Abstract
Purpose: :
Age-related macular degeneration (AMD) is a leading cause of central vision loss in the industrialized world. The etiology and pathogenic mechanisms contributing to the initiation and development of AMD are not well understood. The purpose of these experiments was to further elucidate molecular-genetic mechanisms of AMD in AMD cell and animal models.
Methods: :
Post-mortem human retinal RNA analysis; ARPE-19 cell culture; ApoE4+ transgenic mice; DNA array (Affymetrix, Santa Clara, CA); micro-RNA array (LC Sciences, Houston, TX); Northern analysis; RT-PCR; Western analysis; gel-shift analysis; miRBASE algorithms (Sanger Institute, Cambridge, UK); bioinformatics (Silicon Genetics, Redwood City, CA).
Results: :
Post-mortem AMD retina, cytokine- and peroxide-stressed ARPE-19 cells, and aged, apolipoprotein E4 positive (ApoE4+) transgenic mice exhibited up-regulation of beta-amyloid precursor protein (βAPP), cytoplasmic phospholipase A2 (cPLA2) and the inducible cyclooxygenase-2 (COX-2). Interestingly, the contiguous human cPLA2 and COX-2 genes (chr 1q25) are physically linked to the gene encoding the inflammatory regulator complement factor H (CFH) that, like the key modulator of βAPP trafficking, sortilin-1 (SORL1), was found to be down-regulated. Stress-mediated coordinate up-regulation of pathogenic gene signaling appears to involve a small family of stress-sensitive transcription factors (SSTFs) whose DNA binding sites are enriched in the immediate promoters of the βAPP, COX-2 and cPLA2 genes. These SSTFs include a DNA binding triad that includes the IL-1β-inducible hypoxia inducible factor-1 alpha (HIF-1α), the inflammation-regulatory transcription factor NF-ΚB, and the promoter specificity protein-1 (SP1). Another important regulatory target for increased NF-ΚB-DNA-binding is in the promoter of the precursor miRNA-146a gene, and the miRNA-146a target CFH mRNA was found to be significantly down-regulated. The mechanism for down-regulated SORL1 is currently under investigation.
Conclusions: :
As in neurodegenerative disease, the translation products of βAPP, cPLA2, COX-2, CFH or SORL1, or their catabolic metabolites or catalytic properties, propagate inflammatory and apoptotic signaling pathways that redirect retinal cellular fate towards apoptotic change. Up-regulated NF-ΚB and miR-146a appear to act in close concert to promote pathogenic gene expression, and integrated SSTF and micro-RNA-mRNA genetic regulatory circuits may contribute to retinal cell dysfunction and inflammatory aspects of AMD.
Keywords: retinal pigment epithelium • retinal degenerations: cell biology • genetics