Abstract
Purpose:
To identify genetic modifiers of intraocular pressure (IOP) using the enlarged BXD family of strains in combination with human GWAS glaucoma cohorts. The BXD family consists of inbred progeny strains of a cross between wildtype C57BL/6J and DBA/2J that harbors mutations in both Tyrp1 and Gpnmb and develops pigmentary dispersion glaucoma. We can exploit the known segregation of these mutations among progeny and eliminate from our analyses those that are mutant at both loci to remove any influence of pigmentary dispersion glaucoma on IOP.
Methods:
We acquired IOP estimates for parents and 68 progeny free of mutations in Tyrp1 and Gpnmb at 1-2, 3-5, 6-9, 10-13 and >13 months-of-age, using an induction impact tonometer. Conventional arrays and RNA-seq data were used to estimate gene expression from eyes of parents and progeny. IOP datasets were mapped using GeneNetwork (www.genenetwork.org). Candidate genes for high IOP/POAG are now being evaluated using combinations of the following criteria: (1) genes are located within confidence intervals of murine QTLs; (2) genes have coding differences segregating among progeny; (3) genes are expressed in the eye, and are associated with cis-expression QTL (eQTL); (4) expression of transcripts covaries with IOP; (5) genes have a plausible biological link to IOP and glaucoma; and most importantly, (6) genes are close to linkage peaks in the GLAUGEN and NEIGHBOR human GWAS studies of POAG and IOP.
Results:
We identify a robust eQTL in BXD mice strains aged 10-13 mo. Within this QTL, 21 candidates were nominated. The best SNP in each candidate for each subset (HTG, NTG and POAG overall) were identified using human data from the GLAUGEN/NEIGHBOR meta-analyses. The top five candidates were selected based on the Bonferroni-corrected p-value (0.0023). Top candidates were found to play critical roles in ionic transport regulation, nitric oxide synthesis and modulation, axon growth cone guidance regulation, and ciliary body function—all of which could be important for elevated IOP and possibly POAG.
Conclusions:
In this study using the expanded BXD family and human GWAS, we have identified five candidate genes that may modulate IOP. These new findings could pave the way for novel efficacious therapies for POAG using drug or gene delivery.
Keywords: 568 intraocular pressure •
536 gene modifiers •
535 gene microarray