C1q/TNF-related protein 9 inhibits the cholesterol-induced Vascular smooth muscle cell phenotype switch and cell dysfunction by activating AMP-dependent kinase

Cellular Senescence: A Bridge Between Diabetes and Microangiopathy

Cellular senescence is a state of permanent cell cycle arrest and plays an important role in many vascular lesions. This study found that the cells of diabetic patients have more characteristics of senescence, which may cause microvascular complications. Cell senescence, as one of the common fates of cells, links microangiopathy and diabetes. Cell senescence in a high-glucose environment can partially elucidate the mechanism of diabetic microangiopathy, and various types of cellular senescence induced by it can promote the progression of diabetic microangiopathy. Still, the molecular mechanism of microangiopathy-related cellular senescence has not yet been clearly studied. Building on recent research evidence, we herein summarize the fundamental mechanisms underlying the development of cellular senescence in various microangiopathies associated with diabetes. We gradually explain how cellular senescence serves as a key driver of diabetic microangiopathy. At the same time, the treatment of basic senescence mechanisms such as cellular senescence may have a great impact on the pathogenesis of the disease, may be more effective in preventing the development of diabetic microangiopathy, and may provide new ideas for the clinical treatment and prognosis of diabetic microangiopathy.

CTRP9: An Anti-Atherosclerotic Factor in ApoE Knockout Mice through Oxidative Stress Inhibition

BACKGROUND

C1q/tumor necrosis factor-related protein-9 (CTRP9) is critically involved in the pathophysiology of metabolic and cardiovascular disorders. This investigation aimed to clarify the mechanism underlying the role of CTRP9 in atherosclerosis in apolipoprotein E (ApoE) knockout (KO) mice.

METHODS

ApoE KO mice were fed a Western diet and injected with a virus which resulted in CTRP9 overexpression or knockdown for 12 weeks. The plasma lipid levels and atherosclerotic plaque areas were measured after the mice were euthanized. Aortas were isolated, and RNA sequencing was performed to identify the differentially expressed genes and related signaling pathways. Finally, plasma oxidative stress factors were measured to demonstrate the reliability of the RNA sequencing results.

RESULTS

The plasma lipid levels in the CTRP9 overexpression group did not significantly differ from those in the green fluorescence protein (GFP) group. Markablely, CTRP9 overexpression inhibited atherosclerotic plaque formation in ApoE KO mice, whereas CTRP9 knockdown promoted plaque formation. RNA sequencing analysis identified 3485 differentially expressed genes that were prominently enriched across 55 signaling pathways. Additionally, plasma oxidative stress factors were significantly reduced after CTRP9 overexpression, whereas these factors were increased after CTRP9 knockdown, which was consistent with the results of the RNA sequencing analysis.

CONCLUSIONS

These findings demonstrated that CTRP9 alleviated inflammation and cholesterol metabolism, which reduced oxidative stress in an atherosclerotic animal model. These beneficial effects may mediate the suppression of lesion development in the aorta.

Macrophages in vascular disease: Roles of mitochondria and metabolic mechanisms

Macrophages are a dynamic cell type of the immune system implicated in the pathophysiology of vascular diseases and are a major contributor to pathological inflammation. Excessive macrophage accumulation, activation, and polarization is observed in aortic aneurysm (AA), atherosclerosis, and pulmonary arterial hypertension. In general, macrophages become activated and polarized to a pro-inflammatory phenotype, which dramatically changes cell behavior to become pro-inflammatory and infiltrative. These cell types become cumbersome and fail to be cleared by normal mechanisms such as autophagy. The result is a hyper-inflammatory environment causing the recruitment of adjacent cells and circulating immune cells to further augment the inflammatory response. In AA, this leads to excessive ECM degradation and chemokine secretion, ultimately causing macrophages to dominate the immune cell landscape in the aortic wall. In atherosclerosis, monocytes are recruited to the vascular wall, where they polarize to the pro-inflammatory phenotype and induce inflammatory pathway activation. This leads to the development of foam cells, which significantly contribute to neointima and necrotic core formation in atherosclerotic plaques. Pro-inflammatory macrophages, which affect other vascular diseases, present with fragmented mitochondria and corresponding metabolic dysfunction. Targeting macrophage mitochondrial dynamics has proved to be an exciting potential therapeutic approach to combat vascular disease. This review will summarize mitochondrial and metabolic mechanisms of macrophage activation, polarization, and accumulation in vascular diseases.

Navigating the Maze of Kinases: CaMK-like Family Protein Kinases and Their Role in Atherosclerosis

Circulating low-density lipoprotein (LDL) levels are a major risk factor for cardiovascular diseases (CVD), and even though current treatment strategies focusing on lowering lipid levels are effective, CVD remains the primary cause of death worldwide. Atherosclerosis is the major cause of CVD and is a chronic inflammatory condition in which various cell types and protein kinases play a crucial role. However, the underlying mechanisms of atherosclerosis are not entirely understood yet. Notably, protein kinases are highly druggable targets and represent, therefore, a novel way to target atherosclerosis. In this review, the potential role of the calcium/calmodulin-dependent protein kinase-like (CaMKL) family and its role in atherosclerosis will be discussed. This family consists of 12 subfamilies, among which are the well-described and conserved liver kinase B1 (LKB1) and 5' adenosine monophosphate-activated protein kinase (AMPK) subfamilies. Interestingly, LKB1 plays a key role and is considered a master kinase within the CaMKL family. It has been shown that LKB1 signaling leads to atheroprotective effects, while, for example, members of the microtubule affinity-regulating kinase (MARK) subfamily have been described to aggravate atherosclerosis development. These observations highlight the importance of studying kinases and their signaling pathways in atherosclerosis, bringing us a step closer to unraveling the underlying mechanisms of atherosclerosis.

CTRP9 prevents atherosclerosis progression through changing autophagic status of macrophages by activating USP22 mediated-de-ubiquitination on Sirt1 in vitro

BACKGROUND

Atherosclerosis (AS) is commonly regarded as a key driver accounted for the leading causes of morbidity and mortality among cardiovascular and cerebrovascular diseases. A growing body of evidence indicates that autophagy in macrophages involved in AS might be a potential therapeutic target. C1q/TNF-related protein 9 (CTRP9) has been proven to delay the progression of cardiovascular diseases. However, the relations between CTRP9 and Sirt1, as well as their effects on macrophages autophagy have not been fully explored.

METHODS

Macrophages were differentiated from mononuclear cells collected from peripheral blood samples of healthy donors. The in vitro AS models were constructed by ox-LDL treatment. Cell viability was determined by CCK-8 assay. Immunofluorescence assay of LC3 was implemented for evaluating autophagy activity. Oil Red O staining was performed for lipid accumulation detection. ELISA, cholesterol concentration assay and cholesterol efflux analysis were conducted using commercial kits. Cycloheximide assay was implemented for revealing protein stability. RT-qPCR was used for mRNA expression detection, and western blotting was performed for protein level monitoring.

RESULTS

CTRP9 attenuated impaired cell viability, autophagy inhibition and increased lipid accumulation induced by ox-LDL. Moreover, CTRP9 maintained Sirt1 protein level through enhancing its stability through de-ubiquitination, which was mediated by upregulated USP22 level. CRTP9 exerted its protective role in promoting autophagy and reducing lipid accumulation through the USP22/Sirt1 axis.

CONCLUSION

Collectively, CTRP9 alleviates lipid accumulation and facilitated the macrophages autophagy by upregulating USP22 level and maintaining Sirt1 protein expression, thereby exerting a protective role in AS progression in vitro.

C1q/Tumor Necrosis Factor-Related Protein-9 Enhances Macrophage Cholesterol Efflux and Improves Reverse Cholesterol Transport via AMPK Activation

Cholesterol efflux from foam cells in atherosclerotic plaques is crucial for reverse cholesterol transport (RCT), an important antiatherogenic event. ATP-binding cassette (ABC) transporters, ABCA1 and ABCG1, are key receptors in the cholesterol efflux pathway. C1q/tumor necrosis factor-related protein-9 (CTRP9) is a newly discovered adipokine and exhibits an atheroprotective activity. However, the role of CTRP9 in RCT still remains unknown. In this work, we investigated the effect of subcutaneous administration of CTRP9 protein on RCT and atherosclerotic lesion formation in ApoE-/- mice fed with a high-fat diet. CTRP9-dependent regulation of cholesterol efflux and ABC transporters in RAW 264.7 foam cells was determined. Our results showed that CTRP9 protein decreased atherosclerotic lesions, increased cholesterol efflux, and upregulated liver ABCA1 and ABCG1 expression in ApoE-/- mice. CTRP9 treatment dose-dependently increased mRNA and protein expression of ABCA1, ABCG1, and LXR-α in RAW 264.7 foam cells. Moreover, the expression and phosphorylation of AMPK was potentiated upon CTRP9 treatment. Notably, CTRP9-induced cholesterol efflux and upregulation of ABCA, ABCG1, and LXR-α were impaired when AMPK was knocked down. AMPK depletion restored cholesterol accumulation in CTRP9-treated RAW 264.7 cells. Taken together, subcutaneous injection is an effective novel delivery route for CTRP9 protein, and exogenous CTRP9 can facilitate cholesterol efflux and promote RCT in an animal model of atherosclerosis. The atheroprotective activity of CTRP9 is mediated through the activation of AMPK signaling.

CTRP family in diseases associated with inflammation and metabolism: molecular mechanisms and clinical implication

C1q/tumor necrosis factor (TNF) related proteins (CTRPs) is a newly discovered adipokine family with conservative structure and ubiquitous distribution and is secreted by adipose tissues. Recently, CTRPs have attracted increasing attention due to the its wide-ranging effects upon inflammation and metabolism. To-date, 15 members of CTRPs (CTRP1-15) with the characteristic C1q domain have been characterized. Earlier in-depth phenotypic analyses of mouse models of CTRPs deficiency have also unveiled ample function of CTRPs in inflammation and metabolism. This review focuses on the rise of CTRPs, with a special emphasis on the latest discoveries with regards to the effects of the CTRP family on inflammation and metabolism as well as related diseases. We first introduced the structure of characteristic domain and polymerization of CTRPs to reveal its pleiotropic biological functions. Next, intimate association of CTRP family with inflammation and metabolism, as well as the involvement of CTRPs as nodes in complex molecular networks, were elaborated. With expanding membership of CTRP family, the information presented here provides new perspectives for therapeutic strategies to improve inflammatory and metabolic abnormalities.

Global trends and Frontier topics about vascular smooth muscle cells phenotype switch: A bibliometric analysis from 1999 to 2021

Objective: Vascular smooth muscle cell phenotype switch (VSMCPS) plays a significant role in vascular remodeling. This study aimed to conduct a bibliometric analysis and visualize the knowledge map of research on VSMCPS. Methods: We retrieved publications focusing on VSMCPS from the Web of Science Core Collection database (SCI-EXPANDED) from 1999 to 2021. Using bibliometric tools, VOSviewer and CiteSpace, we identified the most productive researchers, journals, institutions, and countries. At the same time, the trends, hot topics, and knowledge networks were analyzed and visualized. Results: A total of 2213 publications were included in this analysis. The number of annual publications in the VSMCPS field exhibited an upward trend and could be roughly divided into three phases. Until 2006, the most prolific authors were from the United States. As of 2008, the number of articles published in China increased dramatically to reach 126 papers in 2020. As of 2014, China was the most productive country in this field. The United States ranked first in the number of highly-influential authors, institutions, and literature from 1999 to 2022. Owens GK, Hata, Akiko, and Wen, jin-kun were the most prolific authors. Arteriosclerosis Thrombosis and Vascular Biology, Circulation Research, and Cardiovascular Research were the top-ranked journals in this field. "Vascular remodeling," "atherosclerosis," "neointima," "hypertension", and "inflammation" were the main researched topics. New diseases, new mechanisms, and new phenotype (e.g., micro RNA, macrophage-like-cell, hypoxia, autophagy, long noncoding RNA, oxidative stress, endoplasmic reticulum stress, senescence, aging, abdominal aortic aneurysm, and aortic dissection) represent the trending topics in recent years. Conclusion: This study systematically analyzed and visualized the knowledge map of VSMCPS over the past 2 decades. Our findings provide a comprehensive overview for scholars who want to understand current trends and new research frontiers in this area.

BMAL1 modulates smooth muscle cells phenotypic switch towards fibroblast-like cells and stabilizes atherosclerotic plaques by upregulating YAP1

BACKGROUND

Ischemic heart diseases and ischemic stroke are closely related to circadian clock and unstable atherosclerotic plaques. Vascular smooth muscle cells (VSMCs) can stabilize or destabilize an atherosclerotic lesion through phenotypic switch. BMAL1 is not only an indispensable core component in circadian clock but also an important regulator in atherosclerosis and VSMCs proliferation. However, little is known about the modulation mechanisms of BMAL1 in VSMCs phenotypic switch and atherosclerotic plaque stability.

METHODS

We integrated histological analysis of human plaques, in vivo experiments of VSMC-specific Bmal1-/- mice, in vitro experiments, and gene set enrichment analysis (GSEA) of public datasets of human plaques to explore the function of BMAL1 in VSMCs phonotypic switch and plaque stability.

FINDINGS

Comparing to human unstable plaques, BMAL1 was higher in stable plaques, accompanied by elevated YAP1 and fibroblast maker FSP1 which were positively correlated with BMAL1. In response to Methyl-β-cyclodextrin-cholesterol, oxidized-low-density-lipoprotein and platelet-derived-growth-factor-BB, VSMCs embarked on phenotypic switch and upregulated BMAL, YAP1 and FSP1. Besides, BMAL1 overexpression promoted VSMCs phonotypic switch towards fibroblast-like cells by transcriptionally upregulating the expression of YAP1. BMAL1 or YAP1 knock-down inhibited VSMCs phonotypic switch and downregulated FSP1. Furthermore, VSMC-specific Bmal1-/- mice exhibited VSMCs with lower YAP1 and FSP1 levels, and more vulnerable plaques with less collagen content. In addition, BMAL1 suppressed the migration of VSMCs. The GSEA results of public datasets were consistent with our laboratory findings.

INTERPRETATION

Our results highlight the importance of BMAL1 as a major regulator in VSMCs phenotypic switch towards fibroblast-like cells which stabilize an atherosclerotic plaque.

Putative therapeutic impacts of cardiac CTRP9 in ischaemia/reperfusion injury

Recently, cytokines belonging to C1q/tumour necrosis factor‐related proteins (CTRPs) superfamily have attracted increasing attention due to multiple metabolic functions and desirable anti‐inflammatory effects. These various molecular effectors exhibit key roles upon the onset of cardiovascular diseases, making them novel adipo/cardiokines. This review article aimed to highlight recent findings correlated with therapeutic effects and additional mechanisms specific to the CTRP9, particularly in cardiac ischaemia/reperfusion injury (IRI). Besides, the network of the CTPR9 signalling pathway and its possible relationship with IRI were discussed. Together, the discovery of all involved underlying mechanisms could shed light to alleviate the pathological sequelae after the occurrence of IRI.

Adipokines, adiposity, and atherosclerosis

Characterized by a surplus of whole-body adiposity, obesity is strongly associated with the prognosis of atherosclerosis, a hallmark of coronary artery disease (CAD) and the major contributor to cardiovascular disease (CVD) mortality. Adipose tissue serves a primary role as a lipid-storage organ, secreting cytokines known as adipokines that affect whole-body metabolism, inflammation, and endocrine functions. Emerging evidence suggests that adipokines can play important roles in atherosclerosis development, progression, as well as regression. Here, we review the versatile functions of various adipokines in atherosclerosis and divide these respective functions into three major groups: protective, deteriorative, and undefined. The protective adipokines represented here are adiponectin, fibroblast growth factor 21 (FGF-21), C1q tumor necrosis factor-related protein 9 (CTRP9), and progranulin, while the deteriorative adipokines listed include leptin, chemerin, resistin, Interleukin- 6 (IL-6), and more, with additional adipokines that have unclear roles denoted as undefined adipokines. Comprehensively categorizing adipokines in the context of atherosclerosis can help elucidate the various pathways involved and potentially pave novel therapeutic approaches to treat CVDs.

C1q/Tumor Necrosis Factor-Related Protein 9: Basics and Therapeutic Potentials

C1q/tumor necrosis factor-related protein 9 (CTRP9) is a newly discovered adipokine that is the closest paralog of adiponectin. Proteolytic cleavage of CTRP9 leads to the release of the globular domain (gCTRP9), which serves as the major circulating subtype. After binding with adiponectin receptor 1 (AdipoR1) and N-cadherin, CTRP9 activates various signaling pathways to regulate glucose and lipid metabolism, vasodilation and cell differentiation. Throughout human development and adult life, CTRP9 controls many biological phenomena. simultaneously, abnormal gene or protein expression of CTRP9 is accompanied by a wide range of human pathological phenomena. In this review, we briefly introduce CTRP9 and its associated signaling pathways and physiological functions, which may be helpful in the understanding of the occurrence of diseases. Moreover, we summarize the broader research prospects of CTRP9 and advances in therapeutic intervention. In recent years, CTRP9 has attracted extensive attention due to its role in the pathogenesis of various diseases, providing further avenues for its exploitation as a potential biomarker or therapeutic target.

Hydrogen sulfide: A new therapeutic target in vascular diseases

Hydrogen sulfide (H₂S) is one of most important gas transmitters. H₂S modulates many physiological and pathological processes such as inflammation, oxidative stress and cell apoptosis that play a critical role in vascular function. Recently, solid evidence show that H₂S is closely associated to various vascular diseases. However, specific function of H₂S remains unclear. Therefore, in this review we systemically summarized the role of H₂S in vascular diseases, including hypertension, atherosclerosis, inflammation and angiogenesis. In addition, this review also outlined a novel therapeutic perspective comprising crosstalk between H₂S and smooth muscle cell function. Therefore, this review may provide new insight inH₂S application clinically.

The Role of Anti-Inflammatory Adipokines in Cardiometabolic Disorders: Moving beyond Adiponectin

The global burden of obesity has multiplied owing to its rapidly growing prevalence and obesity-related morbidity and mortality. In addition to the classic role of depositing extra energy, adipose tissue actively interferes with the metabolic balance by means of secreting bioactive compounds called adipokines. While most adipokines give rise to inflammatory conditions, the others with anti-inflammatory properties have been the novel focus of attention for the amelioration of cardiometabolic complications. This review compiles the current evidence on the roles of anti-inflammatory adipokines, namely, adiponectin, vaspin, the C1q/TNF-related protein (CTRP) family, secreted frizzled-related protein 5 (SFRP5), and omentin-1 on cardiometabolic health. Further investigations on the mechanism of action and prospective human trials may pave the way to their clinical application as innovative biomarkers and therapeutic targets for cardiovascular and metabolic disorders.

C1q/TNF-Related Protein 9 Attenuates Atherosclerosis by Inhibiting Hyperglycemia-Induced Endothelial Cell Senescence Through the AMPKα/KLF4 Signaling Pathway

Hyperglycemia-induced endothelial cell senescence has been widely reported to be involved in the pathogenesis of type 2 diabetes mellitus‒accelerated atherosclerosis. Thus, understanding the underlying mechanisms and identifying potential therapeutic targets for endothelial cell senescence are valuable for attenuating atherosclerosis progression. C1q/tumor necrosis factor-related protein 9 (CTRP9), an emerging potential cardiokine, exerts a significant protective effect with respect to atherosclerosis, particularly in endothelial cells. However, the exact mechanism by which CTRP9 prevents endothelial cells from hyperglycemia-induced senescence remains unclear. This study aimed to investigate the effects of CTRP9 on hyperglycemia-induced endothelial cell senescence and atherosclerotic plaque formation in diabetic apolipoprotein E knockout (ApoE KO) mice. Human umbilical vein endothelial cells (HUVECs) were cultured in normal glucose (5.5 mM) and high glucose (40 mM) with or without recombinant human CTRP9 protein (3 μg/ml) for 48 h. Purified lentiviruses overexpressing CTRP9 (Lv-CTRP9) and control vectors containing green fluorescent protein (Lv-GFP) were injected via the tail vein into streptozotocin-induced diabetic ApoE KO mice. Results revealed that exposure of HUVECs to HG significantly increased the expression of Krüppel-like factor 4 (KLF4) and cyclin-dependent kinase inhibitor p21 (p21) and decreased that of telomerase reverse transcriptase (TERT). Treatment with recombinant human CTRP9 protein protected HUVECs from HG-induced premature senescence and dysfunction. CTRP9 promoted the phosphorylation of AMP-activated kinase (AMPK), attenuated the expression of KLF4 and p21 induced by HG, and increased the expression of TERT in HUVECs. Furthermore, in the background of AMPKα knockdown or KLF4 activation, the protective effects of CTRP9 were abolished. In-vivo experiments showed that the overexpression of CTRP9 inhibited vascular senescence and reduced atherosclerotic plaque formation in ApoE KO mice with diabetes. In conclusion, we demonstrate that KLF4 upregulation plays a crucial role in HG-induced endothelial senescence. This anti-atherosclerotic effect of CTRP9 may be partly attributed to the inhibition of HG-induced endothelial senescence through an AMPKα/KLF4-dependent mechanism, suggesting that CTRP9 could benefit further therapeutic approaches for type 2 diabetes mellitus‒accelerated atherosclerosis.

C1q/TNF-related protein 9 decreases cardiomyocyte hypoxia/reoxygenation-induced inflammation by inhibiting the TLR4/MyD88/NF-κB signaling pathway

C1q/TNF-related protein 9 (CTRP9) acts as an adipokine and has been reported to exert numerous biological functions, such as anti-inflammatory and anti-oxidative stress effects, in ischemic heart disease. In the present study, the role of CTRP9 in neonatal rat cardiomyocytes (NRCMs) following hypoxia/reoxygenation (H/R) and the underlying mechanism was investigated. Adenoviral vectors containing CTRP9 or green fluorescent protein were transfected into NRCMs. A H/R model was constructed 2 days after transfection by 2 h incubation under hypoxia followed by 4 h of reoxygenation. Lactate dehydrogenase (LDH), creatine kinase (CK) and CK-myocardial band (CK-MB) levels were detected by a biochemical analyzer using biochemical kits. In addition, cell viability was detected using trypan blue staining to determine the extent of cell injury. Inflammatory cytokines TNF-α, IL-6 and IL-10 were measured by ELISA. Western blotting and reverse transcription-quantitative PCR were used to evaluate the expression levels of CTRP9, toll-like receptor 4 (TLR4), myeloid differentiation primary response (MyD88) and NF-κB. The DNA binding activity of NF-κB was also detected using an electrophoretic mobility shift assay. The results indicated that transfection with adenoviral vectors containing CTRP9 could markedly enhance CTRP9 expression. CTRP9 overexpression increased cell viability and decreased the release of LDH, CK and CK-MB. In addition, CTRP9 overexpression reduced TNF-α and IL-6 levels whilst increasing IL-10 levels, but decreased the expression of TLR4, MyD88 and NF-κB. Furthermore, the DNA binding activity of NF-κB under H/R was also decreased by CTRP9 overexpression. In conclusion, the results of the present study suggested that CTRP9 could protect cardiomyocytes from H/R injury, which was at least partially due to the inhibition of the TLR4/MyD88/NF-κB signaling pathway to reduce the release of inflammatory cytokines.

Metformin inhibits cholesterol‑induced adhesion molecule expression via activating the AMPK signaling pathway in vascular smooth muscle cells

Recruitment of lymphocytes to the vascular wall contributes to the pathogenesis of atherosclerosis (AS). The expression of cellular adhesion molecules, such as vascular cell adhesion molecule-1 and intercellular adhesion molecule-1, serves a critical role in mediating lymphocyte adhesion to the vascular wall. Cholesterol loading induces the expression of adhesion molecules in vascular smooth muscle cells (VSMCs), but the underlying mechanism is not completely understood. The present study aimed to investigate the mechanism underlying the effects of cholesterol on adhesion molecule expression, and whether metformin protected VSMCs against cholesterol-induced functional alterations. Human VSMCs were loaded with cholesterol and different concentrations of metformin. The expression levels of adhesion molecules were assessed via reverse transcription-quantitative PCR and western blotting. Reactive oxygen species (ROS) accumulation and levels were quantified via fluorescence assays and spectrophotometry, respectively. AMP-activated protein kinase (AMPK), p38 MAPK and NF-κB signaling pathway-related protein expression levels were evaluated via western blotting. Compared with the control group, cholesterol loading significantly upregulated adhesion molecule expression levels on VSMCs by increasing intracellular ROS levels and activating the p38 MAPK and NF-κB signaling pathways. Metformin decreased cholesterol-induced VSMC damage by activating the AMPK signaling pathway, and suppressing p38 MAPK and NF-κB signaling. The present study indicated the therapeutic potential of metformin for VSMC protection, reduction of monocyte adhesion, and ultimately, the prevention and treatment of AS.

C1q/TNF-related Protein 9 Inhibits High Glucose-Induced Oxidative Stress and Apoptosis in Retinal Pigment Epithelial Cells Through the Activation of AMPK/Nrf2 Signaling Pathway

Diabetic retinopathy (DR) is one of the common complications of diabetes mellitus. C1q/TNF-related protein 9 (CTRP9) has been demonstrated to be associated with the progression of diabetes and relative complications. However, its role in DR and underlying action of mechanism are not yet well understood. In the present study, human retinal pigment epithelial ARPE-19 cells were cultured under high concentration of glucose to simulate hyperglycemia condition in vitro. Our results showed that the expression of CTRP9 was significantly decreased in high glucose (HG)–stimulated ARPE-19 cells. CTRP9 overexpression improved HG-caused reduction in cell viability of ARPE-19 cells. CTRP9 overexpression significantly attenuated HG-induced oxidative stress, as proved by decreased levels of reactive oxygen species and malondialdehyde, and increased superoxide dismutase activity. Moreover, CTRP9 also prevented apoptosis in ARPE-19 cells in response to HG stimulation with decreased caspse-3 activity and bax expression, as well as increased bcl-2 expression. In contrast, knockdown of CTRP9 aggravated HG-induced oxidative stress and apoptosis. Furthermore, CTRP9 significantly induced the activation of AMPK/Nrf2 pathway in HG-induced ARPE-19 cells. Notably, inhibiting AMPK or Nrf2 blocked the protective effect of CTRP9 on ARPE-19 cells exposed to HG stimulation. Taken together, our findings suggested a protective effect of CTRP9 on HG-induced ARPE-19 cells and a putative mechanism involving the activation of AMPK/Nrf2 signaling pathway.

Substrate Stiffness Regulates Cholesterol Efflux in Smooth Muscle Cells

The infiltration and deposition of cholesterol in the arterial wall play an important role in the initiation and development of atherosclerosis. Smooth muscle cells (SMCs) are the major cell type in the intima. Upon exposure to cholesterol, SMCs may undergo a phenotype switching into foam cells. Meanwhile, the pathological processes of the blood vessel such as cholesterol deposition and calcification induce the changes in the substrate stiffness around SMCs. However, whether substrate stiffness affects the cholesterol accumulation in SMCs and the formation of foam cells is not well-understood. In this study, SMCs were cultured on the substrates with different stiffnesses ranging from 1 to 100 kPa and treated with cholesterol. We found that cholesterol accumulation in SMCs was higher on 1 and 100 kPa substrates than that on intermediate stiffness at 40 kPa; consistently, total cholesterol (TC) content on 1 and 100 kPa substrates was also higher. As a result, the accumulation of cholesterol increased the expression of macrophage marker CD68 and downregulated SMC contractile marker smooth muscle α-actin (ACTA2). Furthermore, the mRNA and protein expression level of cholesterol efflux gene ATP-binding cassette transporter A1 (ABCA1) was much higher on 40 kPa substrate. With the treatment of a liver X receptor (LXR) agonist GW3965, the expression of ABCA1 increased and cholesterol loading decreased, showing an additive effect with substrate stiffness. In contrast, inhibition of LXR decreased ABCA1 gene expression and increased cholesterol accumulation in SMCs. Consistently, when ABCA1 gene was knockdown, the cholesterol accumulation was increased in SMCs on all substrates with different stiffness. These results revealed that substrate stiffness played an important role on SMCs cholesterol accumulation by regulating the ABCA1 expression. Our findings on the effects of substrate stiffness on cholesterol efflux unravel a new mechanism of biophysical regulation of cholesterol metabolism and SMC phenotype, and provide a rational basis for the development of novel therapies.

CTRP9 Enhances Efferocytosis in Macrophages via MAPK/Drp1-Mediated Mitochondrial Fission and AdipoR1-Induced Immunometabolism

Background

Clearance of apoptotic cells (ACs) by phagocytes (efferocytosis) suppresses post-apoptotic necrosis and alleviates inflammation. Defective efferocytosis induces diseases that include atherosclerosis and autoimmune diseases. C1q/TNF-related protein 9 (CTRP9), a novel adipokine, has been reported to protect against various cardiovascular disease; however, the effect of CTRP9 on efferocytosis has not been elucidated.

Methods

1. The efferocytosis of macrophages incubated with ACs with or without CTRP9 treatment was detected by flow cytometry (FCM) and immunostaining. The unengulfed ACs of CTRP9-KO and wild-type (WT) mice after dexamethasone injection were detected by TUNEL assay. 2. As mitochondrial fission is important for promoting efferocytosis, the effect of CTRP9 on mitochondrial fission was measured by fission/fusion-related proteins (MFN2, DRP1, MFF, and OPA1) and visualized by staining with MitoTracker. 3. On account of metabolism insults in engulfed macrophages, we conducted a two-stage efferocytosis assay, and the protective effects of CTRP9 on metabolism were investigated by Western blot.

Results

CTRP9 significantly facilitated macrophage efferocytosis, and it promoted mitochondrial fission by increasing the expression of p-DRP1 (s616) and the translocation of DRP1 from the cytoplasm to the mitochondria. The p38/Jnk-MAPK pathway was activated after treatment with 1 μg/mL CTRP9. When we blocked the activation of MAPK signaling by SB203580 and SP600125, the mediated effect on p-DRP1 (s616) was reduced. Moreover, CTRP9 increased the levels of ABCA1, PPAR-y, HIF-1a and GLUT1, as well as the release of lactate in basal and engulfed macrophages, which revealed that the metabolism of macrophages was advanced. Apoptotic cell-conditioned media (ACCM) and ACs increased the expression of adiponectin receptor 1 (AdipoR1). Down-regulation of AdipoR1 by siRNA could abrogate the immunometabolism effects of CTRP9.

Conclusion

CTRP9 promoted efferocytosis in macrophages via MAPK/drp1-mediated mitochondrial fission and AdipoR1-induced immunometabolism.

CTRP9 alleviates foam cells apoptosis by enhancing cholesterol efflux

The apoptosis of foam cells leads to instability of atherosclerotic plaques. This study was designed to explore the protective role of CTRP9 in foam cell apoptosis. In our experiment, CTRP9 alleviated foam cell apoptosis. Meanwhile, CTRP9 upregulated the expression of proteins important for cholesterol efflux, such as LXRα, CYP27A1, ABCG1 and ABCA1, and improved cholesterol efflux in foam cells. Moreover, CTRP9 inhibited Wnt3a and β-catenin expression and β-catenin nuclear translocation in foam cells. In addition, adenovirus overexpression of Wnt3a abolished the effect of CTRP9 on macrophage apoptosis. Mechanistically, the AMPK inhibitor abolished the effect of CTRP9 on foam cell apoptosis, and downregulation of AdipoR1 by siRNA abrogated the activation of AMPK and the effect of CTRP9 on foam cell apoptosis. We concluded that CTRP9 achieved these protective effects on foam cells through the AdipoR1/AMPK pathway.

Prostacyclin facilitates vascular smooth muscle cell phenotypic transformation via activating TP receptors when IP receptors are deficient

AIM

By activating prostacyclin receptors (IP receptors), prostacyclin (PGI₂ ) exerts cardiovascular protective effects such as vasodilation and inhibition of vascular smooth muscle cell (VSMC) proliferation. However, IP receptors are dysfunctional under pathological conditions, and PGI₂ produces detrimental effects that are opposite to its physiological protective effects via thromboxane-prostanoid (TP) receptors. This attempted to investigate whether or not IP receptor dysfunction facilitates the shift of PGI₂ action.

METHODS

The effects of PGI₂ and its stable analog iloprost on VSMC phenotypic transformation and proliferation were examined in A10 cells silencing IP receptors, in human aortic VSMCs (HAVSMCs) knocked down IP receptor by CRISPR-Cas9, or in HAVSMCs transfected with a dysfunctional mutation of IP receptor IP^R212C .

RESULTS

PGI₂ /iloprost treatment stimulated cell proliferation, upregulated synthetic proteins and downregulated contractile proteins, suggesting that PGI₂ /iloprost promotes VSMC phenotypic transformation in IP-deficient cells. The effect of PGI₂ /iloprost was prevented by TP antagonist S18886 or TP knockdown, indicating that the VSMC detrimental effect of PGI₂ is dependent on TP receptor. RNA sequencing and Western blotting results showed that RhoA/ROCKs, MEK1/2 and JNK signalling cascades were involved. Moreover, IP deficiency increased the distribution of TP receptors at the cell membrane.

CONCLUSION

PGI₂ induces VSMC phenotypic transformation when IP receptors are impaired. This is attributed to the activation of TP receptor and its downstream signaling cascades, and to the increased membrane distribution of TP receptors. The VSMC detrimental effect of PGI₂ medicated by IP dysfunction and TP activation might probably exacerbate vascular remodelling, accelerating cardiovascular diseases.

Nϵ-Carboxymethyl-Lysine Deteriorates Vascular Calcification in Diabetic Atherosclerosis Induced by Vascular Smooth Muscle Cell-Derived Foam Cells

Nϵ-carboxymethyl-lysine (CML), an advanced glycation end product, is involved in vascular calcification (VC) in diabetic atherosclerosis. This study aimed to investigate the effects of CML on VC in diabetic atherosclerosis induced by vascular smooth muscle cell (VSMC)–derived foam cells. Human studies, animal studies and cell studies were performed. The human study results from 100 patients revealed a poor blood glucose and lipid status and more severe coronary lesions and stenosis in patients with coronary artery disease and diabetes mellitus. Intraperitoneal injection of streptozotocin combined with a high-fat diet was used to build a diabetic atherosclerosis model in ApoE^−/− mice. The animal study results indicated that CML accelerated VC progression in diabetic atherosclerosis by accelerating the accumulation of VSMC-derived foam cells in ApoE^−/− mice. The cell study results illustrated that CML induced VSMC-derived foam cells apoptosis and aggravated foam cells calcification. Consistent with this finding, calcium content and the expression levels of alkaline phosphatase, bone morphogenetic protein 2 and runt-related transcription factor 2 were significantly elevated in A7r5 cells treated with oxidation-low-density lipoprotein and CML. Thus, we concluded that CML promoted VSMC-derived foam cells calcification to aggravate VC in diabetic atherosclerosis, providing evidence for the contribution of foam cells to diabetic VC.

Circulating CTRP9 correlates with the prevention of aortic calcification in renal allograft recipients

Background

Cardiovascular disease (CVD) due to atherosclerosis is a major cause of death in renal allograft recipients. Recently, C1q/TNF-α related protein-9 (CTRP9), which is a paralog of adiponectin (ADPN), has been suggested to be related to the prevention of atherosclerosis and the occurrence of CVD, but this relationship has not been confirmed in renal allograft recipients.

Subjects and methods

The relationships among the serum CTRP9 concentration, serum ADPN concentration, and vascular calcification were investigated in 50 kidney transplantation recipients at our hospital. Calcification of the abdominal aorta was evaluated according to the aortic calcification area index (ACAI) calculated from CT images. Changes in the serum CTRP9 and ADPN fractions and ACAI were examined for 8 years. In addition, the expression of CTRP9 and ADPN and their respective receptors AdipoR1 and R2 in muscular arteries of the kidney was examined by immunofluorescence.

Results

In renal allograft recipients, the serum CTRP9 concentration at the start of the observation was not significant correlated with eGFR or serum high-molecular-weight (HMW)-ADPN concentration (rS = -0.009, p = 0.950; rS = -0.226, p = 0.114, respectively). However, the change in the serum CTRP9 concentration was positively correlated with the change in the serum HMW-ADPN concentration (rS = 0.315, p = 0.026) and negatively correlated with the change in ACAI (rS = -0.367, p = 0.009). Multiple regression analysis revealed that the serum HMW-ADPN concentration was a significant positive factor for the change in the serum CTRP9 concentration. Moreover, for ACAI, an increase in the serum CTRP9 concentration was an improving factor, but aging was an exacerbating factor. Furthermore, colocalization of CTRP9 and AdipoR1 was noted in the luminal side of intra-renal arterial intima.

Conclusion

In renal allograft recipients, both CTRP9 and HMW-ADPN were suggested to prevent the progression of aortic calcification through AdipoR1.

CTRP9 Ameliorates Atrial Inflammation, Fibrosis, and Vulnerability to Atrial Fibrillation in Post-Myocardial Infarction Rats

Background

Inflammation and fibrosis play an important role in the pathogenesis of atrial fibrillation (AF) after myocardial infarction (MI). CTRP9 (C1q/tumor necrosis factor‐related protein‐9) as a secreted glycoprotein can reverse left ventricle remodeling post‐MI, but its effects on MI‐induced atrial inflammation, fibrosis, and associated AF are unknown.

Methods and Results

MI model rats received adenoviral supplementation of CTRP9 (Ad‐CTRP9) by jugular‐vein injection. Cardiac function, inflammatory, and fibrotic indexes and related signaling pathways, electrophysiological properties, and AF inducibility of atria in vivo and ex vivo were detected in 3 or 7 days after MI. shCTRP9 (short hairpin CTRP9) and shRNA were injected into rat and performed similar detection at day 5 or 10. Adverse atrial inflammation and fibrosis, cardiac dysfunction were induced in both MI and Ad‐GFP (adenovirus‐encoding green fluorescent protein)+MI rats. Systemic CTRP9 treatment improved cardiac dysfunction post‐MI. CTRP9 markedly ameliorated macrophage infiltration and attenuated the inflammatory responses by downregulating interleukin‐1β and interleukin‐6, and upregulating interleukin‐10, in 3 days post‐MI; depressed left atrial fibrosis by decreasing the expressions of collagen types I and III, α‐SMA, and transforming growth factor β1 in 7 days post‐MI possibly through depressing the Toll‐like receptor 4/nuclear factor‐κB and Smad2/3 signaling pathways. Electrophysiologic recordings showed that increased AF inducibility and duration, and prolongation of interatrial conduction time induced by MI were attenuated by CTRP9; moreover, CTRP9 was negatively correlated with interleukin‐1β and AF duration. Downregulation of CTRP9 aggravated atrial inflammation, fibrosis, susceptibility of AF and prolonged interatrial conduction time, without affecting cardiac function.

Conclusions

CTRP9 is effective at attenuating atrial inflammation and fibrosis, possibly via its inhibitory effects on the Toll‐like receptor 4/nuclear factor‐κB and Smad2/3 signaling pathways, and may be an original upstream therapy for AF in early phase of MI.

miR-124 regulates cerebromicrovascular function in APP/PS1 transgenic mice via C1ql3

Many neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease, are associated with microvascular dysfunction, but the cellular and molecular mechanisms are poorly understood. Recently, microRNAs (miRNAs) have been suggested to be involved in the microvascular dysfunction and subsequent memory impairment. MicroRNA-124 (miR-124) is one of the most abundant miRNAs in the brain that is dysregulated in the hippocampus of AD animals. To explore the role of miR-124 in AD pathology, we employed the APP/PS1 transgenic mice and found downregulation of miR-124 and upregulation of complement C1q-like protein 3 (C1ql3) in the hippocampus and cerebral cortex. Downregulation of miR-124 expression resulted in Aβ deposition and a variety of cerebromicrovascular impairments, including the decline in microvascular density, reduced angiogenesis, accompanied by C1ql3 alteration. Treatment with lentivirus-mediated overexpression of miR-124 or the C1q inhibitor C1INH rescued breakdown of blood-brain barrier, promoted angiogenesis and reduced Aβ deposition, and finally alleviated learning and memory deficit in APP/PS1 mice. Moreover, we found that C1ql3, a component of the classical complement, might be a potential target of miR-124. These results suggested that miR-124 was involved in the angiogenesis and vascular integrity in the hippocampus and the cerebral cortex of the AD mice by regulating the classical complement C1ql3.

C1q/TNF-Related Protein 9 Inhibits THP-1 Macrophage Foam Cell Formation by Enhancing Autophagy

During the pathogenesis of early atherosclerosis, lipid-loaded macrophages are involved in plaque development and progression. As a novel adipokine, C1q/tumor necrosis factor–related protein-9 (CTRP9) has beneficial effects in cardiovascular disease. However, previous reports have not studied whether the formation of macrophage foam cell induced by oxidized low-density lipoprotein (ox-LDL) is affected by CTRP9. According to our study, in ox-LDL–induced THP-1 macrophages, CTRP9 could reduce the quantity of lipid droplets, lower the level of cholesteryl ester (CE), promote cholesterol efflux, as well as increase the expression level of the cholesterol transport receptors ATP-binding membrane cassette transporter A1 (ABCA1) and G1 (ABCG1). In addition, the protein of LC3 II is elevated and that of p62 is decreased in CTRP9-treated foam cells by enhancing autophagy. However, using 3-methyladenine (3-MA) abolished the role of CTRP9 by inhibiting autophagy. Mechanistically, the autophagy-promoting effects of CTRP9 on foam cells was reversed by an AMPK inhibitor, Compound C, which inhibited the signaling pathway of adenosine 5′-monophosphate (AMP)-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR). These results show that CTRP9 protects against atherosclerosis by promoting cholesterol efflux to reduce the formation of foam cell in virtue of inducing autophagy in an AMPK/mTOR signaling pathway–dependent manner.

C1q/TNF-related protein-9 promotes macrophage polarization and improves cardiac dysfunction after myocardial infarction

The timely regulation of inflammatory M1 macrophage polarization toward regenerative M2 macrophages suggests the possibility of immunotherapy after myocardial infarction (MI). C1q/TNF‐related protein‐9 (CTRP9) has anti‐inflammatory effects and can ameliorate heart function in mice after long‐term myocardial infarction. The role of CTRP9 in macrophage polarization remains completely unclear. This study determined whether CTRP9 can preserve post‐MI early cardiac function through the regulation of macrophage polarization. In the present study, an adenovirus‐delivered CTRP9 supplement promoted macrophage polarization at Day 3 post MI and improved cardiac function at Day 7 post MI. Pretreatment with gCTRP9 promoted the M1 to M2 polarization transition and attenuated inflammation after lipopolysaccharide + interferon‐γ stimulation; the effects were partly abrogated by the adenosine monophosphate kinase (AMPK) inhibitor compound C and were obviously reinforced by pyrrolidine dithiocarbamate, a nuclear factor‐κB (NF‐κB) inhibitor. Meanwhile, CTPR9 markedly reduced the expression of toll‐like receptor 4 (TLR4), myeloid differentiation factor 88 (MyD88), and NF‐κB p65 phosphorylation by promoting AMPK phosphorylation in vivo and in vitro. Moreover, the competitive binding of gCTRP9 and LPS to the myeloid differentiation protein 2 (MD2)/TLR4 complex was associated with direct binding to MD2, thereby inhibiting the downstream signaling molecule MyD88. Taken together, we demonstrated that CTRP9 improved post‐MI early cardiac function, at least in part, by modulating M1/M2 macrophage polarization, largely via the TLR4/MD2/MyD88 and AMPK‐NF‐κB pathways.

Cardiac-derived CTRP9 protects against myocardial ischemia/reperfusion injury via calreticulin-dependent inhibition of apoptosis

Cardiokines play an essential role in maintaining normal cardiac functions and responding to acute myocardial injury. Studies have demonstrated the heart itself is a significant source of C1q/TNF-related protein 9 (CTRP9). However, the biological role of cardiac-derived CTRP9 remains unclear. We hypothesize cardiac-derived CTRP9 responds to acute myocardial ischemia/reperfusion (MI/R) injury as a cardiokine. We explored the role of cardiac-derived CTRP9 in MI/R injury via genetic manipulation and a CTRP9-knockout (CTRP9-KO) animal model. Inhibition of cardiac CTRP9 exacerbated, whereas its overexpression ameliorated, left ventricular dysfunction and myocardial apoptosis. Endothelial CTRP9 expression was unchanged while cardiomyocyte CTRP9 levels decreased after simulated ischemia/`reperfusion (SI/R) in vitro. Cardiomyocyte CTRP9 overexpression inhibited SI/R-induced apoptosis, an effect abrogated by CTRP9 antibody. Mechanistically, cardiac-derived CTRP9 activated anti-apoptotic signaling pathways and inhibited endoplasmic reticulum (ER) stress-related apoptosis in MI/R injury. Notably, CTRP9 interacted with the ER molecular chaperone calreticulin (CRT) located on the cell surface and in the cytoplasm of cardiomyocytes. The CTRP9-CRT interaction activated the protein kinase A-cAMP response element binding protein (PKA-CREB) signaling pathway, blocked by functional neutralization of the autocrine CTRP9. Inhibition of either CRT or PKA blunted cardiac-derived CTRP9's anti-apoptotic actions against MI/R injury. We further confirmed these findings in CTRP9-KO rats. Together, these results demonstrate that autocrine CTRP9 of cardiomyocyte origin protects against MI/R injury via CRT association, activation of the PKA-CREB pathway, ultimately inhibiting cardiomyocyte apoptosis.

CTRP9 ameliorates cellular senescence via PGC‑1α/AMPK signaling in mesenchymal stem cells

Stroke is the second most common cause of death worldwide, and thus, it imposes great financial burdens on both individuals and society. Mesenchymal stem cell (MSC) therapy is a promising approach for ischemic brain injury. However, MSC treatment potential is progressively reduced with age, limiting their therapeutic efficacy for brain repair post‑stroke. C1q and tumor necrosis factor‑related protein 9 (CTRP9) is a novel cytoprotective cytokine with antioxidant effects, which is highly expressed in brain tissue. The present study tested the hypothesis that CTRP9 might act as an antisenescence factor to promote the rejuvenation of aged MSCs. MSCs were isolated from the bone marrow of young (8‑weeks‑old) and aged (18‑months‑old) male C57BL/6 mice. Cell proliferation was measured by Cell Counting Kit‑8 assay and cell viability was determined by MTT assay. Gene expression levels of interleukin (IL)‑6 and IL‑10 were evaluated with reverse transcription‑quantitative polymerase chain reaction, and secretion of vascular endothelial growth factor, basic fibroblast growth factor, hepatocyte growth factor, and insulin‑like growth factor were measured by ELISA. The expression levels of proteins in the peroxisome proliferator‑activated receptor γcoactivator (PGC)‑1α/AMP‑activated protein kinase (AMPK) signaling pathway were investigated with western blotting. Oxidative stress was evaluated by detecting mitochondrial membrane potential, reactive oxygen species, superoxide dismutase activity and malondialdehyde. MSCs isolated from aged mice exhibited reduced proliferation and viability, and impaired immunoregulatory and paracrine abilities, compared with MSCs from younger mice. CTRP9 had a significant antisenescence effect in aged MSCs by activating PGC‑1α/AMPK signaling and decreasing the oxidative response. Silencing either PGC‑1α or AMPK abolished the above effects of CTRP9. These results suggest that CTRP9 may have a critical role in cellular senescence by facilitating stem cell rejuvenation, and may therefore have the potential to enhance the efficacy of stem cell therapy.