Researchers at the Sagol School of Neuroscience at Tel Aviv University might have made a breakthrough discovery in the treatment of age-related macular degeneration (AMD) by identifying two vital proteins in the development and operation of retinal pigment epithelium (RPE) cells.
Give me some background.
RPE cells are vital for the health, survival, and function of the retinal photoreceptors and the choroid. In AMD, RPE dysfunction causes progressive accumulation of inflammatory deposits (drusen) within Bruch’s membrane that is excreted by the RPE, which can lead to hypoxia, choroidal neovascularization, and/or progressive loss of RPE and photoreceptor cells.
AMD has a known significant genetic component. While genome-wide association studies (GWASs) on AMD have identified around 50 loci that have a substantial association with an increased risk for the disease—many were found in noncoding regions between genes.
The functions and modes of operation of these loci are still largely unknown.
Talk about the study.
Researchers identified the regulatory regions that control the differentiation and maintenance of the genes involved in AMD pathophysiology. They knocked down different proteins using in-vivo functional mouse models, RPE generated from human embryonic stem cells (hES-RPE), and global transcriptomic and proteomic analyses.
What did they find?
LHX2 and OTX2 were identified as key tissue-specific transcription factors (TF) that bind to specific regulatory sites in the genome to determine which genes will be expressed in RPE cells.
Chromatin immunoprecipitation followed by sequencing (ChIP-seq) was performed to detect the binding sites where the proteins attach to the DNA.
Paired with RNA sequencing of the hES-RPE, the researchers discovered that the binding sites of the two proteins were close to each other, suggesting that they cooperate upstream to ensure the activation of tissue-specific target genes.
They also found that these sites were previously identified as key players in molecular pathways underlying AMD pathogenesis.
Connecting the dots.
Altering the expression of the transient receptor potential melastatin 1 (TRPM1) gene in the RPE made it more difficult for the transcriptional proteins LHX2 and OTX2 to find and bind with their binding sites.
This caused a reduction in the expression of a nearby gene regulated by these proteins, which encodes the TRPM ion channel. Subsequently, this decrease in the gene’s activity affected the entire tissue, increasing the risk of developing AMD.
Significance?
Ruth Ashery-Padan, PhD, co-author of the study, explained, “We believe that our novel research methodology will enable the identification and mapping of many other genetic mechanisms related to AMD and other complex genetic diseases.”