The regulatory role of the apelin/APJ axis in scarring: Identification of upstream and downstream mechanisms.

Scarring, a prevalent issue in clinical settings, is characterized by the excessive generation of extracellular matrix within the skin tissue. Among the numerous regulatory factors implicated in fibrosis across various organs, the apelin/APJ axis has emerged as a potential regulator of fibrosis. Given the shared attribute of heightened extracellular matrix production between organ fibrosis and scarring, we hypothesize that the apelin/APJ axis also plays a regulatory role in scar development. In this study, we examined the expression of apelin and APJ in scar tissue, normal skin, and fibroblasts derived from these tissues. We investigated the impact of the hypoxic microenvironment in scars on apelin/APJ expression to identify the transcription factors influencing apelin/APJ expression. Through overexpressing or knocking down apelin/APJ expression, we observed their effects on fibroblast secretion of extracellular matrix proteins. We further validated these effects in animal experiments while exploring the underlying mechanisms. Our findings demonstrated that the apelin/APJ axis is expressed in fibroblasts from keloid, hypertrophic scar, and normal skin. The regulation of apelin/APJ expression by the hypoxic environment in scars plays a significant role in hypertrophic scar and keloid development. This regulation promotes extracellular matrix secretion through upregulation of TGF-ß1 expression via the PI3K/Akt/CREB1 pathway.

The apelin­apelin receptor signaling pathway in fibroblasts is involved in tumor growth via p53 expression of cancer cells.

Cancer­associated fibroblasts (CAFs) are pivotal in tumor progression. TP53­deficiency in cancer cells is associated with robust stromal activation. The apelin­apelin receptor (APJ) system has been implicated in suppressing fibroblast­to­myofibroblast transition in non­neoplastic organ fibrosis. The present study aimed to elucidate the oncogenic role of the apelin­APJ system in tumor fibroblasts. APJ expression and the effect of APJ suppression in fibroblasts were investigated for p53 status in cancer cells using human cell lines (TP53­wild colon cancer, HCT116, and Caco­2; TP53­mutant colon cancer, SW480, and DLD­1; and colon fibroblasts, CCD­18Co), resected human tissue samples of colorectal cancers, and immune­deficient nude mouse xenograft models. The role of exosomes collected by ultracentrifugation were also analyzed as mediators of p53 expression in cancer cells and APJ expression in fibroblasts. APJ expression in fibroblasts co­cultured with p53­suppressed colon cancer cells (HCT116sh p53 cells) was significantly lower than in control colon cancer cells (HCT116sh control cells). APJ­suppressed fibroblasts treated with an antagonist or small interfering RNA showed myofibroblast­like properties, including increased proliferation and migratory abilities, via accelerated phosphorylation of Sma­ and Mad­related protein 2/3 (Smad2/3). In addition, xenografts of HCT116 cells with APJ­suppressed fibroblasts showed accelerated tumor growth. By contrast, apelin suppressed the upregulation of phosphorylated Smad2/3 in fibroblasts. MicroRNA 5703 enriched in exosomes derived from HCT116sh p53 cells inhibited APJ expression, and inhibition of miR­5703 diminished APJ suppression in fibroblasts caused by cancer cells. APJ suppression from a specific microRNA in cancer cell­derived exosomes induced CAF­like properties in fibroblasts. Thus, the APJ system in fibroblasts in the tumor microenvironment may be a promising therapeutic target.

Therapeutic potential of apelin and Elabela in cardiovascular disease.

Apelin and Elabela (Ela) are peptides encoded by APLN and APELA, respectively, which act on their receptor APJ and play crucial roles in the body. Recent research has shown that they not only have important effects on the endocrine system, but also promote vascular development and maintain the homeostasis of myocardial cells. From a molecular biology perspective, we explored the roles of Ela and apelin in the cardiovascular system and summarized the mechanisms of apelin-APJ signaling in the progression of myocardial infarction, ischemia-reperfusion injury, atherosclerosis, pulmonary arterial hypertension, preeclampsia, and congenital heart disease. Evidences indicated that apelin and Ela play important roles in cardiovascular diseases, and there are many studies focused on developing apelin, Ela, and their analogues for clinical treatments. However, the literature on the therapeutic potential of apelin, Ela and their analogues and other APJ agonists in the cardiovascular system is still limited. This review summarized the regulatory pathways of apelin/ELA-APJ axis in cardiovascular function and cardiovascular-related diseases, and the therapeutic effects of their analogues in cardiovascular diseases were also included.

DNMT1 mediates proliferation, migration and invasion of extravillous trophoblasts by regulating the methylation level of APLNR.

INTRODUCTION: Proliferation, migration and invasion of extravillous trophoblasts (EVTs) play an important role in the progression of preeclampsia (PE). The purpose of this study was to investigate the molecular mechanism by which DNA methylase regulates the transcription level of APLNR and affects the phenotypic function of EVTs. MATERIALS AND METHODS: PE mice model and H/R model in HTR8/Svneo cells were constructed. Clinical samples of normal pregnant women and PE patients were collected. Expression and methylation level of APLNR in vivo and in vitro were detected. ChIP-qPCR was used to detect the binding of DNA methyltransferase at the APLNR promoter. The expression of DNA methyltransferase 1 (DNMT1), NO and eNOS in vitro were detected. EVTs proliferation, migration and invasion in vitro were detected. RESULTS: In placental tissues or HTR8/Svneo cells of the PE model group, the expression of APLNR was reduced and APLNR methylation level was up-regulated. There was no significant difference in the APLNR expression in placental tissues between normal pregnant women and PE patients. H/R conditions only promote the binding of DNMT1 at the APLNR promoter. DNMT1 interference decreased the enrichment degree of DNMT1 in APLNR promoter region and up-regulated the mRNA and protein levels of APLNR in vivo and in vitro. The activation of APLNR by Elabela (ELA) can promote eNOS transcription, thereby promoting cell proliferation and NO level, while eNOS inhibitor can reverse this effect. DNMT1 down-regulation inhibted APLNR methylation level, promoted eNOS transcription, and promoted EVTs proliferation, migration and invasion, which could be revised by the interference of APLNR. DISCUSSION: DNMT1 promotes eNOS transcription by inhibting APLNR methylation level, and promotes EVTs proliferation, migration and invasion, thus providing a new and broad application prospect for PE treatment.

Apelin receptor antagonist boosts dendritic cell vaccine efficacy in controlling angiogenic, metastatic and apoptotic-related factors in 4T1 breast tumor-bearing mice.

Apelin/APJ axis plays a critical role in cancer progression, thus its targeting inhibits tumor growth. However, blocking of Apelin/APJ axis in combination with immunotherapeutic approaches may be more effective. This study aimed to investigate the effects of APJ antagonist ML221 in combination with a DC vaccine on angiogenic, metastatic and apoptotic-related factors in a breast cancer (BC) model. Four groups of female BALB/c mice with 4T1-induced BC were treated with PBS, APJ antagonist ML221, DC vaccine, and "ML221 + DC vaccine". After completion of the treatment, the mice were sacrificed and the serum levels of IL-9 and IL-35 as well as the mRNA expression of angiogenesis (including VEGF, FGF-2, and TGF-ß), metastasis (including MMP-2, MMP-9, CXCR4) and apoptosis-related markers (Bcl-2, Bax, Caspase-3) in tumor tissues were determined using ELISA and real-time PCR, respectively. Angiogenesis was also evaluated by co-immunostaining of tumor tissues with CD31 and DAPI. Primary tumor metastasis to the liver was analyzed using hematoxylin-eosin staining. The efficiency of combination therapy with "ML221 + DC vaccine" was remarkably higher than single therapies in preventing liver metastasis compared to the control group. In comparison with the control group, combination therapy could significantly reduce the expression of MMP-2, MMP-9, CXCR4, VEGF, FGF-2, and TGF-ß in tumor tissues (P < 0.05). It also decreased the serum level of IL-9 and IL-35 compared with the control group (P < 0.0001). Moreover, vascular density and vessel diameter were significantly reduced in the combination therapy group compared with the control group (P < 0.0001). Overall, our findings demonstrate that combination therapy using a blocker of the apelin/APJ axis and DC vaccine can be considered a promising therapeutic program in cancers.

The apelin-apela receptor APJ is necessary for formation and healing of ischemia reperfusion-induced gastric ulcer in rats.

The apelinergic system widely expressed and regulates hormone-enzyme secretion, motility, and protective mechanisms of the stomach. This system consists of the apelin receptor (APJ) and two peptides known as apela and apelin. The IR-induced experimental gastric ulcer model is a well-known and commonly used one that induces hypoxia and causes the release of proinflammatory cytokines. Expressions of apelin and its receptor APJ are induced by hypoxia and inflammation in the gastrointestinal tract. Apelin has been shown to affect angiogenesis positively, considered the most critical component of the healing process. Although it is known that apelin and AJP expressions are induced by inflammatory stimuli and hypoxia, stimulate endothelial cell proliferation and have a role in regenerative angiogenesis, no information or has been found in the literature regarding the role of APJ in the formation and healing of gastric mucosal lesions induced by I/R. So, we conducted a study to clarify the role of APJ in formation and healing mechanisms of IR-induced gastric lesions. Male Wistar rats were divided into five groups; control, sham-operated, IR, APJ antagonist treated-IR group (F13A+IR), and the healing groups. F13A was intravenously given to the animals. Gastric lesion index, mucosal blood flow, PGE2, NOx, 4-HNE-MDA, HO activity, and protein expressions of VEGF and HO-1 were measured. F13A application before the IR increased the mucosal injury, F13A application following the ischemia delayed the mucosal healing during the reperfusion period. Consequently, blocking apelin receptors may worsen gastric injury due to the IR and delay mucosal healing.

Cancer apelin receptor suppresses vascular mimicry in malignant melanoma.

Several reports indicate that apelin is often over-expressed in tumors, and therefore it has been suggested that the apelin-apelin receptor (APJ) system may induce tumor progression. In contrast, our previous research revealed high expression of the apelin-APJ system in tumor blood vessels, suggesting its involvement in the regulation of tumor vessel formation and normalization, resulting in the suppression of tumor growth by promoting the infiltration of T cells. Thus, the effect of the apelin-APJ system on tumors remains controversial. In this report, to clarify the effect of apelin in tumor cells, we analyzed the function of APJ in tumor cells using APJ knock out (KO) mice. In APJ-KO mice, Apelin overexpression in B16/BL6 (B16) melanoma cells induced greater tumor growth than controls. In an APJ-KO melanoma inoculation model, although angiogenesis is suppressed compared to wild type, no difference is evident in tumor growth. We found that APJ deficiency promoted vascular mimicry in tumors. In vitro, cultured APJ-KO B16 cells demonstrated a spindle-like shape. This phenotypic change was thought to be induced by epithelial-mesenchymal transition (EMT) based on evidence that APJ-KO B16 cells show persistently high levels of the mesenchymal maker, Zeb1; however, we found that EMT did not correlate with the transforming growth factor-ß/smad signaling pathway in our model. We propose that apelin-APJ system in cancer cells induces tumor growth but negatively regulates EMT and tumor malignancy.

Reduced Apela/APJ system expression in patients with pulmonary artery hypertension secondary to chronic obstructive pulmonary disease.

BACKGROUND: Pulmonary artery hypertension (PAH) is a common disease that seriously threatens human physical and mental health. Chronic obstructive pulmonary disease (COPD) is the main cause of secondary PAH. OBJECTIVES: This study observed the differential expression of the endogenous Apela/APJ system in COPD patients with or without PAH. METHODS: A total of 69 COPD patients were enrolled, including 31 patients with PAH (COPD+PAH). Lung tissue from healthy controls, COPD patients, and COPD patients with PAH was used for RT-PCR and histological examination. RESULTS: The serum level of endogenous Apela in COPD+PAH patients was significantly lower than those in the control and COPD groups. Correlation analysis showed that systolic pulmonary artery pressure in COPD+PAH patients was negatively correlated with the serum level of endogenous Apela (r = -0.3842, p < 0.05). The percentage of intima thickening and muscularization of pulmonary arterioles was increased in COPD+PAH patients, while the expression of Apela/APJ was decreased. Compared with the healthy controls and COPD patients, the expression of endothelial markers vWF and CD34 mRNA in the pulmonary arterioles in COPD+PAH patients decreased, while the expression of interstitial markers α-SMA and vimentin mRNA was up-regulated. CONCLUSION: The present study suggests that expression of the Apela/APJ system is decreased in PAH secondary to COPD. The pathological changes involved in PAH secondary to COPD include thickening of the intima and muscularization of the pulmonary arterioles, as well as endothelial-to-mesenchymal transition. Corrective action targeting the diminished Apela/APJ system may be a promising therapeutic strategy for PAH in the future.

Expression and localization of apelin and apelin receptor (APJ) in buffalo ovarian follicles and corpus luteum and the in-vitro effect of apelin on steroidogenesis and survival of granulosa cells.

Apelin is an adipose tissue-derived hormone with many physiological functions, including the regulation of female reproduction. It acts through an orphan G protein-coupled receptor APJ/APLNR. The present study aimed to investigate the expression of apelin and its receptor APJ in the ovarian follicles and corpus luteum (CL) and the role of apelin on steroidogenesis and cell survival. Ovarian follicles were classified into four groups based on size and estradiol (E2) level in the follicular fluid as follows: (i) F1 (4-6 mm; <0.5 ng/mL) (ii) F2 (7-9 mm; 0.5-5 ng/mL) (iii) F3 (10-13 mm; 5-40 ng/mL) and (iv) F4 (dominant/pre-ovulatory follicle) (>13 mm; >180 ng/mL). The corpora lutea (CL) were categorized into early (CL1), mid (CL2), late luteal (CL3), and regressing (CL4) CL stages. Expression of apelin increased with follicle size, with significantly greatest in the dominant or pre-ovulatory follicle (P < 0.05). Expression of APJ was greater in large and dominant follicles than in small and medium follicles (P < 0.05). In CL, the mRNA and protein abundance of apelin and apelin receptor was greater during mid (CL2) and late luteal (CL3) stages as compared to early (CL1) and regressing (CL4) stages (P < 0.05). Both the factors were localized in granulosa and theca cells of follicles and small and large luteal cells of CL. The pattern of the intensity of immunofluorescence was similar to mRNA and protein expression. Granulosa cells were cultured in vitro and treated at 1, 10, and 10 ng/mL apelin-13 either alone or in the presence of the follicle-stimulating hormone (FSH) (30 ng/mL) or insulin-like growth factor-I (IGF-I) (10 ng/mL) for 48 h. The luteal cells were treated with apelin-13 at 1, 10, and 100 ng/mL doses for 48 h. Apelin treatment at 10 and 100 ng/ml significantly (P < 0.05) increased E2 secretion, cytochrome P450 aromatase or CYP19A1 expression in GC. In luteal cells, apelin at 10 ng/mL and 100 ng/mL significantly (P < 0.05) increased progesterone (P4) secretion and HSD3B1 expression. In GCs, apelin, either alone or in combination, increased PCNA expression and inhibited CASPASE3 expression suggesting its role in cell survival. In conclusion, this study provides novel evidence for the presence of apelin and receptor APJ in ovarian follicles and corpora lutea and the stimulatory effect on E2 and P4 production and promotes GC survival in buffalo, suggesting the role of apelin in follicular and luteal functions in buffalo.

Variations in protein levels of the apelinergic system in adipose tissue of hypertensive individuals with class 3 obesity.

The aim of this study was to investigate the expression of apelin (APLN) and its receptor (APLNR) in visceral adipose tissue (VAT), and its effect on the downstream expression of endothelial nitric oxide synthase (eNOS) in individuals with class 3 obesity, with or without hypertension. Seventy-five unrelated individuals presenting obesity class 3 with or without hypertension were included. Gene expression of APLN, and APLNR were analyzed in VAT, by reverse transcription quantitative polymerase chain reaction. The APLN, APLNR and eNOS (total and phosphorylated) levels in VAT were evaluated by Western blot. Analysis of differences between groups of APLN, APLNR and eNOS were performed by a logistic regression adjusting by confounding factors. Forty-five individuals with hypertension formed the case group, and 30 individuals constituted the control group. The APLN mRNA and protein levels were higher in the group of individuals with hypertension versus individuals without hypertension (p = 0.027 and p = 0.036, respectively). Meanwhile, APLNR mRNA and protein levels in subjects with hypertension were lower versus the group of subjects without hypertension (p = 0.001 and p = 0.008, respectively). Further, the group with hypertension presented a lower level of phosphorylation of eNOS Ser1177, compared to the control group (p = 0.002). In conclusion, individuals with class 3 obesity and hypertension present a modified APLN/APLNR expression in visceral adipose tissue, which could be secondary to reduced eNOS phosphorylation.

Presence and localization of apelin and its cognate receptor in canine testes using immunohistochemical and RT-PCR techniques.

Apelin, a member of the adipokine family, is a novel endogenous peptide which regulates the male reproductive system of mammals by interacting with a specific receptor. Recent studies have highlighted that apelin may play a role in the regulation of reproduction by reducing testosterone production and inhibiting LH secretion. To the best of our knowledge, there is no available data on the presence of the apelin and its receptor in canine testes. Therefore, the aim of this study was to reveal the presence of apelin and evaluate its distribution in the canine testes using immunohistochemical and RT-PCR techniques. For this purpose, five fertile and healthy male dogs were subjected to elective orchiectomy. The immunohistochemical reaction revealed the presence of apelin and its receptor in the canine testes. Apelin was localized in spermatids and spermatozoa with a positive signal in the "acrosomal bodies". As regards the apelin receptor, a positive immunoreaction was detected in the cytoplasm of the cells localized near to the basal membrane of the seminiferous tubules and in the cytoplasm of Leydig cells. The RT-PCR analysis showed the presence of transcripts for apelin and apelin receptor in all of the samples under study. A 35kDa band confirmed apelin receptor protein expression in all of the samples analysed. In conclusion, the paracrine and endocrine role of apelin and its cognate receptor on male reproduction reported in humans and laboratory animals could also be hypothesized in dogs.

Inducible apelin receptor knockdown reduces differentiation efficiency and contractility of hESC-derived cardiomyocytes.

AIMS: The apelin receptor, a G protein-coupled receptor, has emerged as a key regulator of cardiovascular development, physiology, and disease. However, there is a lack of suitable human in vitro models to investigate the apelinergic system in cardiovascular cell types. For the first time we have used human embryonic stem cell-derived cardiomyocytes (hESC-CMs) and a novel inducible knockdown system to examine the role of the apelin receptor in both cardiomyocyte development and to determine the consequences of loss of apelin receptor function as a model of disease. METHODS AND RESULTS: Expression of the apelin receptor and its ligands in hESCs and hESC-CMs was determined. hESCs carrying a tetracycline-inducible short hairpin RNA targeting the apelin receptor were generated using the sOPTiKD system. Phenotypic assays characterized the consequences of either apelin receptor knockdown before hESC-CM differentiation (early knockdown) or in 3D engineered heart tissues as a disease model (late knockdown). hESC-CMs expressed the apelin signalling system at a similar level to the adult heart. Early apelin receptor knockdown decreased cardiomyocyte differentiation efficiency and prolonged voltage sensing, associated with asynchronous contraction. Late apelin receptor knockdown had detrimental consequences on 3D engineered heart tissue contractile properties, decreasing contractility and increasing stiffness. CONCLUSIONS: We have successfully knocked down the apelin receptor, using an inducible system, to demonstrate a key role in hESC-CM differentiation. Knockdown in 3D engineered heart tissues recapitulated the phenotype of apelin receptor down-regulation in a failing heart, providing a potential platform for modelling heart failure and testing novel therapeutic strategies.

The G protein-coupled receptor ligand apelin-13 ameliorates skeletal muscle atrophy induced by chronic kidney disease.

BACKGROUND: Targeting of the apelin-apelin receptor (Apj) system may serve as a useful therapeutic intervention for the management of chronic kidney disease (CKD)-induced skeletal muscle atrophy. We investigated the roles and efficacy of the apelin-Apj system in CKD-induced skeletal muscle atrophy. METHODS: The 5/6-nephrectomized mice were used as CKD models. AST-120, a charcoal adsorbent of uraemic toxins (8 w/w% in diet), or apelin (1 µmol/kg) was administered to CKD mice to investigate the mechanism and therapeutic potential of apelin on CKD-induced skeletal muscle atrophy. The effect of indoxyl sulfate, a uraemic toxin, or apelin on skeletal muscle atrophy was evaluated using mouse myoblast cells (C2C12 cells) in vitro. RESULTS: Skeletal muscle atrophy developed over time following nephrectomy at 12 weeks, as confirmed by a significant increase of atrogin-1 and myostatin mRNA expression in the gastrocnemius (GA) muscle and a decrease of lower limb skeletal muscle weight (P < 0.05, 0.01 and 0.05, respectively). Apelin expression in GA muscle was significantly decreased (P < 0.05) and elabela, another Apj endogenous ligand, tended to show a non-significant decrease at 12 weeks after nephrectomy. Administration of AST-120 inhibited the decline of muscle weight and increase of atrogin-1 and myostatin expression. Apelin and elabela expression was slightly improved by AST-120 administration but Apj expression was not, suggesting the involvement of uraemic toxins in endogenous Apj ligand expression. The administration of apelin at 1.0 µmol/kg for 4 weeks to CKD mice suppressed the increase of atrogin-1 and myostatin, increased apelin and Apj mRNA expression at 30 min after apelin administration and significantly ameliorated weight loss and a decrease of the cross-sectional area of hindlimb skeletal muscle. CONCLUSIONS: This study demonstrated for the first time the association of the Apj endogenous ligand-uraemic toxin axis with skeletal muscle atrophy in CKD and the utility of therapeutic targeting of the apelin-Apj system.

The investigation of apelin and apelin receptor expressions in mouse endometrium during peri-implantation period.

BACKGROUND: Fertilization, pre-implantation embryo development, implantation, and decidualization are critical for a healthy pregnancy. Successful implantation requires a competent blastocyst and a receptive uterus. Apelin was purified from the bovine stomach in 1998. Apelin receptor (APJ) is a member of G protein-coupled receptors. Apelin/APJ system's physiological role was shown in cardiovascular system, immune response, stress response, fluid regulation, nutrient uptake, angiogenesis, and adipoinsular axis; however, whether apelin/APJ system plays a role in implantation is unknown. In our study, we aimed to evaluate the localization and expressions of the apelin/APJ system in the peri-implantation period mouse uterus. METHODS: Uteri and implantation sites were collected from mice on the estrous phase and the 1st, 4th, 5th, 6th, and 8th days of pregnancy. Also, inter-implantation sites were collected from the 5th day of the pregnancy group. Localization and expressions of apelin and APJ were determined by immunohistochemistry and Western blot, respectively. RESULTS: Apelin and APJ were expressed in the luminal and gland epithelium, the stroma of all experimental groups. Two isoforms of apelin-8 and 16 kDa were detected by Western blot. While apelin expression increased from the estrous to the 8th day of pregnancy, APJ expression increased from the estrous to the 4th day of pregnancy, reached the highest expression level, then decreased. CONCLUSIONS: Our findings suggest that the apelin/APJ system might be involved in implantation and decidualization. Our findings will guide further studies and may help elucidate the underlying causes of implantation failure and pregnancy loss.

Targeting APLN/APJ restores blood-testis barrier and improves spermatogenesis in murine and human diabetic models.

Type 2 diabetes mellitus is one of the most prevalent metabolic diseases presenting with systemic pathologies, including reproductive disorders in male diabetic patients. However, the molecular mechanisms that contributing to spermatogenesis dysfunction in diabetic patients have not yet been fully elucidated. Here, we perform STRT-seq to examine the transcriptome of diabetic patients' testes at single-cell resolution including all major cell types of the testis. Intriguingly, whereas spermatogenesis appears largely preserved, the gene expression profiles of Sertoli cells and the blood-testis barrier (BTB) structure are dramatically impaired. Among these deregulate pathways, the Apelin (APLN) peptide/Apelin-receptor (APJ) axis is hyper-activated in diabetic patients' testes. Mechanistically, APLN is produced locally by Sertoli cells upon high glucose treatment, which subsequently suppress the production of carnitine and repress the expression of cell adhesion genes in Sertoli cells. Together, these effects culminate in BTB structural dysfunction. Finally, using the small molecule APLN receptor antagonist, ML221, we show that blocking APLN/APJ significantly ameliorate the BTB damage and, importantly, improve functional spermatogenesis in diabetic db/db mice. We also translate and validate these findings in cultured human testes. Our findings identify the APLN/APJ axis as a promising therapeutic target to improve reproduction capacity in male diabetic patients.

High APLN Expression Predicts Poor Prognosis for Glioma Patients.

Apelin (APLN) is an endogenous ligand of the G protein-coupled receptor APJ (APLNR). APLN/APLNR system was involved in a variety of pathological and physiological functions, such as tumorigenesis and development. However, its prognostic roles in patients with central nervous system (CNS) cancers remain unknown. The present study was designed to explore the expression profile, prognostic significance, and interaction network of APLN/APLNR by integrating data from Oncomine, GEPIA, LOGpc, STRING, GeneMANIA, and immunohistochemical staining. The results demonstrated that APLN and APLNR mRNA expression were significantly increased in CNS cancers, including both low-grade glioma (LGG) and glioblastoma (GBM), when compared with normal CNS tissues. The high APLN, but not APLNR, expression was significantly correlated with overall survival (OS), recurrence free survival (RFS), and progression free survival (PFS) of LGG patients. However, neither APLN nor APLNR expression was significantly related to prognostic value in terms of OS, disease free interval (DFI), disease specific survival (DSS), or progression free interval (PFI) for GBM patients. Additionally, immunohistochemistry staining confirmed the increased APLN expression in tissues of LGG patients with grade II than grade I. These results showed that an elevated APLN level could predict poor OS, RFS, and PFS for LGG patients, and it could be a promising prognostic biomarker for LGG.

The Apelin/APLNR system modulates tumor immune response by reshaping the tumor microenvironment.

Apelin is an endogenous ligand of the Apelin receptor (APLNR), a seven-transmembrane G protein-coupled receptor, which is widely distributed in human tissue. The Apelin/APLNR system is involved in regulating several physiological and pathological processes. The Apelin expression is increased in a variety of cancer and the Apelin/APLNR system could regulate the development of tumors through mediating autophagy, apoptosis, pyroptosis, and other biological processes to regulate tumor cell proliferation, migration, and invasion. The Apelin/APLNR system also participates in immune response and immune regulation through PI3K-Akt, ERK-MAPK, and other signal pathways. The latest research points out that there is a negative regulatory relationship between APLNR and immune checkpoint PD-L1. In this review, we outline the significance of the Apelin/APLNR signaling pathway in tumorigenesis and its immune regulation. These endeavors provide new insights into the translational application of Apelin/APLNR in cancer and may contribute to the promotion of more effective treatments for cancers.

Multiple roles of apelin/APJ system in eye diseases.

Apelin is an endogenous ligand of G protein-coupled receptor (APJ), and they compose apelin/APJ system. Apelin/APJ system is widely distributed in tissues and plays pleiotropic roles. Attractively, more emphasis has recently been placed on the effects of apelin/APJ system in eye diseases, such as retinopathy of prematurity (ROP), diabetic retinopathy (DR) and diabetic macular edema (DME). In this review, we elaborated the roles of apelin/APJ system in the pathophysiological processes of eye. Concretely, apelin/APJ system induces retinal gliosis and angiogenesis. Hypoxia-inducible factors (HIFs) are involved in apelin/APJ system-triggered ROP progress. Apelin/APJ system mediates DR-induced retinopathy. Apelin/APJ system maintains retinal functions and health by protecting Müller cells from apoptosis. Apelin/APJ system suppresses the NMDA-induced retinal ganglion cell (RGC) loss to protect optic nerve damage. Overall, apelin/APJ system is a potential therapeutic target for eye disease.

APLNR Regulates IFN-γ signaling via ß-arrestin 1 mediated JAK-STAT1 pathway in melanoma cells.

The apelin receptor (APLNR) regulates many biological processes including metabolism, angiogenesis, circulating blood volume and cardiovascular function. Additionally, APLNR is overexpressed in various types of cancer and influences cancer progression. APLNR is reported to regulate tumor recognition during immune surveillance by modulating the IFN-γ response. However, the mechanism of APLNR cross-talk with intratumoral IFN-γ signaling remains unknown. Here, we show that activation of APLNR up-regulates IFN-γ signaling in melanoma cells through APLNR mediated ß-arrestin 1 but not ß-arrestin 2 recruitment. Our data suggests that ß-arrestin 1 directly interacts with STAT1 to inhibit STAT1 phosphorylation to attenuate IFN-γ signaling. The APLNR mutant receptor, I109A, which is deficient in ß-arrestins recruitment, is unable to enhance intratumoral IFN-γ signaling. While APLNR N112G, a constitutively active mutant receptor, increases intratumoral sensitivity to IFN-γ signaling by enhancing STAT1 phosphorylation upon IFN-γ exposure. We also demonstrate in a co-culture system that APLNR regulates tumor survival rate. Taken together, our findings reveal that APLNR modulates IFN-γ signaling in melanoma cells and suggest that APLNR may be a potential target to enhance the efficacy of immunotherapy.

Evaluation of angiogenic apelin/apelin receptor axis in normal prostate, high grade prostatic intraepithelial neoplasia and prostatic adenocarcinoma.

INTRODUCTION AND OBJECTIVES: Prostate cancer is one of the most commonly diagnosed cancers in American men. Apelin is an endogenous peptide identified as the ligand of the G protein-associated apelin receptor. Apelin and apelin receptor have many tissues distribution and they participate in pathological processes, such as cancer. Apelin stimulates cancer angiogenesis. However, there are insufficient data in the literature regarding the role of apelin/apelin receptor in normal tissue, highgrade prostatic intraepithelial neoplasia, and prostatic adenocarcinoma tissues. Therefore, this study aimed to investigate the apelin and apelin receptor expression levels in tissues of normal prostate tissue, high-grade prostatic intraepithelial neoplasia, and prostatic adenocarcinoma. MATERIALS AND METHODS: In this study, 38 samples of patients undergoing radical prostatectomy were used. Among 38 samples; 20 patients were with prostatic adenocarcinoma, 18 patients were with high-grade prostatic intraepithelial neoplasia and adjacent normal prostatic tissue areas. The immunolocalisation of apelin and apelin receptor in these tissues were determined immunohistochemically. RESULTS: Apelin and apelin receptor expressions were higher in prostatic adenocarcinoma than normal prostate tissue and high-grade prostatic intraepithelial neoplasia. Apelin receptor expression was also increased in high-grade prostatic intraepithelial neoplasia compared to normal tissue. CONCLUSION: Apelin and apelin receptor are increase in the process of prostate carcinogenesis. This increase may adversely affect the clinical course of prostate cancer patients by stimulating angiogenesis, which is important for invasion and metastasis in prostate cancer.