Apelin and vascular endothelial growth factor are associated with mobilization of endothelial progenitor cells after acute myocardial infarction

Unraveling the Complex Molecular Interplay and Vascular Adaptive Changes in Hypertension-Induced Kidney Disease

Angiogenesis, the natural mechanism by which fresh blood vessels develop from preexisting ones, is altered in arterial hypertension (AH), impacting renal function. Studies have shown that hypertension-induced renal damage involves changes in capillary density (CD), indicating alterations in vascularization. We aimed to elucidate the role of the apelin receptor (APLNR), neuronal nitric oxide synthase (nNOS), and vascular endothelial growth factor (VEGF) in hypertension-induced renal damage. We used two groups of spontaneously hypertensive rats aged 6 and 12 months, representing different stages of AH, and compared them to age-matched normotensive controls. The kidney tissue samples were prepared through a well-established protocol. All data analysis was conducted with a dedicated software program. APLNR was localized in tubular epithelial cells and the endothelial cells of the glomeruli, with higher expression in older SHRs. The localization of nNOS and VEGF was similar. The expression of APLNR and nNOS increased with AH progression, while VEGF levels decreased. CD was lower in young SHRs compared to controls and decreased significantly in older SHRs in comparison to age-matched controls. Our statistical analysis revealed significant differences in molecule expression between age groups and varying correlations between the expression of the three molecules and CD.

Effects of Early Intensive Insulin Therapy on Endothelial Progenitor Cells in Patients with Newly Diagnosed Type 2 Diabetes

AIM

This study aimed to investigate the alteration of circulating CD34⁺KDR⁺CD133⁺ endothelial progenitor cells (EPCs) in patients with newly diagnosed type 2 diabetes and the mechanism of the effect of early intensive insulin therapy.

METHODS

In this study, 36 patients with newly diagnosed type 2 diabetes and 22 control subjects matched by age and gender were enrolled. All of the patients with diabetes received intensive insulin therapy. The number of EPCs was assessed by flow cytometry based on the expression of CD34, CD133, and kinase insert domain-containing receptor (KDR).

RESULTS

Levels of circulating CD34⁺KDR⁺CD133⁺ EPCs were higher in patients with diabetes compared to control subjects and significantly decreased after intensive insulin therapy. Levels of vascular endothelial growth factor (VEGF), a major contributor to EPC mobilization, were significantly higher in patients with diabetes compared to control subjects, and dramatically decreased after insulin therapy. Importantly, VEGF levels correlated with number of EPCs. Moreover, compared with control subjects, pro-inflammatory cytokines and oxidative stress were significantly higher in patients with diabetes and markedly decreased after intensive insulin therapy.

CONCLUSIONS

These results showed that type 2 diabetes is associated with an increase of circulating CD34⁺KDR⁺CD133⁺ EPCs at the onset of diabetes, indicating increased compensatory mobilization. Additionally, early intensive insulin therapy exerts a preserving effect on EPC level partly through improving inflammation status and oxidative stress, thereby implying a putative long-term beneficial effect on vascular integrity via suspending excessive EPC exhaustion.

CLINICAL TRIAL NUMBER

NCT03710811.

Apelin pathway in cardiovascular, kidney, and metabolic diseases: Therapeutic role of apelin analogs and apelin receptor agonists

The apelin/apelin receptor (ApelinR) signal transduction pathway exerts essential biological roles, particularly in the cardiovascular system. Disturbances in the apelin/ApelinR axis are linked to vascular, heart, kidney, and metabolic disorders. Therefore, the apelinergic system has surfaced as a critical therapeutic strategy for cardiovascular diseases (including pulmonary arterial hypertension), kidney disease, insulin resistance, hyponatremia, preeclampsia, and erectile dysfunction. However, apelin peptides are susceptible to rapid degradation through endogenous peptidases, limiting their use as therapeutic tools and translational potential. These proteases include angiotensin converting enzyme 2, neutral endopeptidase, and kallikrein thereby linking the apelin pathway with other peptide systems. In this context, apelin analogs with enhanced proteolytic stability and synthetic ApelinR agonists emerged as promising pharmacological alternatives. In this review, we focus on discussing the putative roles of the apelin pathway in various physiological systems from function to dysfunction, and emphasizing the therapeutic potential of newly generated metabolically stable apelin analogs and non-peptide ApelinR agonists.

TIR/BB-loop mimetic AS-1 protects vascular endothelial cells from injury induced by hypoxia/reoxygenation

Morphological and functional abnormalities of vascular endothelial cells (VECs) are risk factors of ischemia-reperfusion in skin flaps. Signaling pathway mediated by interleukin-1 receptor (IL-1R) is essential to hypoxia/reoxygenation (H/R) injury of VECs. While the TIR/BB-loop mimetic (AS-1) disrupts the interaction between IL-1R and myeloid differentiation primary-response protein 88 (MyD88), its role in the VECs dysfunction under H/R is unclear. In this study, we first showed that there was an infiltration of inflammatory cells and the apoptosis of VECs by using a skin flap section from patients who received flap transplantation. We then showed that the H/R treatment induced apoptosis and loss of cell migration of endothelial cell line H926 were attenuated by AS-1. Furthermore, our data suggested that AS-1 inhibits the interaction between IL-1R and MyD88, and subsequent phosphorylation of IκB and p38 pathway, as well as the nuclear localization of NF-KB subunit p65/p50. Thus, this study indicated that the protective role of AS-1 in H/R induced cellular injury may be due to the AS-1 mediated down-regulation of IL-1R signaling pathway.

Apelin and APJ orchestrate complex tissue-specific control of cardiomyocyte hypertrophy and contractility in the hypertrophy-heart failure transition

The G protein-coupled receptor APJ is a promising therapeutic target for heart failure. Constitutive deletion of APJ in the mouse is protective against the hypertrophy-heart failure transition via elimination of ligand-independent, β-arrestin-dependent stretch transduction. However, the cellular origin of this stretch transduction and the details of its interaction with apelin signaling remain unknown. We generated mice with conditional elimination of APJ in the endothelium (APJendo-/-) and myocardium (APJmyo-/-). No baseline difference was observed in left ventricular function in APJendo-/-, APJmyo-/-, or control (APJendo+/+, APJmyo+/+) mice. After exposure to transaortic constriction, APJendo-/- mice displayed decreased left ventricular systolic function and increased wall thickness, whereas APJmyo-/- mice were protected. At the cellular level, carbon fiber stretch of freshly isolated single cardiomyocytes demonstrated decreased contractile responses to stretch in APJ-/- cardiomyocytes compared with APJ+/+ cardiomyocytes. Ca2+ transients did not change with stretch in either APJ-/- or APJ+/+ cardiomyocytes. Application of apelin to APJ+/+ cardiomyocytes resulted in decreased Ca2+ transients. Furthermore, hearts of mice treated with apelin exhibited decreased phosphorylation in cardiac troponin I NH2-terminal residues (Ser22 and Ser23) consistent with increased Ca2+ sensitivity. These data establish that APJ stretch transduction is mediated specifically by myocardial APJ, that APJ is necessary for stretch-induced increases in contractility, and that apelin opposes APJ's stretch-mediated hypertrophy signaling by lowering Ca2+ transients while maintaining contractility through myofilament Ca2+ sensitization. These findings underscore apelin's unique potential as a therapeutic agent that can simultaneously support cardiac function and protect against the hypertrophy-heart failure transition. NEW & NOTEWORTHY These data address fundamental gaps in our understanding of apelin-APJ signaling in heart failure by localizing APJ's ligand-independent stretch sensing to the myocardium, identifying a novel mechanism of apelin-APJ inotropy via myofilament Ca2+ sensitization, and identifying potential mitigating effects of apelin in APJ stretch-induced hypertrophic signaling.

Trichosanthes pericarpium Aqueous Extract Enhances the Mobilization of Endothelial Progenitor Cells and Up-regulates the Expression of VEGF, eNOS, NO, and MMP-9 in Acute Myocardial Ischemic Rats

Trichosanthes pericarpium (TP) had been widely used to cure patients of cardiovascular disease for 2,000 years in China. This study aims to extend our previous work to explore the mechanism underlying the protective effect of TP on acute myocardial ischemia (AMI). We hypothesized that TP may display its protective effect on AMI by promoting the mobilization of endothelial progenitor cells (EPC) via up-regulating the expression level of vascular endothelial growth factor (VEGF), endothelial nitric oxide syntheses (eNOS), nitric oxide (NO), and matrix metalloproteinase 9 (MMP-9) in AMI rats. To confirm this hypothesis, we treated AMI model rats with intragastrical administration of TP aqueous extract (TPAE), and examined both changes in the number of CEPC, and the expression levels of VEGF, eNOS, NO, and MMP-9 in myocardial tissue and their plasma content in these rats. Rats in each group were randomly divided into seven subgroups. From day 1 to 7 following AMI modeling, rats in these subgroups was sequentially phlebotomized from their celiac artery after being anesthetized by chloral hydrate. We found that, compared with the AMI model rats, in rats treated by TPAE, the CEPC counts, the expression of VEGF, eNOS, NO, and MMP-9 in myocardial tissue and their plasma content all increased more rapidly 7 days after AMI and remained at higher level (P < 0.05 or P < 0.01). Our results showed that, in AMI rats, the TPAE could significantly promote the mobilization of EPC and up-regulate the expression level of VEGF, eNOS, NO, and MMP-9 in myocardium and their plasma content. Therefore, our results suggest that TAPE may regulate EPC mobilization through up-regulating the expression level of VEGF, eNOS, NO and MMP-9 in the myocardium of AMI rats.

Association of apelin and apelin receptor with the risk of coronary artery disease: a meta-analysis of observational studies

It is well established that apelin-APLNR (apelin receptor) pathway plays a central role in cardiovascular system. In this meta-analysis, we summarized published results on circulating apelin concentration in association with coronary artery disease (CAD), apelin and APLNR genetic polymorphism(s) in predisposition to CAD risk and circulating apelin changes after surgical treatment for CAD. The results from 15 articles were pooled. Two authors independently took charge of literature search, article selection and information collection. Overall, circulating apelin concentration was significantly lower in CAD patients (N=1021) than in controls (N=654) (weighted mean difference [WMD]: -1.285 ng/mL, 95% confidence interval [CI]: -1.790 to -0.780, P<0001), with significant heterogeneity (I²=99.3%) but without publication bias. For the association of APLNR gene rs9943582 polymorphism with CAD (patients/controls: 5975/4717), the mutant T allele was associated with a 5.2% increased risk relative to the wild C allele (odds ratio: 1.052, 95% CI: 0.990 to 1.117, P=0.100), without heterogeneity (I²=0.0%) or publication bias. Circulating apelin was increased significantly after surgical treatment for CAD (N=202) (WMD: 2.011 ng/mL, 95% CI: 0.541 to 3.481, P=0.007), with significant heterogeneity (I²=98.0%). Stratified analyses showed that circulating apelin was significantly reduced in studies with age- and sex-matched patients and controls (WMD: -1.881 ng/mL, 95% CI: -2.457 to -1.304, P<0.001) and with total sample size ≥125 (WMD: -1.657 ng/mL, 95% CI: -2.378 to -0.936, P<0.001), relative to studies without matching reports and with total sample size <125. In brief, our results suggested that circulating apelin was a prominent athero-protective marker against the development of CAD.

Hypoxia induces the proliferation of endothelial progenitor cells via upregulation of Apelin/APLNR/MAPK signaling

Endothelial progenitor cells (EPCs) can form new vessels through differentiation into endothelial cells (ECs), thus being important in the prevention of hypoxia/ischemia. Apelin can activate different signaling pathways through its receptor, APLNR, which regulate diverse biological functions, including cardiovascular function. However, the molecular mechanism by which Apelin mediates hypoxia-induced EPCs proliferation remain to be fully elucidated. The present study aimed to determine the role of Apelin/APLNR signaling in hypoxia-induced proliferation of EPCs. MTT assay was used to determine cell proliferation. Reverse transcription-quantitative polymerase chain reaction and western blotting analysis were conducted to examine mRNA and protein expression. It was revealed that hypoxia promoted the proliferation of the EPCs. Further investigation demonstrated that hypoxia promoted the expression levels of hypoxia-inducible factor (HIF)-1α, Apelin and APLNR in the EPCs. In addition, upregulation of Apelin or APLNR promoted the hypoxia-induced proliferation of the EPCs, while knockdown of Apelin or APLNR by small interfering RNA suppressed the hypoxia-induced proliferation of the EPCs, suggesting that the Apelin/APLNR axis is involved in hypoxia-induced proliferation of EPCs. Furthermore, pretreatment of the EPCs with SB-239063 or PD98059, two inhibitors of mitogen-activated protein kinase (MAPK), eliminated the Apelin upregulation-induced EPC proliferation, suggesting that MAPK signaling is a downstream effecter of Apelin/APLNR in EPCs. Therefore, the findings of the present study indicated that the production of HIF-1α, induced by hypoxia, activated the Apelin/APLNR and the downstream MAPK signaling pathways, leading to upregulated proliferation of the EPCs. These findings suggested that Apelin/APLNR signaling may be used as a potential therapeutic target for hypoxic/ischemic injury.

Apelin/APJ signaling promotes hypoxia-induced proliferation of endothelial progenitor cells via phosphoinositide-3 kinase/Akt signaling

Endothelial progenitor cells (EPCs) can adhere to the endothelium at sites of hypoxia/ischemia and participate in the formation of novel vessels through differentiating into endothelial cells (ECs). Apelin is an endogenous ligand for the G protein‑coupled receptor APJ, and apelin/APJ signaling has a role in cardiovascular function. The present study aimed to investigate the role of apelin/APJ signaling in the regulation of EPC proliferation under hypoxia. The results showed that hypoxia was able to induce EPC proliferation, accompanied with an upregulation of hypoxia‑inducible factor (HIF)‑1α as well as apelin/APJ signaling. Further investigation indicated that siRNA‑mediated knockdown of apelin or APJ expression attenuated the hypoxia‑induced proliferation of EPCs, suggesting that apelin/APJ signaling has an important role in hypoxia‑induced EPC proliferation. Moreover, the phosphoinositide‑3 kinase (PI3K)/Akt signaling pathway was found to be involved in the apelin/APJ‑mediated EPC proliferation under hypoxia. Based on these findings, the present study suggested that hypoxia‑induced upregulation of HIF‑1α promotes the expression of apelin and APJ, which further activate the downstream PI3K/Akt signaling pathway, a key promoter of EPC proliferation. In conclusion, the present study highlighted the role of apelin/APJ in the regulation of EPC proliferation, and apelin/APJ may therefore serve as a potential target for the prevention of hypoxic ischemic injury.

Adipokines, Vascular Wall, and Cardiovascular Disease

Epidemiological evidence has shown that abdominal obesity is closely associated with the development of cardiovascular (CV) disease, suggesting that it might be considered as an independent CV risk factor. However, the pathophysiological mechanisms responsible for the association between these 2 clinical entities remain largely unknown. Adipocytes are considered able to produce and secrete chemical mediators known as “adipokines” that may exert several biological actions, including those on heart and vessels. Of interest, a different adipokine profile can be observed in the plasma of patients with obesity or metabolic syndrome compared with healthy controls. We consider the main adipokines, focusing on their effects on the vascular wall and analyzing their role in CV pathophysiology.

Effects of different mesenchymal stromal cell sources and delivery routes in experimental emphysema

We sought to assess whether the effects of mesenchymal stromal cells (MSC) on lung inflammation and remodeling in experimental emphysema would differ according to MSC source and administration route. Emphysema was induced in C57BL/6 mice by intratracheal (IT) administration of porcine pancreatic elastase (0.1 UI) weekly for 1 month. After the last elastase instillation, saline or MSCs (1×105), isolated from either mouse bone marrow (BM), adipose tissue (AD) or lung tissue (L), were administered intravenously (IV) or IT. After 1 week, mice were euthanized. Regardless of administration route, MSCs from each source yielded: 1) decreased mean linear intercept, neutrophil infiltration, and cell apoptosis; 2) increased elastic fiber content; 3) reduced alveolar epithelial and endothelial cell damage; and 4) decreased keratinocyte-derived chemokine (KC, a mouse analog of interleukin-8) and transforming growth factor-β levels in lung tissue. In contrast with IV, IT MSC administration further reduced alveolar hyperinflation (BM-MSC) and collagen fiber content (BM-MSC and L-MSC). Intravenous administration of BM- and AD-MSCs reduced the number of M1 macrophages and pulmonary hypertension on echocardiography, while increasing vascular endothelial growth factor. Only BM-MSCs (IV > IT) increased the number of M2 macrophages. In conclusion, different MSC sources and administration routes variably reduced elastase-induced lung damage, but IV administration of BM-MSCs resulted in better cardiovascular function and change of the macrophage phenotype from M1 to M2.

Association between plasma apelin levels and coronary collateral development in patients with stable angina pectoris

Apelin is an endogenous ligand for the orphan G protein-coupled receptor (APJ receptor). Apelin is predominantly expressed in endocardial and vascular endothelial cells, while APJ receptor is localized to endothelial and smooth muscle cells, and cardiomyocytes. Apelin has recently attracted much attention due to its promotive effects on angiogenesis and its protective effects against mycardial infarction. In this issue of Atherosclerosis, Akboga et al. investigated plasma apelin levels in patients with stable angina and severe coronary artery stenosis and provided the first evidence that higher plasma apelin levels are associated with better coronary collateral development, suggesting that apelin plays a role in coronary collateral development.

High-dose atorvastatin reloading before percutaneous coronary intervention increased circulating endothelial progenitor cells and reduced inflammatory cytokine expression during the perioperative period

OBJECTIVE

We investigated atorvastatin reloading effects on endothelial progenitor cell (EPC) count and inflammatory cytokine expression after percutaneous coronary intervention (PCI) in patients with stable angina pectoris who had previously received long-term statin treatments.

METHODS

Patients with stable angina pectoris were treated with 80 mg atorvastatin 12 hours and 40 mg atorvastatin 2 hours before coronary angioplasty (n = 15) or preoperatively with 40 mg/d atorvastatin for 7 days (n = 15) or did not receive atorvastatin (n = 15). CD45-/133+/34+, CD45-/CD34+/kinase insert domain receptor (KDR)+, and CD45-/CD144+/KDR+ EPCs in the peripheral blood were determined by flow cytometry 1 hour before as well as 1 hour, 6 hours, and 24 hours after PCI. Soluble intercellular adhesion molecule 1 (sICAM-1), hypersensitive C-reactive protein (hCRP), and troponin-I (TnI) serum concentrations were analyzed immediately prior to and 24 hours after PCI.

RESULTS

In the 40mg Atorvastatin and control groups, none of the analyzed EPC blood concentrations changed significantly from 1h before operation to 1h and 6 h postoperative values. In contrast, the number of circulating early differentiation stage EPCs CD45-/133+/34+ and CD45-/CD34+/ KDR+ raised significantly from 1 h preoperative values (57.3±9.3; 57.3 ± 10.7) to 1 h postoperative ((74.4 ± 11.4; 78.8 ± 16.2), (p < 0.05)) and 6 h postoperative ((93 ± 16.9; 99.7 ± 11.9), (p < 0.05)) concentrations after coronary angioplasty in the 80mg Atorvastatin medication patients. In the control group, the sICAM-1 (174.55 ± 38.91 vs 204.11 ± 58.24) and hCRP (1.89 ± 1.93 vs 9.0 ± 11.1) serum concentrations at 24 hours after PCI were significantly elevated (P < .05) compared to preoperative values, whereas the increases in the 2 groups treated with atorvastatin were not significant. In addition, the rise in serum TnI concentration level from pre- to postoperative in the 80-mg (0.02 ± 0.02 vs 0.09 ± 0.08) and the 40-mg (0.01 ± 0.03 vs 1.2 ± 2.59) reloading groups was less than that of the controls (0.01 ± 0.02 vs 1.75 ± 3.09) (p < 0.05).

CONCLUSION

Our results suggested that high-dose atorvastatin application before PCI triggered early EPC circulation. Furthermore, postoperative inflammatory cytokine sICAM-1 as well as hCRP serum levels were reduced, while postinterventional myocardial injury marker TnI elevations were inversely correlated with statin reloadings.