In Vivo and In Vitro Studies Support That a New Splicing Isoform of OLR1 Gene Is Protective Against Acute Myocardial Infarction

Abstract

Abstract-Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), encoded by the OLR1 gene, is a scavenger receptor that plays a fundamental role in the pathogenesis of atherosclerosis. LOX-1 activation is associated with apoptosis of endothelial cells, smooth muscle cells (SMCs), and macrophages. This process is an important underlying mechanism that contributes to plaque instability and subsequent development of acute coronary syndromes. Independent association genetic studies have implicated OLR1 gene variants in myocardial infarction (MI) susceptibility. Because single nucleotide polymorphisms (SNPs) linked to MI are located in intronic sequences of the gene, it remains unclear as to how they determine their biological effects. Using quantitative real-time PCR and minigene approach, we show that intronic SNPs, linked to MI, regulate the expression of a new functional splicing isoform of the OLR1 gene, LOXIN, which lacks exon 5. Macrophages from subjects carrying the "non-risk" disease haplotype at OLR1 gene have an increased expression of LOXIN at mRNA and protein level, which results in a significant reduction of apoptosis in response to oxLDL. Expression of LOXIN in different cell types results in loss of surface staining, indicating that truncation of the C-terminal portion of the protein has a profound effect on its cellular trafficking. Furthermore, the proapoptotic effect of LOX-1 receptor in cell culture is specifically rescued by the coexpression of LOXIN in a dose-dependent manner. The demonstration that increasing levels of LOXIN protect cells from LOX-1 induced apoptosis sets a groundwork for developing therapeutic approaches for prevention of plaque instability.

Lectin‐like Oxidized Low‐density Lipoprotein Receptor‐1, a New Promising Target for the Therapy of Atherosclerosis?

“…Specific LOX-1 allelic polymorphisms confer protective effects by generating a new LOX-1 splice isoform lacking exon 5, called LOXIN. Macrophages carrying the "protective" LOX-1 haplotype display increased expression of LOXIN, which correlated with protection against ox-LDL-mediated apoptosis (Mango et al 2005). LOX-1 gene allelic variants (3 UTR/T) have been related to cardiovascular events and reduced antiplatelet activity induced by statins.…”

Reply to Novelli

“…2 In our publication, we did not find an association with acute myocardial infarction (AMI) in 677 subjects, but observed an association of the 501G4C polymorphism with CAD severity in a survey of 350 individuals.…”

OLR1 gene and coronary artery disease/acute myocardial infarction: replication in an independently collected sample

“…Both isoforms were detected in several cell types, such as endothelial cells, fibroblasts, and smooth muscle cells, and tissues, including the heart, kidney, and brain. 6 We were able to demonstrate that the OLR1/LOXIN mRNA ratio was 33% higher in human monocyte-derived macrophages of subjects homozygous for risk allele compared with homozygous for the nonrisk allele. 6 This suggests that the SNPs may result in reduced expression of LOXIN.…”

“…6 We were able to demonstrate that the OLR1/LOXIN mRNA ratio was 33% higher in human monocyte-derived macrophages of subjects homozygous for risk allele compared with homozygous for the nonrisk allele. 6 This suggests that the SNPs may result in reduced expression of LOXIN. Correspondingly, a relative increase in the amount of LOXIN was found in cells derived from subjects homozygous for the nonrisk allele, suggesting that the expression level of LOXIN influence the incidence of AMI in humans and, at least in part, explain the risk resulting from polymorphisms in the human OLR1 gene.…”

“…6 In fact, two different OLR1 transcripts were isolated in the mRNA extracted from human monocyte-derived macrophages. One of these products corresponded to the full-length transcript, whereas the other lacked exon 5, and we termed it LOXIN.…”