Investigating a downstream gene of Gpnmb using the systems genetics method.

Purpose:Glaucoma is characterized by optic nerve damage and retinal ganglion cell loss. The glycoprotein neuromedin B-associated (Gpnmb) gene is well-known to be involved in the glaucoma disease process. The purpose of this study is to identify a downstream gene through which Gpnmb affects the glaucoma phenotypes using a systems genetics approach. Methods:Retinal gene expression data for the BXD recombinant inbred (RI) strains (n=75) have previously been generated in our laboratory for a glaucoma study, and these data were used for genetic and bioinformatics analysis. Expression quantitative trait locus (eQTL) mapping and genetic correlation methods were used to identify a gene downstream of Gpnmb. Gene-set enrichment analysis was used to evaluate gene function and to construct coexpression networks. Results:The level of Gpnmb expression is associated with a highly statistically significant cis-eQTL. Stanniocalcin 1 (Stc1) has a significant trans-eQTL mapping to the Gpnmb locus. The expression of Gpnmb and Stc1 is highly correlated in the retina and other tissues, as well as with glaucoma-related phenotypes. Gene Ontology and pathway analysis showed that Stc1 and its covariates are highly associated with apoptosis, oxidative stress, and mitochondrial activity. A generated gene network indicated that Gpnmb and Stc1 are directly connected to and interact with other genes with similar biologic functions. Conclusions:These results suggest that Stc1 may be a downstream candidate of Gpnmb, and that both genes interact with other genes in a network to develop glaucoma pathogenesis through mechanisms such as apoptosis and oxidative stress.

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