Apelin-13: A Promising Biomarker for Age-Related Macular Degeneration?

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.

VEGFA Haplotype and VEGF-A and VEGF-R2 Protein Associations with Exudative Age-Related Macular Degeneration

Our study aimed to reveal the associations between VEGFA SNPs (rs1570360, rs699947, rs3025033, and rs2146323), their haplotypes, VEGF-A and VEGF-R2 serum concentrations, and early and exudative AMD. A total of 339 subjects with early AMD and 419 with exudative AMD groups, and 374 healthy subjects, were genotyped for four VEGFA SNPs (rs1570360, rs699947, rs3025033, and rs2146323). VEGF-A and VEGFR-2 serum concentrations were measured in exudative AMD and controls. The results revealed that rs3025033 G allele was significantly associated with lower odds of exudative AMD under the dominant model (OR = 0.67; 95% CI: 0.49–0.80; p = 0.0088) and additive (OR = 0.7; 95% CI: 0.54–0.90; p = 0.0058) models after Bonferroni correction. In the female group, rs3025033 AG genotype was associated with exudative AMD under the codominant model (OR = 0.57; 95% CI: 0.37–0.87; p = 0.009) and G allele under the dominant (OR = 0.55; 95% CI: 0.37–0.82; p = 0.0032) and additive models (OR = 0.60; 95% CI: 0.42–0.84; p = 0.0028). Haplotype analysis revealed that individuals carrying rs1570360, rs699947, rs3025033, and rs2146323 haplotype A-A-G-A had decreased risk of exudative AMD (OR = 0.46, 95% CI: 0.23–0.90; p = 0.023). The VEGF-A and VEGF-R2 serum concentrations did not differ between study groups; we found that patients with exudative AMD carrying at least one C allele at rs699947 have statistically significantly higher VEGF-A serum concentrations compared to AA genotype carriers (485.95 (945.93) vs. 194.97 (-), respectively, p = 0.046). In conclusion, we found that VEGFA rs3025033 and haplotype rs1570360A-rs699947A-rs3025033G- rs2146323A play a protective role for exudative AMD in the Caucasian population. Furthermore, rs699947 is associated with elevated VEGF-A serum concentrations in exudative AMD.

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.