Pharmacogenomics of steroid-induced ocular hypertension: relationship to high-tension glaucomas and new pathophysiologic insight

Abstract

Adverse drug reactions are a frequent cause of worldwide morbidity and mortality. Glucocorticoids (GCs), commonly used to treat inflammatory diseases, alter gene expression with both beneficial and adverse consequences. When used in the eye, GCs cause steroid-induced ocular hypertension (SIOH) in 30-50% of patients, leading to steroid-induced glaucoma. Evidence suggests that predisposition to SIOH is genetically determined. Here we took a pharmacogenomic approach to discover DNA variants associated with SIOH. We identified 44 SNPs of genome-wide significance (p<5E-08) located at 26 risk loci out of a total of 531 SNPs of suggestive significance (p<5E-06) at 262 risk loci. Unlike SNPs identified in complex disease which are overwhelmingly common in frequency, most SNPs found here were rare or of low frequency, likely discoverable because of their large effect sizes. Follow-up analyses provide insight into the pathogenetic relationship of SIOH to high-tension glaucomas and suggest a new mechanistic paradigm for SIOH pathophysiology.

Keywords: GWAS; Pharmacogenomics; SNP; adverse drug reaction; gene expression; genomic variant; glaucoma; glucocorticoids; ocular hypertension; transcription.

Figure 1.. Manhattan plots for the Indianapolis-1 discovery GWASs.

The x axis is the position on each chromosome and the y axis is the −log10 P value from the GWAS for each SNP. The red dashed line demarcates the threshold for genome-wide significance [−log10(5E-08); p=5.0E-08]. The risk locus for each SNP of genome-wide significance is defined by the nearest genes to the SNP, as delineated on the plots. The quantitative trait (QT) used for each GWAS is indicated.

Figure 2.. GWAS prioritized target genes that cluster with the pathway “signaling by NOTCH”.

A schematic overview of the canonical Notch signaling pathway is shown, with white boxes indicating prioritized target genes of SNPs identified in this study. Notch receptors are synthesized as a single polypeptide that is O-fucosylated and glycosylated in the endoplasmic reticulum. POFUT1 encodes a Golgi-localized fucosyltransferase that performs the first step in glycosylation of the Notch EGF-like domains. Loss of POFUT1 severely inhibits Notch signaling^,. The Notch protein then moves to the trans-Golgi network, where it is cleaved by a Furin-like convertase(s) (S1), forming a heterodimer. CHAC1 encodes an inhibitor of this cleavage. The heterodimeric receptor is then transported to the cell membrane, where it binds with the ligand expressed in the neighboring cell. DLL4 and JAG2 encode members of the Notch ligand families Delta and Serrate, respectively. Receptor–ligand interaction initiates second cleavage (S2) within the extracellular domain. ADAM10 encodes one of only two proteinases known to effect this cleavage step (the other is ADAM17). After S2 cleavage, the Notch extracellular truncated fragment (NEXT), is ‘trans-endocytosed’ by the neighboring ligand-expressing cell, in a process that appears to be controlled by E3 ubiquitin ligases. This is followed by a 3^rd and 4^th cleavage (S3, S4) that occurs within the transmembrane domain and is mediated by a multi-protein γ-secretase. The intracellular domain of Notch (NICD) is then released and translocates into the nucleus and binds to the transcription factor CSL. This interaction leads to transcriptional activation by displacement of co-repressors (Co-R), including proteins encoded by TLE1, HDAC4, HDAC9, and TBLRX1. Simultaneous recruitment of co-activators (Co-A) occurs, such as members of the mastermind family, including the protein encoded by MAML3. Transcription factors encoded by TFDP2 and E2F3 bind to the promoter regions of Notch target genes, thereby enhancing their transcription. The protein encoded by WWC1 (also known as Kibra) is a notch target gene and a key component of Hippo/YAP signaling.