Cacna2d1: a novel therapeutic target for lowering IOP

Abstract

Purpose : Glaucoma is a leading cause of blindness worldwide and intraocular pressure (IOP) is the only modifiable risk factor. Genetic variability is a major contributor to interpersonal differences in responses to IOP lowering therapies. Here, we have combined systems genetics analysis of aged BXD strains of mice with human GWAS and pharmacology to define and validate a novel genetic modifier of IOP.

Methods : We measured IOP in 66 BXD strains between 10–13 months-of-age using a TonoLab pen. Variation was mapped using GeneNetwork. Candidate genes were nominated based on expression patterns and known sequence variants segregating in the BXD family. The cellular localization of corresponding protein was evaluate by immunohistochemistry in mouse and human retina. The GLAUGEN/NEIGHBOR consortium database was used to identify SNPs within human candidate genes associated with POAG. IOP lowering effects of nimodipine and pregabalin were evaluated as eye drops in C57BL/6J (B6), BXD14 (B allele at major QTL) and BXD48 (D allele) strains (n = 6 for each strain). The minimum effective concentration was determined.

Results : Variation in IOP in the BXD family maps to Chr 5 with a LOD of 4.0 and a 1.5 LOD confidence interval from 14.2 to 18.8 Mb (Pclo to A921504A21Rik). The effect size is +1.0 mmHg/per B allele. Cacna2d1 is the best candidate and is cis-regulated in BXD retinal data sets. CACNA2D1 is expressed in ciliary body, trabecular meshwork, retina, and optic nerve in mouse and human. GLAUGEN/NEIGHBOR POAG meta-analyses revealed a SNP (rs4732474) nominally associated with POAG (P=0.0075), which is significant at the gene level. This candidate is a component of an L-type voltage gated calcium channel (CACN) regulating ionic transport. Nimodipine—an antagonist for the CACN pore—reduced IOP in B6 by 18.4±1.7%, BXD14 by 31.3±3.5% and BXD48 by 3.2±2.0% compared to baseline. Similarly, pregabalin, an antagonist for the α2δ1 subunit of CACN, reduced the IOP in B6 by 20.4±5.5%, BXD14 by 28.5±3.5% and BXD48 by 14.2±3.9%.

Conclusions : This is the first study to combine systems genetics, bidirectional studies using human GWAS, and pharmacology to identify and validate a genetic modulator of IOP. Both nimodipine and pregabalin lowered IOP significantly in strains with the B parent allele compared to strains with D parent allele. In the future, similar pharmaco-genetic studies could pave the way for improved POAG therapies tailored to individual genotypes.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.