Intermedin inhibits macrophage foam-cell formation via tristetraprolin-mediated decay of CD36 mRNA

CD36: a promising therapeutic target in hematologic tumors

Cluster of differentiation 36 (CD36) is a multiligand receptor with important roles in lipid metabolism, angiogenesis and innate immunity, and its diverse effects may depend on the binding of specific ligands in different contexts. CD36 is expressed not only on immune cells in the tumor microenvironment (TME) but also on some hematopoietic cells. CD36 is associated with the growth, metastasis and drug resistance in some hematologic tumors, such as leukemia, lymphoma and myelodysplastic syndrome. Currently, some targeted therapeutic agents against CD36 have been developed, such as anti-CD36 antibodies, CD36 antagonists (small molecules) and CD36 expression inhibitors. This paper not only innovatively addresses the role of CD36 in some hematopoietic cells, such as erythrocytes, hematopoietic stem cells and platelets, but also pays special attention to the role of CD36 in the development of hematologic tumors, and suggests that CD36 may be a potential cancer therapeutic target in hematologic tumors.

MicroRNAs in diabetic macroangiopathy

Diabetic macroangiopathy is a leading cause of diabetes-related mortality worldwide. Both genetic and environmental factors, through a multitude of underlying molecular mechanisms, contribute to the pathogenesis of diabetic macroangiopathy. MicroRNAs (miRNAs), a class of non-coding RNAs known for their functional diversity and expression specificity, are increasingly recognized for their roles in the initiation and progression of diabetes and diabetic macroangiopathy. In this review, we will describe the biogenesis of miRNAs, and summarize their functions in diabetic macroangiopathy, including atherosclerosis, peripheral artery disease, coronary artery disease, and cerebrovascular disease, which are anticipated to provide new insights into future perspectives of miRNAs in basic, translational and clinical research, ultimately advancing the diagnosis, prevention, and treatment of diabetic macroangiopathy.

Leveraging macrophage metabolism for anticancer therapy: opportunities and pitfalls

Tumor-associated macrophages (TAMs) constitute an important part of the tumor microenvironment (TME) that regulates tumor progression. Tumor-derived signals, hypoxia, and competition for nutrients influence TAMs to reprogram their cellular metabolism. This altered metabolic profile creates a symbiotic communication between tumor and other immune cells to support tumor growth. In addition, the metabolic profile of TAMs regulates the expression of immune checkpoint molecules. The dynamic plasticity also allows TAMs to reshape their metabolism in response to modern therapeutic strategies. Therefore, over the years, a significant number of approaches have been implicated to reprogram cancer-promoting metabolism in TAMs. In this review, we discuss the current strategies and pitfalls, along with upcoming promising opportunities in leveraging TAM metabolism for developing better therapeutic approaches against cancer.

The regulatory role of CD36 in hematopoiesis beyond fatty acid uptake

CD36 is a transmembrane glycoprotein, located on surface of numerous cell types. This review is aimed to explore regulatory role of CD36 in hematopoiesis beyond fatty acid uptake. CD36 acts as a pattern recognition receptor, regulates cellular fatty acid homeostasis, and negatively monitors angiogenesis. CD36 also mediates free fatty acid transportation to hematopoietic stem cells in response to infections. During normal physiology and pathophysiology, CD36 significantly participates in the activation and metabolic needs of platelets, macrophages, monocytes, T cells, B cells, and dendritic cells. CD36 has shown a unique relationship with Plasmodium falciparum-infected erythrocytes (PfIEs) as a beneficiary for both parasite and host. CD36 actively participates in pathogenesis of various hematological cancers as a significant prognostic biomarker including AML, HL, and NHL. CD36-targeting antibodies, CD36 antagonists (small molecules), and CD36 expression inhibitors/modulators are used to target CD36, depicting its therapeutic potential. Many preclinical studies or clinical trials were performed to assess CD36 as a therapeutic target; some are still under investigation. This review reflects the role of CD36 in hematopoiesis which requires more consideration in future research.

RNA-binding proteins in vascular inflammation and atherosclerosis

Atherosclerotic cardiovascular disease (ASCVD) remains the major cause of premature death and disability worldwide, even when patients with an established manifestation of atherosclerotic heart disease are optimally treated according to the clinical guidelines. Apart from the epigenetic control of transcription of the genetic information to messenger RNAs (mRNAs), gene expression is tightly controlled at the post-transcriptional level before the initiation of translation. Although mRNAs are traditionally perceived as the messenger molecules that bring genetic information from the nuclear DNA to the cytoplasmic ribosomes for protein synthesis, emerging evidence suggests that processes controlling RNA metabolism, driven by RNA-binding proteins (RBPs), affect cellular function in health and disease. Over the recent years, vascular endothelial cell, smooth muscle cell and immune cell RBPs have emerged as key co- or post-transcriptional regulators of several genes related to vascular inflammation and atherosclerosis. In this review, we provide an overview of cell-specific function of RNA-binding proteins involved in all stages of ASCVD and how this knowledge may be used for the development of novel precision medicine therapeutics.

Surfactant protein A promotes atherosclerosis through mediating macrophage foam cell formation

BACKGROUND

Atherosclerosis is a progressive inflammatory disease where macrophage foam cells play a central role in the pathogenesis. Surfactant protein A (SPA) is a lipid-associating protein involved with regulating macrophage function in various inflammatory diseases. However, the role of SPA in atherosclerosis and macrophage foam cell formation has not been investigated.

METHODS

Primary resident peritoneal macrophages were extracted from wildtype (WT) and SPA deficient (SPA -/- ) mice to determine the functional effects of SPA in macrophage foam cell formation. SPA expression was assessed in healthy vessels and atherosclerotic aortic tissue from the human coronary artery and WT or apolipoprotein e-deficient (ApoE -/- ) mice brachiocephalic arteries fed high fat diets (HFD) for 4 weeks. Hypercholesteremic WT and SPA -/- mice fed a HFD for 6 weeks were investigated for atherosclerotic lesions in vivo .

RESULTS

In vitro experiments revealed that global SPA deficiency reduced intracellular cholesterol accumulation and macrophage foam cell formation. Mechanistically, SPA -/- dramatically decreased CD36 cellular and mRNA expression. SPA expression was increased in atherosclerotic lesions in humans and ApoE -/- mice. In vivo SPA deficiency attenuated atherosclerosis and reduced the number of lesion-associated macrophage foam cells.

CONCLUSIONS

Our results elucidate that SPA is a novel factor for atherosclerosis development. SPA enhances macrophage foam cell formation and atherosclerosis through increasing scavenger receptor cluster of differentiation antigen 36 (CD36) expression.

Role of CD36 in cancer progression, stemness, and targeting

CD36 is highly expressed in diverse tumor types and its expression correlates with advanced stages, poor prognosis, and reduced survival. In cancer cells, CD36: 1) increases fatty acid uptake, reprogramming lipid metabolism; 2) favors cancer cell proliferation, and 3) promotes epithelial-mesenchymal transition. Furthermore, CD36 expression correlates with the expression of cancer stem cell markers and CD36+ cancer cells display increased stemness functional properties, including clonogenicity, chemo- and radioresistance, and metastasis-initiating capability, suggesting CD36 is a marker of the cancer stem cell population. Thus, CD36 has been pointed as a potential therapeutic target in cancer. At present, at least three different types of molecules have been developed for reducing CD36-mediated functions: blocking monoclonal antibodies, small-molecule inhibitors, and compounds that knock-down CD36 expression. Herein, we review the role of CD36 in cancer progression, its participation in stemness control, as well as the efficacy of reported CD36 inhibitors in cancer cell cultures and animal models. Overall, the evidence compiled points that CD36 is a valid target for the development of new anti-cancer therapies.

RNA-Binding Proteins: Emerging Therapeutics for Vascular Dysfunction

Vascular diseases account for a significant number of deaths worldwide, with cardiovascular diseases remaining the leading cause of mortality. This ongoing, ever-increasing burden has made the need for an effective treatment strategy a global priority. Recent advances in regenerative medicine, largely the derivation and use of induced pluripotent stem cell (iPSC) technologies as disease models, have provided powerful tools to study the different cell types that comprise the vascular system, allowing for a greater understanding of the molecular mechanisms behind vascular health. iPSC disease models consequently offer an exciting strategy to deepen our understanding of disease as well as develop new therapeutic avenues with clinical translation. Both transcriptional and post-transcriptional mechanisms are widely accepted to have fundamental roles in orchestrating responses to vascular damage. Recently, iPSC technologies have increased our understanding of RNA-binding proteins (RBPs) in controlling gene expression and cellular functions, providing an insight into the onset and progression of vascular dysfunction. Revelations of such roles within vascular disease states have therefore allowed for a greater clarification of disease mechanisms, aiding the development of novel therapeutic interventions. Here, we discuss newly discovered roles of RBPs within the cardio-vasculature aided by iPSC technologies, as well as examine their therapeutic potential, with a particular focus on the Quaking family of isoforms.

Intermedin attenuates macrophage phagocytosis via regulation of the long noncoding RNA Dnm3os/miR-27b-3p/SLAMF7 axis in a mouse model of atherosclerosis in diabetes

Atherosclerosis in diabetes is a leading cause of cardiovascular complications. Intermedin (IMD) is a calcitonin peptide that is known to inhibit macrophage phagocytosis in atherosclerosis, but the exact mechanism is unclear. We investigate genes that are differentially expressed in response to IMD in hyperglycemic conditions and determine whether they delay the progression of atherosclerosis. An atherosclerotic and diabetic-murine model was generated in 8-week-old male ApoE-/- mice receiving streptozotocin and a high-fat diet. The mouse model was treated with IMD and the expression levels of NF-κB, Dnm3os, miR-27b-3p, and SLAMF7 were detected in plaque tissue and macrophages cultured with high glucose concentrations. Phagocytosis was determined by oxidized-low-density lipoprotein (Ox-LDL) uptake and the interactions among Dnm3os, SLAMF7 and miR-27b-3p were assessed by dual-luciferase reporter assays. The expression of NF-κB, Dnm3os, and SLAMF7 was enhanced in atherosclerotic plaques but decreased by IMD. The suppression of Dnm3os reduced plaque formation in IMD-treated mice even further whereas increased by miR-27b-3p. Dnm3os and SLAMF7 were competitively bind to miR-27b-3p in vivo. In vitro, ox-LDL uptake is elevated in macrophages cultured in hyperglycemic conditions but reduced by IMD. Dual-luciferase assays indicate that Dnm3os positively regulates SLAMF7 through miR-27b-3p expression. In conclusion, Dnm3os is involved in macrophage phagocytosis through the competitive binding of SLAMF7 with miR-27b-3p. IMD induces the suppression of Dnm3os to inhibit macrophage phagocytosis and alleviate atherosclerosis in diabetes.

Intermedin1-53 attenuates atherosclerotic plaque vulnerability by inhibiting CHOP-mediated apoptosis and inflammasome in macrophages

Atherosclerotic plaque vulnerability and rupture increase the risk of acute coronary syndromes. Advanced lesion macrophage apoptosis plays important role in the rupture of atherosclerotic plaque, and endoplasmic reticulum stress (ERS) has been proved to be a key mechanism of macrophage apoptosis. Intermedin (IMD) is a regulator of ERS. Here, we investigated whether IMD enhances atherosclerotic plaque stability by inhibiting ERS-CHOP-mediated apoptosis and subsequent inflammasome in macrophages. We studied the effects of IMD on features of plaque vulnerability in hyperlipemia apolipoprotein E-deficient (ApoE^−/−) mice. Six-week IMD_1-53 infusion significantly reduced atherosclerotic lesion size. Of note, IMD_1-53 lowered lesion macrophage content and necrotic core size and increased fibrous cap thickness and vascular smooth muscle cells (VSMCs) content thus reducing overall plaque vulnerability. Immunohistochemical analysis indicated that IMD_1-53 administration prevented ERS activation in aortic lesions of ApoE^−/− mice, which was further confirmed in oxidized low-density lipoproteins (ox-LDL) induced macrophages. Similar to IMD, taurine (Tau), a non-selective ERS inhibitor significantly reduced atherosclerotic lesion size and plaque vulnerability. Moreover, C/EBP-homologous protein (CHOP), a pro-apoptosis transcription factor involved in ERS, was significantly increased in advanced lesion macrophages, and deficiency of CHOP stabilized atherosclerotic plaques in AopE^−/− mice. IMD_1-53 decreased CHOP level and apoptosis in vivo and in macrophages treated with ox-LDL. In addition, IMD_1-53 infusion ameliorated NLRP3 inflammasome and subsequent proinflammatory cytokines in vivo and in vitro. IMD may attenuate the progression of atherosclerotic lesions and plaque vulnerability by inhibiting ERS-CHOP-mediated macrophage apoptosis, and subsequent NLRP3 triggered inflammation. The inhibitory effect of IMD on ERS-induced macrophages apoptosis was probably mediated by blocking CHOP activation.

The role of CD36 in cardiovascular disease

CD36, also known as the scavenger receptor B2, is a multifunctional receptor widely expressed in various organs. CD36 plays a crucial role in the uptake of long-chain fatty acids, the main metabolic substrate in myocardial tissue. The maturation and transportation of CD36 is regulated by post-translational modifications, including phosphorylation, ubiquitination, glycosylation, and palmitoylation. CD36 is decreased in pathological cardiac hypertrophy caused by ischaemia-reperfusion and pressure overload, and increased in diabetic cardiomyopathy and atherosclerosis. Deficiency of CD36 alleviates diabetic cardiomyopathy and atherosclerosis, while overexpression of CD36 eliminates ischaemia-reperfusion damage, together suggesting that CD36 is closely associated with the progression of cardiovascular diseases and may be a new therapeutic target. This review summarizes the regulation and post-translational modifications of CD36 and evaluates its role in cardiovascular diseases and its potential as a therapeutic target.

Shikonin attenuates hyperhomocysteinemia-induced CD4+ T cell inflammatory activation and atherosclerosis in ApoE-/- mice by metabolic suppression

T cell metabolic activation plays a crucial role in inflammation of atherosclerosis. Shikonin (SKN), a natural naphthoquinone with anti-inflammatory activity, has shown to exert cardioprotective effects, but the effect of SKN on atherosclerosis is unclear. In addition, SKN was found to inhibit glycolysis via targeting pyruvate kinase muscle isozyme 2 (PKM2). In the present study, we investigated the effects of SKN on hyperhomocysteinemia (HHcy)-accelerated atherosclerosis and T cell inflammatory activation in ApoE^-/- mice and the metabolic mechanisms in this process. Drinking water supplemented with Hcy (1.8 g/L) was administered to ApoE^-/- mice for 2 weeks and the mice were injected with SKN (1.2 mg/kg, i.p.) or vehicle every 3 days. We showed that SKN treatment markedly attenuated HHcy-accelerated atherosclerosis in ApoE^-/- mice and significantly decreased inflammatory activated CD4⁺ T cells and proinflammatory macrophages in plaques. In splenic CD4⁺ T cells isolated from HHcy-ApoE^-/- mice, SKN treatment significantly inhibited HHcy-stimulated PKM2 activity, interferon-γ secretion and the capacity of these T cells to promote macrophage proinflammatory polarization. SKN treatment significantly inhibited HHcy-stimulated CD4⁺ T cell glycolysis and oxidative phosphorylation. Metabolic profiling analysis of CD4⁺ T cells revealed that Hcy administration significantly increased various glucose metabolites as well as lipids and acetyl-CoA carboxylase 1, which were reversed by SKN treatment. In conclusion, our results suggest that SKN is effective to ameliorate atherosclerosis in HHcy-ApoE^-/- mice and this is at least partly associated with the inhibition of SKN on CD4⁺ T cell inflammatory activation via PKM2-dependent metabolic suppression.

Altered Expression of Adrenomedullin 2 and its Receptor in the Adipose Tissue of Obese Patients

CONTEXT

Adrenomedullin 2 (AM2) plays protective roles in the renal and cardiovascular systems. Recent studies in experimental animals demonstrated that AM2 is an adipokine with beneficial effects on energy metabolism. However, there is little information regarding AM2 expression in human adipose tissue.

OBJECTIVE

To investigate the pattern and regulation of the expression of AM2 and its receptor component in human adipose tissue, in the context of obesity and type 2 diabetes.

METHODS

We measured metabolic parameters, serum AM2, and expression of ADM2 and its receptor component genes in abdominal subcutaneous and visceral adipose tissue in obese (with or without type 2 diabetes) and normal-weight women. Serum AM2 was assessed before and 6 to 9 months after bariatric surgery. Expression/secretion of AM2 and its receptor were assessed in human adipocytes.

RESULTS

ADM2 mRNA in both fat depots was higher in obese patients, whether diabetic or not. Although serum AM2 was significantly lower in obese patients, it was not changed after bariatric surgery. AM2 and its receptor complex were predominantly expressed by adipocytes, and the expression of CALCRL, encoding a component of the AM2 receptor complex, was lower in both fat depots of obese patients. Incubating adipocytes with substances mimicking the microenvironment of obese adipose tissue increased ADM2 mRNA but reduced both AM2 secretion into culture media and CALCRL mRNA expression.

CONCLUSIONS

Our data indicate that AM2 signaling is suppressed in adipose tissue in obesity, involving lower receptor expression and ligand availability, likely contributing to insulin resistance and other aspects of the pathophysiology associated with obesity.

Intermedin1-53 Ameliorates Homocysteine-Promoted Atherosclerotic Calcification by Inhibiting Endoplasmic Reticulum Stress

Aim:

Vascular calcification (VC) is thought to be an independent predictor of cardiovascular morbidity and mortality. Intermedin1-53 (IMD) is a cardiovascular protective peptide and can inhibit vascular medial calcification in rats. In this study, we investigated the effect of IMD on atherosclerotic calcification induced by a high-fat diet plus homocysteine (Hcy) and the potential mechanisms.

Methods:

ApoE−/− mice were fed a high-fat diet with Hcy in drinking water to induce atherosclerotic calcification.

Results:

As compared to the high-fat diet alone, Hcy treatment significantly increased atherosclerotic lesion areas and the number of calcified nodules in aortic roots and was reduced by IMD infusion or 4-phenylbutyric acid (PBA) treatment. In vitro, as compared to calcifying medium alone, Hcy treatment further increased alkaline phosphatase activity, calcium content, and calcium nodule number in human aorta vascular smooth muscle cells (HA-VSMCs), all blocked by IMD or PBA pretreatment. Mechanistically, IMD or PBA significantly alleviated endoplasmic reticulum stress (ERS) activation compared with Hcy treatment. In parallel, IMD or PBA attenuated the messenger RNA levels of osteogenic markers and inflammatory cytokines in aortas and their protein levels in lesions of aortic roots. In vitro, Hcy treatment significantly increased the protein levels of osteoblast-like cell markers in primary rat VSMCs and inflammation markers in mouse peritoneal macrophages, all decreased with IMD or PBA pretreatment. Intermedin1-53 pretreatment also markedly reduced the protein levels of ERS markers in rat VSMCs and mouse peritoneal macrophages.

Conclusions:

Intermedin1-53 protects against Hcy-promoted atherosclerotic calcification in ApoE−/− mice by inhibiting ERS.

Inhibition of endoplasmic reticulum stress by intermedin1-53 attenuates angiotensin II-induced abdominal aortic aneurysm in ApoE KO Mice

Endoplasmic reticulum stress (ERS) is involved in the development of abdominal aortic aneurysm (AAA). Since bioactive peptide intermedin (IMD)1-53 protects against AAA formation, here we investigated whether IMD1-53 attenuates AAA by inhibiting ERS. AAA model was induced by angiotensin II (AngII) in ApoE KO mouse background. AngII-treated mouse aortas showed increased ERS gene transcription of caspase12, eukaryotic translation initiation factor 2a (eIf2a) and activating transcription factor 4(ATF4).The protein level of ERS marker glucose regulated protein 94(GRP94), ATF4 and C/EBP homologous protein 10(CHOP) was also up-regulated by AngII. Increased ERS levels were accompanied by severe VSMC apoptosis in human AAA aorta. In vivo administration of IMD1-53 greatly reduced AngII-induced AAA and abrogated the activation of ERS. To determine whether IMD inhibited AAA by ameliorating ERS, we used 2 non-selective ERS inhibitors phenyl butyrate (4-PBA) and taurine (TAU). Similar to IMD, PBA, and TAU significantly reduced the incidence of AAA and AAA-related pathological disorders. In vitro, AngII infusion up-regulated CHOP, caspase12 expression and led to VSMC apoptosis. IMD siRNA aggravated the CHOP, caspase12-mediated VSMC apoptosis, which was abolished by ATF4 silencing. IMD infusion promoted the phosphorylation of adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) in aortas in ApoE KO mice, and the AMPK inhibitor compound C abolished the protective effect of IMD on VSMC ERS and apoptosis induced by AngII. In conclusion, IMD may protect against AAA formation by inhibiting ERS via activating AMPK phosphorylation.

RBPs Play Important Roles in Vascular Endothelial Dysfunction Under Diabetic Conditions

Diabetes is one of the major health care problems worldwide leading to huge suffering and burden to patients and society. Diabetes is also considered as a cardiovascular disorder because of the correlation between diabetes and an increased incidence of cardiovascular disease. Vascular endothelial cell dysfunction is a major mediator of diabetic vascular complications. It has been established that diabetes contributes to significant alteration of the gene expression profile of vascular endothelial cells. Post-transcriptional regulation by RNA binding proteins (RBPs) plays an important role in the alteration of gene expression profile under diabetic conditions. The review focuses on the roles and mechanisms of critical RBPs toward diabetic vascular endothelial dysfunction. Deeper understanding of the post- transcriptional regulation by RBPs could lead to new therapeutic strategies against diabetic manifestation in the future.

Andrographolide Inhibits Oxidized LDL-Induced Cholesterol Accumulation and Foam Cell Formation in Macrophages

oxLDL is involved in the pathogenesis of atherosclerotic lesions through cholesterol accumulation in macrophage foam cells. Andrographolide, the bioactive component of Andrographis paniculata, possesses several biological activities such as anti-inflammatory, anti-oxidant, and anticancer functions. Scavenger receptors (SRs), including class A SR (SR-A) and CD36, are responsible for the internalization of oxLDL. In contrast, receptors for reverse cholesterol transport, including ABCA1 and ABCG1, mediate the efflux of cholesterol from macrophage foam cells. Transcription factor liver X receptor [Formula: see text] (LXR[Formula: see text] plays a key role in lipid metabolism and inflammation as well as in the regulation of ABCA1 and ABCG1 expression. Because of the contribution of inflammation to macrophage foam cell formation and the potent anti-inflammatory activity of andrographolide, we hypothesized that andrographolide might inhibit oxLDL-induced macrophage foam cell formation. The results showed that andrographolide reduced oxLDL-induced lipid accumulation in macrophage foam cells. Andrographolide decreased the mRNA and protein expression of CD36 by inducing the degradation of CD36 mRNA; however, andrographolide had no effect on SR-A expression. In contrast, andrographolide increased the mRNA and protein expression of ABCA1 and ABCG1, which were dependent on LXR[Formula: see text]. Andrographolide enhanced LXR[Formula: see text] nuclear translocation and DNA binding activity. Treatment with the LXR[Formula: see text] antagonist GGPP and transfection with LXR[Formula: see text] siRNA reversed the ability of andrographolide to stimulate ABCA1 and ABCG1 protein expression. In conclusion, inhibition of CD36-mediated oxLDL uptake and induction of ABCA1- and ABCG1-dependent cholesterol efflux are two working mechanisms by which andrographolide inhibits macrophage foam cell formation, which suggests that andrographolide could be a potential candidate to prevent atherosclerosis.

Intermedin reduces neointima formation by regulating vascular smooth muscle cell phenotype via cAMP/PKA pathway

BACKGROUND AND AIMS

Vascular smooth muscle cell (VSMC) dedifferentiation contributes to neointima formation, which results in various vascular disorders. Intermedin (IMD), a cardiovascular paracrine/autocrine polypeptide, is involved in maintaining circulatory homeostasis. However, whether IMD protects against neointima formation remains largely unknown. The purpose of this study is to investigate the role of IMD in neointima formation and the possible mechanism.

METHODS

IMD_1-53 (100ng/kg/h) or saline water was used on rat carotid-artery balloon-injury model. The mouse left common carotid-artery ligation-injury model was established using IMD-transgenic and C57BL/6J mice. Immunohistochemistry and immunofluorescence staining was used to detect the protein expression in rat carotid arteries. Radioimmunoassay was used to determine the serum IMD level. The hematoxylin andeosin staining was used for carotid arteries morphological testing. In vitro, for rat primary cultured VSMC phenotype transition, proliferation and migration assays, platelet-derived growth factor-BB (PDGF-BB) reagent and IMD_1-53 peptide were added to the culture media at the final concentration of 20 ng/mL and 10^-7mol/L respectively. Quantification of VSMC proliferation involved MTT and BrdU assay and migration was detected by wound-healing assay. Western blot and realtime PCR were used to detect the protein and mRNA levels of tissues or cells.

RESULTS

With the rat carotid-artery balloon-injury model, IMD was significantly downregulated in injured arteries and plasma. Exogenous IMD_1-53 greatly inhibited neointima formation and prevented VSMC from switching to a synthetic phenotype. With the left common carotid-artery ligation-injury model, IMD-transgenic mice showed less neointima formation than C57BL/6J mice. PDGF-BB reduced IMD mRNA expression in rat primary cultured VSMCs but increased that of its receptors, calcitonin receptor-like receptor or receptor activity-modifying proteins. Furthermore, PDGF-BB promoted VSMC proliferation and migration and transformed VSMCs to the synthetic phenotype, which was reversed with IMD_1-53 treatment. Mechanistically, IMD_1-53 maintained the contractile VSMC phenotype via the cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) pathway.

CONCLUSIONS

IMD attenuated neointima formation both in the rat model of carotid-artery balloon injury and mouse model of common carotid-artery ligation injury. IMD protection may be mediated by maintaining a VSMC contractile phenotype via the cAMP/PKA pathway.

Adrenomedullin 2/intermedin: a putative drug candidate for treatment of cardiometabolic diseases

Adrenomedullin (ADM) 2/intermedin (IMD) is a short peptide that belongs to the CGRP superfamily. Although it shares receptors with CGRP, ADM and amylin, ADM2 has significant and unique functions in the cardiovascular system. In the past decade, the cardiovascular effect of ADM2 has been carefully analysed. In this review, progress in understanding the effects of ADM2 on the cardiovascular system and its protective role in cardiometabolic diseases are summarized.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

Calcitonin Peptide Family Members Are Differentially Regulated by LPS and Inhibit Functions of Rat Alveolar NR8383 Macrophages

Members of the calcitonin peptide family—calcitonin gene-related peptide (CGRP), adrenomedullin (AM), and adrenomedullin2/intermedin (IMD)–exert modulatory effects upon monocytes and macrophages of various extrapulmonary origins. Utilizing the rat alveolar macrophage (AMφ) cell line NR8383, we here set out to determine to which extent these three peptides and their receptors are differentially regulated in AMφ and what specific effects they have on AMφ key functions. LPS treatment differentially up-regulated expression of the peptides and receptors. Among the three peptides, IMD mRNA content was lowest both in primary rat AMφ and NR8383 cells, whereas IMD peptide dominated in basal and LPS-stimulated secretion from NR8383 cells. Fcγ receptor-mediated phagocytosis and TNF-α production were inhibited by AM, IMD, and CGRP, whereas pro-IL-1β mRNA was slightly down-regulated exclusively by CGRP. Neither of these peptides affected IL-6 or IL-10 production. None increased intracellular calcium concentration, but AM significantly inhibited store-operated calcium entry. In conclusion, the rat AMφ cell line NR8383 is both a source and a target of the calcitonin peptide family members AM, IMD, and CGRP. Despite sharing proteins of the receptor complexes, AM, IMD, and CGRP each showed a characteristic pattern of effects and regulation, suggesting that these closely related peptides are not just redundant members of one common signaling pathway but act in concert by addressing parallel signaling cascades. Since peptide and receptor expression are up-regulated by LPS, these signaling pathways might act as inhibitory feedback mechanisms in pulmonary bacterial infection.

Adrenomedullin 2 Enhances Beiging in White Adipose Tissue Directly in an Adipocyte-autonomous Manner and Indirectly through Activation of M2 Macrophages

Adrenomedullin 2 (ADM2) is an endogenous bioactive peptide belonging to the calcitonin gene-related peptide family. Our previous studies showed that overexpression of ADM2 in mice reduced obesity and insulin resistance by increasing thermogenesis in brown adipose tissue. However, the effects of ADM2 in another type of thermogenic adipocyte, beige adipocytes, remain to be understood. The plasma ADM2 levels were inversely correlated with obesity in humans, and adipo-ADM2-transgenic (tg) mice displayed resistance to high-fat diet-induced obesity with increased energy expenditure. Beiging of subcutaneous white adipose tissues (WAT) was more noticeably induced in high-fat diet-fed transgenic mice with adipocyte-ADM2 overexpression (adipo-ADM2-tg mice) than in WT animals. ADM2 treatment in primary rat subcutaneous adipocytes induced beiging with up-regulation of UCP1 and beiging-related marker genes and increased mitochondrial uncoupling respiration, which was mainly mediated by activation of the calcitonin receptor-like receptor (CRLR)·receptor activity-modifying protein 1 (RAMP1) complex and PKA and p38 MAPK signaling pathways. Importantly, this adipocyte-autonomous beiging effect by ADM2 was translatable to human primary adipocytes. In addition, M2 macrophage activation also contributed to the beiging effects of ADM2 through catecholamine secretion. Therefore, our study reveals that ADM2 enhances subcutaneous WAT beiging via a direct effect by activating the CRLR·RAMP1-cAMP/PKA and p38 MAPK pathways in white adipocytes and via an indirect effect by stimulating alternative M2 polarization in macrophages. Through both mechanisms, beiging of WAT by ADM2 results in increased energy expenditure and reduced obesity, suggesting ADM2 as a novel anti-obesity target.

Adrenomedullin 2 Improves Early Obesity-Induced Adipose Insulin Resistance by Inhibiting the Class II MHC in Adipocytes

MHC class II (MHCII) antigen presentation in adipocytes was reported to trigger early adipose inflammation and insulin resistance. However, the benefits of MHCII inhibition in adipocytes remain largely unknown. Here, we showed that human plasma polypeptide adrenomedullin 2 (ADM2) levels were negatively correlated with HOMA of insulin resistance in obese human. Adipose-specific human ADM2 transgenic (aADM2-tg) mice were generated. The aADM2-tg mice displayed improvements in high-fat diet-induced early adipose insulin resistance. This was associated with increased insulin signaling and decreased systemic inflammation. ADM2 dose-dependently inhibited CIITA-induced MHCII expression by increasing Blimp1 expression in a CRLR/RAMP1-cAMP-dependent manner in cultured adipocytes. Furthermore, ADM2 treatment restored the high-fat diet-induced early insulin resistance in adipose tissue, mainly via inhibition of adipocyte MHCII antigen presentation and CD4(+) T-cell activation. This study demonstrates that ADM2 is a promising candidate for the treatment of early obesity-induced insulin resistance.

Intermedin Restores Hyperhomocysteinemia-induced Macrophage Polarization and Improves Insulin Resistance in Mice

Hyperhomocysteinemia (HHcy) is a condition characterized by an abnormally high level of homocysteine, an inflammatory factor. This condition has been suggested to promote insulin resistance. To date, the underlying molecular mechanism remains largely unknown, and identifying novel therapeutic targets for HHcy-induced insulin resistance is of high priority. It is well known that intermedin (IMD), a calcitonin family peptide, exerts potent anti-inflammatory effects. In this study, the effects of IMD on HHcy-induced insulin resistance were investigated. Glucose tolerance and insulin tolerance tests were performed on mice treated with IMD by minipump implantation (318 ng/kg/h for 4 weeks) or adipocyte-specific IMD overexpression mice (Adipo-IMD transgenic mice). The expression of genes and proteins related to M1/M2 macrophages and endoplasmic reticulum stress (ERS) was evaluated in adipose tissues or cells. The expression of IMD was identified to be lower in the plasma and adipose tissues of HHcy mice. In both IMD treatment by minipump implantation and Adipo-IMD transgenic mice, IMD reversed HHcy-induced insulin resistance, as revealed by glucose tolerance and insulin tolerance tests. Further mechanistic study revealed that IMD reversed the Hcy-elevated ratio of M1/M2 macrophages by inhibiting AMP-activated protein kinase activity. Adipo-IMD transgenic mice displayed reduced ERS and lower inflammation in adipose tissues with HHcy. Soluble factors from Hcy-treated macrophages induced adipocyte ERS, which was reversed by IMD treatment. These findings revealed that IMD treatment restores the M1/M2 balance, inhibits chronic inflammation in adipose tissues, and improves systemic insulin sensitivity of HHcy mice.

Prognostic Value of Plasma Intermedin Level in Patients With Non-ST-Segment Elevation Acute Coronary Syndrome

Intermedin (IMD), an autocrine/paracrine biologically active peptide, plays a critical role in maintaining vascular homeostasis. Recent research has shown that high plasma levels of IMD are associated with poor outcomes for patients with ST-segment elevation acute myocardial infarction. However, the prognostic utility of IMD levels in non-ST-segment elevation acute coronary syndrome (NSTE-ACS) has not yet been investigated. We hypothesized that the level of plasma IMD would have prognostic value in patients with NSTE-ACS. Plasma IMD was determined by radioimmunoassay in 132 NSTE-ACS patients on admission to hospital and 132 sex- and age-matched healthy-control subjects. Major adverse cardiovascular events (MACEs), including death, heart failure, hospitalization, and acute myocardial infarction, were noted during follow-up. In total, 23 patients suffered MACEs during the follow-up period (mean 227 ± 118 days, range 2-421 days). Median IMD levels were higher in NSTE-ACS patients than control [320.0 (250.9/384.6) vs. 227.2 (179.7/286.9) pg/mL, P <0.001]. The area under the receiver-operating characteristic curve for IMD and N-terminal pro-B-type brain natriuretic peptide (NT-proBNP) did not significantly differ (0.73 and 0.79, both P <0.001, respectively; P = 0.946). ROC curve analysis revealed a cut-off value for IMD at 340.7 pg/mL. Cox regression analysis with cardiovascular risk variables and NT-proBNP showed that the risk of MACEs increased by a factor of 12.96 (95% CI, 3.26-49.42; P <0.001) with high IMD levels (at the cut-off value). IMD has potential as a prognostic biomarker for predicting MACEs in patients with NSTE-ACS.

Leucine supplementation via drinking water reduces atherosclerotic lesions in apoE null mice

AIM

Recent evidence suggests that the essential amino acid leucine may be involved in systemic cholesterol metabolism. In this study, we investigated the effects of leucine supplementation on the development of atherosclerosis in apoE null mice.

METHODS

ApoE null mice were fed with chow supplemented with leucine (1.5% w/v) in drinking water for 8 week. Aortic atherosclerotic lesions were examined using Oil Red O staining. Plasma lipoprotein-cholesterol levels were measured with fast protein liquid chromatography. Hepatic gene expression was detected using real-time PCR and Western blot analyses.

RESULTS

Leucine supplementation resulted in 57.6% reduction of aortic atherosclerotic lesion area in apoE null mice, accompanied by 41.2% decrease of serum LDL-C levels and 40.2% increase of serum HDL-C levels. The body weight, food intake and blood glucose level were not affected by leucine supplementation. Furthermore, leucine supplementation increased the expression of Abcg5 and Abcg8 (that were involved in hepatic cholesterol efflux) by 1.28- and 0.86-fold, respectively, and significantly increased their protein levels. Leucine supplementation also increased the expression of Srebf1, Scd1 and Pgc1b (that were involved in hepatic triglyceride metabolism) by 3.73-, 1.35- and 1.71-fold, respectively. Consequently, leucine supplementation resulted in 51.77% reduction of liver cholesterol content and 2.2-fold increase of liver triglyceride content. Additionally, leucine supplementation did not affect the serum levels of IL-6, IFN-γ, TNF-α, IL-10 and IL-12, but markedly decreased the serum level of MCP-1.

CONCLUSION

Leucine supplementation effectively attenuates atherosclerosis in apoE null mice by improving the plasma lipid profile and reducing systemic inflammation.

Intermedin/adrenomedullin 2 polypeptide promotes adipose tissue browning and reduces high-fat diet-induced obesity and insulin resistance in mice

OBJECTIVES

There is an urgent need to develop interventions and policies to mitigate the health effects of obesity by targeting its metabolic mediators. Adrenomedullin 2 (AM2)/intermedin (IMD) is a secreted peptide that has an important role in protecting the cardiovascular system. However, the role of AM2 in type 2 diabetes is unknown.

METHODS

Wild-type (WT) and aP2/AM2 transgenic (aAM2-tg) mice were fed a high-fat diet (HFD) for 8 weeks, and WT mice were treated with AM2 through mini-osmotic pumps. Indirect calorimetry, ambulatory activity and food intake, hyperinsulinemic-euglycemic clamp test, glucose and insulin tolerance tests were used for assessing insulin resistance. Rat primary adipocytes and pre-adipocyte-derived adipocytes were used for in vitro experiments. Real-time PCR and western blot were used for analyses of gene expression and protein level.

RESULTS

AM2 and receptor activity-modifying proteins expressions were significantly decreased in the adipose tissue of obese mice. AM2 treatment significantly reduced blood glucose, fasting serum insulin and free fatty acid levels, improved glucose tolerance and insulin sensitivity, and increased the glucose infusion rate during a hyperinsulinemic-euglycemic clamp test, indicating ameliorated HFD-induced insulin resistance. These effects were consistently observed in aAM2-tg mice under HFD conditions, whereas the aAM2-tg mice showed less weight gain and improved glucose tolerance and insulin sensitivity. More importantly, the aAM2-tg mice had increased oxygen consumption and CO2 production, reflecting more energy expenditure. These effects may be due to increased AMP-activated protein kinase phosphorylation and reduced peroxisome proliferator-activated receptor gamma co-activator 1α (PGC1α) acetylation, which result in interactions between PGC1α and PR domain containing 16 and then promote uncoupling protein 1 (UCP1) expression in adipocytes.

CONCLUSIONS

These results indicate that endogenous AM2 might be involved in energy metabolism in adipocytes through the upregulation of UCP1 expression.

Post-transcriptional gene regulation by RNA-binding proteins in vascular endothelial dysfunction

Endothelial cell dysfunction is a term which implies the dysregulation of normal endothelial cell functions, including impairment of the barrier functions, control of vascular tone, disturbance of proliferative and migratory capacity of endothelial cells, as well as control of leukocyte trafficking. Endothelial dysfunction is an early step in vascular inflammatory diseases such as atherosclerosis, diabetic vascular complications, sepsis-induced or severe virus infection-induced organ injuries. The expressions of inflammatory cytokines and vascular adhesion molecules induced by various stimuli, such as modified lipids, smoking, advanced glycation end products and bacteria toxin, significantly contribute to the development of endothelial dysfunction. The transcriptional regulation of inflammatory cytokines and vascular adhesion molecules has been well-studied. However, the regulation of those gene expressions at post-transcriptional level is emerging. RNA-binding proteins have emerged as critical regulators of gene expression acting predominantly at the post-transcriptional level in microRNA-dependent or independent manners. This review summarizes the latest insights into the roles of RNA-binding proteins in controlling vascular endothelial cell functions and their contribution to the pathogenesis of vascular inflammatory diseases.

Endothelial dysfunction in tristetraprolin-deficient mice is not caused by enhanced tumor necrosis factor-α expression

Cardiovascular events are important co-morbidities in patients with chronic inflammatory diseases like rheumatoid arthritis. Tristetraprolin (TTP) regulates pro-inflammatory processes through mRNA destabilization and therefore TTP-deficient mice (TTP(-/-) mice) develop a chronic inflammation resembling human rheumatoid arthritis. We used this mouse model to evaluate molecular signaling pathways contributing to the enhanced atherosclerotic risk in chronic inflammatory diseases. In the aorta of TTP(-/-) mice we observed elevated mRNA expression of known TTP targets like tumor necrosis factor-α (TNF-α) and macrophage inflammatory protein-1α, as well as of other pro-atherosclerotic mediators, like Calgranulin A, Cathepsin S, and Osteopontin. Independent of cholesterol levels TTP(-/-) mice showed a significant reduction of acetylcholine-induced, nitric oxide-mediated vasorelaxation. The endothelial dysfunction in TTP(-/-) mice was associated with increased levels of reactive oxygen and nitrogen species (RONS), indicating an enhanced nitric oxide inactivation by RONS in the TTP(-/-) animals. The altered RONS generation correlates with increased expression of NADPH oxidase 2 (Nox2) resulting from enhanced Nox2 mRNA stability. Although TNF-α is believed to be a central mediator of inflammation-driven atherosclerosis, genetic inactivation of TNF-α neither improved endothelial function nor normalized Nox2 expression or RONS production in TTP(-/-) animals. Systemic inflammation caused by TTP deficiency leads to endothelial dysfunction. This process is independent of cholesterol and not mediated by TNF-α solely. Thus, other mediators, which need to be identified, contribute to enhanced cardiovascular risk in chronic inflammatory diseases.