC

acetyl–coenzyme A carboxylase

ACSL3

long-chain acyl-CoA synthetases 3

AKR1C4

3alpha-hydroxysteroid dehydrogenase

Angptl3

angiopoietin-like protein 3

Arl4c

ADP ribosylation factor-like GTPase 4C

aP2

adipocyte fatty acid-binding protein

Arg-1

arginase-1

AT

adipose tissue

ATGL

adipose triglyceride lipase

ATM

adipose tissue macrophage

CD206

mannose receptor

CETP

cholesteryl ester transfer protein

CHD

coronary heart disease

CH25H

cholesterol 25-hydroxylase

COL3A1

fibrotic gene collagen type III alpha 1

CRE

cAMP responsive element

CYP7A1

cholesterol 7-alpha-hydroxylase

C/EBPα

CCAAT/enhancer-binding protein α

FABP4

fatty acid-binding protein 4

FAs

fatty acids

FAS

fatty acid synthetase

FATP1

fatty acid transport protein 1

GCLM

glutamate-cysteine ligase modifier subunit

GST

glutathione S-transferase

HFD

high-fat diet

HO-1

heme oxygenase-1

HSL

hormone-sensitive lipase

IFN-γ

interferon γ

IL-1R

IL-1 receptor

IL-6

interleukin-6

I-BABP

ileal bile acid-binding protein

JAZF1

juxtapose with another zinc finger gene 1

LPCAT3

lysophosphatidylcholine acyltransferase 3

LPL

lipoprotein lipase

LXREs

liver X receptor response elements

MCP-1

monocyte chemotactic protein 1

MIG12

midline-1-interacting G12-like protein

MMe

metabolically activated macrophage

Mox

oxidized macrophage

Nox2

NADPH oxidase-2

Nrf2

NF-E2-related factor 2

NR2C2

nuclear receptor subfamily 2, group C, member 2

Ostalpha/beta

organic solute transporter alpha/beta

Ox-PL

oxidized phospholipid

PLIN2

perilipin 2

PLTP

phospholipid transfer protein

RELMβ

collagen, resistin-like molecule β

ROS

reactive oxygen species

SCD-1

stearoyl CoA desaturase-1

SNP

single nucleotide polymorphism

sPLA2

group IIA secretory phospholipase A2

SREBP-1c

sterol regulatory element-binding protein 1c

Srnx-1

sulfiredoxin-1

Sult1e1

sulfotransferase family 1E

TAK1

transforming growth factor β-activated kinase 1

Tc1

T cytotoxic 1

TNF-α

tumor necrosis factor-α

TR4

testicular orphan nuclear receptor-4

Txnrd-1

thioredoxin reductase-1

T2DM

type 2 diabetes mellitus

UGT1A3

UDP-glucuronosyltransferase 1A3

VEGF

vascular endothelial growth factor

α-TTP

α-tocopherol transfer protein